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Giardiasis Surveillance — United States, 2011–2012

Julia E. Painter, PhD

Julia W. Gargano, PhD

Sarah A. Collier, MPH

Jonathan S. Yoder, MPH

Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC


Corresponding author: Julia W. Gargano, PhD, National Center for Emerging and Zoonotic Infectious Diseases, CDC. Telephone: 404-718-4893; E-mail: igc5@cdc.gov.


Abstract

Problem/Condition: Giardiasis is a nationally notifiable gastrointestinal illness caused by the protozoan parasite Giardia intestinalis.

Reporting Period: 2011–2012.

Description of System: Forty-four states, the District of Columbia, New York City, the Commonwealth of Puerto Rico, and Guam voluntarily reported cases of giardiasis to CDC through the National Notifiable Diseases Surveillance System (NNDSS).

Results: For 2011, a total of 16,868 giardiasis cases (98.8% confirmed and 1.2% nonconfirmed) were reported; for 2012, a total of 15,223 cases (98.8% confirmed and 1.3% nonconfirmed) were reported. In 2011 and 2012, 1.5% and 1.3% of cases, respectively, were associated with a detected outbreak. The incidence rates of all reported cases were 6.4 per 100,000 population in 2011 and 5.8 per 100,000 population in 2012. This represents a slight decline from the relatively steady rates observed during 2005–2010 (range: 7.1–7.9 cases per 100,000 population). In both 2011 and 2012, cases were most frequently reported in children aged 1–4 years, followed by those aged 5–9 years and adults aged 45–49 years. Incidence of giardiasis was highest in Northwest states. Peak onset of illness occurred annually during early summer through early fall.

Interpretation: For the first time since 2002, giardiasis rates appear to be decreasing. Possible reasons for the decrease in rates during 2011–2012 could include changes in transmission patterns, a recent change in surveillance case definition, increased uptake of strategies to reduce waterborne transmission, or a combination of these factors. Transmission of giardiasis occurs throughout the United States, with more frequent diagnosis or reporting occurring in northern states. Geographical differences might suggest actual regional differences in giardiasis transmission or variation in surveillance capacity across states. Six states did not report giardiasis cases in 2011–2012, representing the largest number of nonreporting states since giardiasis became nationally notifiable in 2002. Giardiasis is reported more frequently in young children, which might reflect increased contact with contaminated water or ill persons, or a lack of immunity.

Public Health Action: Educational efforts to decrease exposure to unsafe drinking and recreational water and prevent person-to-person transmission have the potential to reduce giardiasis transmission. The continual decrease in jurisdictions opting to report giardiasis cases could negatively impact the ability to interpret national surveillance data; thus, further investigation is needed to identify barriers to and facilitators of giardiasis case reporting. Existing state and local public health infrastructure supported through CDC (e.g., Epidemiology and Laboratory Capacity grants and CDC-sponsored Council of State and Territorial Epidemiologists Applied Epidemiology Fellows) could provide resources to enhance understanding of giardiasis epidemiology.

Introduction

Giardia intestinalis (also known as G. lamblia and G. duodenalis), a flagellated protozoan, is the most common intestinal parasite of humans identified in the United States (1), and a common cause of outbreaks associated with untreated surface and groundwater (2,3). Annually, an estimated 1.2 million cases occur in the United States (4); and hospitalizations resulting from giardiasis cost approximately $34 million (5).

Giardiasis is generally a self-limited illness typically characterized by diarrhea, abdominal cramps, bloating, weight loss, and malabsorption; asymptomatic infection also occurs frequently (6–8). Case reports and epidemiologic studies have associated giardiasis with the development of chronic enteric disorders, allergies, chronic fatigue, and reactive arthritis (9–14).

Giardia infection is transmitted by the fecal-oral route and results from the ingestion of Giardia cysts through the consumption of fecally contaminated food or water or through person-to-person (or, to a lesser extent, animal-to-person) transmission (15). The cysts are environmentally hardy, moderately chlorine tolerant, and infectious immediately upon being excreted in feces (16). The infectious dose is low; ingestion of 10 cysts has been reported to cause infection (16). Infected persons have been reported to shed 108–109 cysts in their stool per day and to excrete cysts for months (16–18). Effective therapies are available for patients with symptomatic giardiasis, including metronidazole, tinidazole, nitazoxanide, paromomycin, furazolidone, albendazole, and quinacrine (19).

Giardia is primarily transmitted through ingestion of infected human waste (20,21). Drinking untreated water from lakes and rivers, swimming, having contact with some animal species, and sexual practices involving fecal contact might increase risk for giardiasis (22). Giardiasis is often detected in international travelers (23,24) and among internationally adopted children (25). Transmission to close contacts of infected persons can also occur, including to children in child-care settings and their caregivers (18,26) or persons with occupational exposure to human waste (20, 21).

CDC recommends that health-care providers consider giardiasis in their differential diagnosis when a patient experiences diarrhea lasting >3 days. Routine examination of stool for ova and parasites does not always include testing for Giardia (27); thus, health-care providers should specifically request Giardia testing. Cyst excretion can be intermittent. Because the parasite might not be detected in a given stool specimen, three stool specimens collected on separate days should be examined before considering test results to be negative (28). Direct fluorescent antibody (DFA) testing is an extremely diagnostically sensitive and specific detection method and is considered the standard in Giardia testing (29).

In the United States, Giardia has been reported since 1992 and became a nationally notifiable disease in 2002. Surveillance data for 1992–2010 have been published previously (3034). This report summarizes national giardiasis surveillance data for 2011–2012. Federal, state, and local public health agencies can use these giardiasis surveillance data to better understand the epidemiology of giardiasis in the United States, design efforts to prevent the spread of disease, and establish research priorities.

Methods

Case Definition

The first national case definition was published in 1997 (35), and a revised case definition was published in 2011 (36). The current (2011) case definition differs from the 1997 definition in clarifying that clinical symptoms are necessary for categorizing giardiasis cases as confirmed.

Giardiasis is an illness caused by the protozoan Giardia intestinalis (also known as G. lamblia or G. duodenalis) and characterized by gastrointestinal symptoms (e.g., diarrhea, abdominal cramps, bloating, weight loss, or malabsorption). A confirmed case of giardiasis is defined as a case that meets the clinical description and the criteria for laboratory confirmation. Laboratory-confirmed giardiasis is defined as the detection of Giardia organisms, antigen, or DNA in stool, intestinal fluid, tissue samples, biopsy specimens, or other biological samples (36).

Nonconfirmed cases of giardiasis include probable, suspected, and unknown cases. A probable case of giardiasis meets the clinical description and is epidemiologically linked to a confirmed case (36). A national case definition for suspected cases of giardiasis does not exist; the definition varies by state. If cases are not classified as confirmed, probable, or suspected, then they are considered unknown.

Reporting

Forty-four states, the District of Columbia (DC), New York City (NYC), the Commonwealth of Puerto Rico, and Guam voluntarily reported cases of giardiasis to CDC through the National Notifiable Diseases Surveillance System (NNDSS) in 2011 and 2012. Giardiasis was not reportable in Kentucky, Mississippi, North Carolina, Oklahoma, Tennessee, and Texas. Reports include the patient's place of residence (state), age, sex, race, ethnicity (Hispanic or non-Hispanic), date of symptom onset, and whether the case is outbreak-associated. As has been done historically, the criteria for CDC's annual summary of notifiable diseases were used to classify case status (37). Because data in this report were finalized at a different time, the number of cases differs slightly from the number reported in CDC's annual summary of notifiable diseases.

Analysis

National giardiasis surveillance data for 2011–2012 were analyzed using statistical software. Numbers, percentages, and incidence rates (cases per 100,000 population) of giardiasis were calculated in aggregate and separately for the United States and territories. Rates were calculated by dividing the number of reported new giardiasis cases by each year's mid-year census estimates for the reporting jurisdictions and multiplying by 100,000 (38). In addition to analyzing data nationally and by reporting jurisdiction, data were analyzed by region (Northeast, Midwest, South, and West regions), as defined by the U.S. Census Bureau (39). To account for differences in the seasonal use of recreational water, the West region was further subdivided into Northwest and Southwest. To examine reporting over time, giardiasis rates per 100,000 population were calculated by year (from 1993 to 2012) and case type (confirmed or nonconfirmed). To assess current patterns in reporting, average annual giardiasis rates per 100,000 population were calculated by demographic variables (e.g., age and sex) and by month of symptom onset across 2011–2012 combined. This was performed by summing all cases occurring in the 2-year period, and then dividing by the sum of the number of persons in reporting jurisdictions in each year, and multiplying by 100,000. Rates could not be calculated for some variables (race and ethnicity) because of a large percentage of reports missing data (>20%) for these variables.

Results

During 2011–2012, all jurisdictions in the United States where giardiasis is reportable (including 44 states, DC, and NYC) voluntarily reported giardiasis cases to CDC through the National Notifiable Diseases Surveillance System (NNDSS). Among United States territories, Puerto Rico reported cases in 2011–2012, and Guam reported cases in 2012. A total of 16,868 giardiasis cases were reported in 2011 (98.8% confirmed), and 15,223 cases were reported in 2012 (98.8% confirmed) (Table 1). The rates of reported cases were 6.4 per 100,000 population in 2011 and 5.8 in 2012. This represents a slight decline from the relatively steady rates observed during 2005–2010 (range: 7.1–7.9 cases per 100,000 population), and a further decline from the peak of 13.84 cases per 100,000 population reported in 1995 (Figure 1). Approximately 99% of cases were confirmed for both 2011 and 2012, which is consistent with previous years. Of all cases reported for 2011 and 2012, 1.5% (251 of 16,868) and 1.3% (200 of 15,223) were reported to be associated with a detected outbreak (Table 1).

By region, the rates of reported giardiasis cases per 100,000 population ranged from 4.8 in the Southwest to 9.4 in the Northwest in 2011 and 4.6 in the Southwest and South to 8.5 in the Northwest in 2012 (Table 1). By state, giardiasis rates were lowest in Arizona (2.1 in 2011 and 1.7 in 2012) and highest in Vermont (35.6 in 2011 and 29.2 in 2012); 10 jurisdictions had rates higher than 10 per 100,000 population in 2012 (Figure 2, Table 1). The categories delineated in Figure 2 were initially used in the 1998–2002 giardiasis surveillance summary (31). In this and previous surveillance summaries they have remained the same to allow for comparison over time.

Surveillance data displayed a bimodal age distribution, with the largest number and rate of reported cases occurring among young children aged 1–9 years, with a smaller, flatter peak among middle-aged adults aged 40–49 years (Figure 3). In both 2011 and 2012, the largest number of cases was reported in children aged 1–4 years followed by those aged 5–9 years and adults aged 45–49 years. During 2011–2012, the rate of reported giardiasis per 100,000 population was highest in children aged 1–4 years (16.4) and 5–9 years (8.4) followed by adults aged 40–44 years (6.3) and 45–49 years (6.2). Rates were lowest among adults aged ≥80 years (2.7 per 100,000 population).

During 2011–2012, a total of 18,437 (57.7%) patients were male and 13,354 (41.8%) were female; 190 (0.6%) were missing data on sex (Table 2). The majority of cases for which data on race were available occurred among whites, followed by blacks, and Asians/Pacific Islanders (Table 2). However, data on race were not included for 41.2% of total annual case reports. Although 6.5% (2,074 of 16,590) of patients were identified as Hispanic, data on ethnicity were lacking for 48.1% of total annual case reports.

Analysis of rates by age and sex showed that giardiasis rates were higher among males in almost every age group (Figure 4). This difference was most pronounced among males aged 45–49 years. However, in persons aged 65–69 years, rates were slightly higher among females than males (5.1 versus 4.9 per 100,000 population).

Date of symptom onset was reported for 17,105 (53.5%) of the 31,981 cases during 2011–2012. The number of cases by symptom onset peaked in late July to early August (n = 1,075), which was 2.2 times higher than the lowest number of cases by symptom onset in February (n = 480) (Figure 5).

Discussion

National giardiasis surveillance data are critical in assessing the disease prevalence and epidemiologic characteristics of giardiasis in the United States. Following a gradual decline in case reports during 1996–2001, the number of case reports and disease rates stabilized during 2002–2010, coinciding with the disease becoming nationally notifiable in 2002 (Figure 1) (3034). For the first time in 10 years, giardiasis rates appear to be decreasing. Possible reasons for the decreased rates during 2011–2012 might include changes in transmission of disease caused by Giardia, a decreased emphasis on giardiasis surveillance in public health agencies, the 2011 change in case definition clarifying that clinical symptoms are necessary for categorizing giardiasis cases as confirmed, increased uptake of strategies to reduce waterborne transmission (e.g., implementation of EPA's Ground Water Rule to address contamination of public ground water systems (40), or a combination of these factors.

The last national surveillance data were published in 2009–2010 (34). Since publication of that data, rates have declined across all regions. Giardiasis rate reductions were most pronounced in the Midwest, where rates declined from 10.3 and 11.4 per 100,000 population in 2009 and 2010 to 6.6 and 5.8 in 2011 and 2012. As in previous years, rates were highest in northern states, and Vermont reported the highest rate for the last 7 years. The geographic differences might suggest actual regional differences in giardiasis transmission, or they might reflect variation in surveillance capacity across states. Although giardiasis is a nationally notifiable disease, six states did not report giardiasis during 2011–2012. The number of states that do not report giardiasis cases has increased from four to six states over the past 2 years (34). This represents the largest number of nonreporting states since giardiasis became nationally notifiable in 2002 (3134), which is a concerning trend, given that giardiasis is the most frequently identified enteric parasite in the United States (1). However, the nonreporting states do not explain the declines in national rates because rates declined in most states that consistently reported cases.

Giardiasis rates varied by age and sex. The rate of reported giardiasis was higher in males than females in almost all age groups, particularly among adults aged 45–49 years. Compared with previous years, giardiasis rates declined across most age groups and both sexes in 2011–2012. Among males and females, rates were highest among children aged 1–9 years, which is consistent with previously published reports (3034). Higher rates in children might be related to increased recreational water exposures, poor hygiene skills, close contact with other potentially infected children in child-care settings, and lack of previous exposure to Giardia, which could render them more susceptible to infection and illness (41,42). Giardia has been identified frequently as the cause of diarrhea among children examined in outpatient clinics (43), and transmission from ill children to household contacts has been documented in outbreak investigations (44,45). The sharpest declines were seen in this age group as well. The rate among children aged 1–4 years declined from 23.5 per 100,000 population in 2009–2010 to 16.4 in 2011–2012, and the rate among children aged 5–9 years dropped from 12.5 per 100,000 population in 2009–2010 to 8.4 in 2011–2012 (34). No national efforts to prevent person-to-person transmission in child-care settings have occurred that would explain the rate reductions in young children. Interventions to reduce drinking water-associated transmission of Giardia (e.g., EPA's Ground Water Rule) might have a larger impact on the young, because older persons have had more opportunities to be previously infected with Giardia, which could confer partial protection from reinfection or symptomatic infection (46,47). Reducing the presence of this parasite in the water might, in turn, prevent person-to-person transmission in settings that foster increased risk for infection, such as child-care centers (18,26).

During 2011–2012, a twofold increase in giardiasis reporting occurred during summer compared with winter months, with a peak in late July and early August. This finding is consistent with temporal patterns observed previously in the United States (3034) and Canada (41), and similar to the seasonal profile of other parasitic and bacterial enteric diseases (e.g., cryptosporidiosis and vibriosis) (48,49). The summer peak coincides with increased outdoor activities (e.g., camping and swimming) that likely increase exposure to contaminated water. Transmission associated with outdoor activities is facilitated by the substantial number of Giardia cysts that can be shed by a single person (17), the environmental hardiness of the organism (50), the extended periods of time that cysts can be shed (18), and the low infectious dose for infection (16).

Drinking water is a well-documented vehicle for Giardia transmission. G. intestinalis was the single most frequently identified pathogen in all drinking water outbreaks reported in the United States during 1971–2006, responsible for 28% of all outbreaks with an identified etiology (3). Untreated drinking water has been identified as a risk factor for sporadic giardiasis in the United States (51,52) and New Zealand (24). Groundwater can be particularly risky if acquired from poorly constructed or maintained wells that might have been subject to surface water contamination.

Both treated and untreated recreational water also have been implicated as vehicles of giardiasis transmission. During 1999–2008, Giardia was identified as a causal agent of eight (3.5%) of 228 reported recreational water-associated gastroenteritis outbreaks (53). In studies of sporadic giardiasis, swallowing water while swimming and recreational contact with fresh water were both risk factors for contracting Giardia (22,24). Giardia can be frequently detected in fecal material in pools (54), and transmission has been documented among diapered children who use swimming venues regularly (45,55,56).

Reported foodborne outbreaks of giardiasis have generally been caused by direct contamination by an infected food handler (57,58) or animal contamination of food (59). However, foodborne outbreaks of giardiasis are infrequently reported in the United States. During 2000–2010, <1% of foodborne outbreaks with an identified etiology was attributed to Giardia (59). Infections from contamination of widely distributed foods (e.g., fresh produce) might be difficult to detect. A recent study of Canadian produce showed that 1.8% of precut salad and leafy green samples were contaminated with Giardia (60), and a study of sporadic giardiasis in England identified eating lettuce as a risk factor for giardiasis (22). The use of reclaimed wastewater for irrigation is associated with the finding of Giardia cysts on fresh produce (61), highlighting the importance of using noncontaminated irrigation water to prevent foodborne disease.

Person-to-person transmission of Giardia also occurs. Persons attending or working in child-care settings or those who have close contact with persons with giardiasis are at increased risk for being infected (51,52,62,63). Exposure to feces through handling diapers and poor hygiene, particularly after toileting, in child-care settings might contribute to increased risk (20,55).

Although G. intestinalis infects both humans and animals, the role of zoonotic transmission to humans and the importance of animal contamination of food and water are being reexamined in light of advances in molecular epidemiology. Giardia has been detected in nearly all classes of vertebrates, including domestic animals and wildlife (64), but molecular characterization of G. intestinalis has identified relatively species-specific genetic assemblages. Humans are only infected with assemblages A and B, which can sometimes be found in other animals. However, animals are usually infected with other species-specific assemblages (64). Epidemiologic data implicating wildlife, cattle, and pets as sources of human-pathogenic Giardia assemblages are limited, and findings from molecular studies of G. intestinalis assemblages and subtypes suggest that the risk of zoonotic transmission is not as high as previously thought (15). No molecular data are reported to CDC surveillance systems, limiting the ability to understand the role of zoonotic transmission.

Strategies to reduce the incidence of giardiasis have focused on reducing waterborne and person-to-person transmission (Box). The low infectious dose of Giardia, protracted shedding of cysts, and moderate chlorine tolerance make it ideally suited for transmission through these pathways. The Environmental Protection Agency (EPA) enacted a series of rules designed to prevent pathogens in surface water sources from contaminating drinking water systems (65,66,67,68). These regulations might have contributed to a decrease in the number of giardiasis outbreaks associated with community drinking water systems (3). In 2006, EPA finalized the Ground Water Rule to address contamination of public ground water (well) systems, which is likely to reduce the number of groundwater-associated outbreaks of giardiasis (40). For recreational water, proper pool maintenance (i.e., sufficient disinfection, filtration, and recirculation of water) and excluding children with diarrhea from pools should decrease transmission through treated recreational water. Person-to-person transmission of Giardia is difficult to interrupt in a systematic fashion, particularly in child-care settings (63). Adherence to appropriate infection control policies (e.g., exclusion of children ill with diarrhea, hand washing, diaper changing, and separation of ill children from well children) is recommended for controlling giardiasis and other enteric pathogens in these group settings (69).

Limitations

The findings in this report are subject to at least five limitations. First, case reports lack data on exposure history and often have incomplete data on race and ethnicity; thus, it was not possible to evaluate the contributions of exposures or identify racial or ethnic groups at increased risk for giardiasis. Second, incomplete data on symptom onset date could have led to an inaccurate representation of the seasonal distribution of cases. Third, incidence of giardiasis is likely to be underestimated by these national surveillance data because of underreporting (e.g., not all persons infected with Giardia are symptomatic, persons who are symptomatic do not always seek medical care, health-care providers do not always include laboratory diagnostics in their evaluation of nonbloody diarrheal diseases, and case reports are not always completed for positive laboratory results or forwarded to public health officials). Fourth, the 2011 case definition clarification that symptoms should be present for a case to be confirmed might limit direct rate comparisons with previous years. Finally, giardiasis is not a reportable disease in all states, which can lead to an incomplete picture of its geographic distribution and an underestimation or overestimation of national incidence rates.

Future Directions

Although giardiasis is the most common enteric parasitic infection in the United States, gaps in understanding of its epidemiology still exist. Methods to improve reporting include encouraging health-care providers to consider and specifically request testing for Giardia in the workup of gastrointestinal illness, and encouraging health-care providers and laboratories to improve reporting of cases to jurisdictional health departments. Improved case investigations, geospatial studies, serosurveys, and the use of molecular tools would enhance understanding of the epidemiology of giardiasis. The majority of data on giardiasis transmission comes from outbreak investigations; however, the overwhelming majority of reported giardiasis cases occur sporadically. During 2011–2012, <2% of reported giardiasis cases was associated with outbreaks. Many giardiasis outbreaks associated with drinking water occur (3), but the relative contributions of waterborne, foodborne, person-to-person, and animal-to-person transmission are not well understood, especially for sporadic cases. Whether the geographic variability noted in this report reflects actual differences in transmission patterns and disease burden versus diagnosis and reporting artifacts is unclear; however, the sharp decline in rates in the Midwest is likely because of a regional decrease in transmission.

Future research is needed to help elucidate the sources of nonoutbreak associated giardiasis infections. Ecologic studies could characterize the potential contributions of private wells, septic systems, land application of biosolids (organic matter recycled from sewage), and agricultural operations in giardiasis transmission. Infected persons can shed Giardia for several weeks, and symptoms are variable; however, until recently, no reliable serologic assays for Giardia have been available, and no population studies of Giardia seroprevalence have been conducted. With recent laboratory advances (70), such studies might now be feasible and would contribute substantially to understanding of the prevalence of giardiasis in the United States. Enhanced genotyping methods would increase knowledge of the molecular epidemiology of Giardia, including elucidating the importance of zoonotic transmission. Molecular methods also could be used to assist public health officials in linking cases sharing common transmission routes, which could lead to increased outbreak detection. These tools, combined with traditional epidemiology and surveillance, would improve understanding of giardiasis risk factors and inform future prevention strategies. Although recent studies indicate a potential for chronic sequelae from giardiasis (9–14), additional research is needed to further improve understanding of the prevalence and scope of these conditions.

Conclusion

For the first time since 2002, giardiasis rates appear to be decreasing. Despite this decrease, giardiasis remains the most commonly reported intestinal parasitic infection in the United States. National surveillance data can be used to guide the revision, updating, and expansion of health communication efforts and other public health interventions to prevent and control giardiasis. Federal, state, and local health agencies can use giardiasis surveillance data to help elucidate the epidemiology of giardiasis in the United States, establish public health priorities for giardiasis prevention, target health communication messages, and design public health interventions to prevent the transmission of Giardia. Additional information about giardiasis is available at http://www.cdc.gov/parasites/giardia/.

Acknowledgments

This report is based, in part, on contributions by Michele C. Hlavsa, epidemiologist, Division of Foodborne, Waterborne, and Environmental Diseases, and jurisdiction surveillance coordinators Ruth Ann Jajosky, DMD, and Willie Anderson, Office of Surveillance, Epidemiology, and Laboratory Services, CDC.

References

  1. Kappus KD, Lundgren RG Jr, Juranek DD, Roberts JM, Spencer HC. Intestinal parasitism in the United States: update on a continuing problem. Am J Trop Med Hyg 1994;50:705–13.
  2. Wallender EK, Ailes EC, Yoder JS, Roberts VA, Brunkard JM. Contributing factors to disease outbreaks sssociated with untreated groundwater. Ground Water 2013.
  3. Craun GF, Brunkard JM, Yoder JS, et al. Causes of outbreaks associated with drinking water in the United States from 1971 to 2006. Clin Microbiol Rev 2010;23:507–28.
  4. Scallan E, Hoekstra RM, Angulo FJ, et al. Foodborne illness acquired in the United States—major pathogens. Emerg Infect Dis 2011;17:7–15.
  5. Collier SA, Stockman LJ, Hicks LA. Direct healthcare costs of selected diseases primarily or partially transmitted by water. Epidemiol Infect 2012;140:2003–13.
  6. Hellard ME, Sinclair MI, Hogg GG, Fairley CK. Prevalence of enteric pathogens among community based asymptomatic individuals. J Gastroenterol Hepatol 2000;15:290–3.
  7. Rodriguez-Hernandez J, Canut-Blasco A, Martin-Sanchez AM. Seasonal prevalences of Cryptosporidium and Giardia infections in children attending day care centres in Salamanca (Spain) studied for a period of 15 months. Eur J Epidemiol 1996;12:291–5.
  8. Eberhard M, Gabrielli A, Savioli L. Giardiasis (Giardia enteritis). In: Control of communicable diseases manual, 19th Edition. Heymann DL, Ed. Washington, DC; 2008:258–60.
  9. Cantey PT, Roy S, Lee B, et al. Study of nonoutbreak giardiasis: novel findings and implications for research. Am J Med 2011.
  10. D'Anchino M, Orlando D, De Feudis L. Giardia lamblia infections become clinically evident by eliciting symptoms of irritable bowel syndrome. J Infect 45:169–72.
  11. Di Prisco MC, Hagel I, Lynch NR, et al. Possible relationship between allergic disease and infection by Giardia lamblia. Ann Allergy 1993;70:210–3.
  12. Wensaas KA, Langeland N, Hanevik K, et al. Irritable bowel syndrome and chronic fatigue 3 years after acute giardiasis: historic cohort study. Gut 2012;61:214–9.
  13. Wensaas KA, Langeland N, Rortveit G. Post-infectious gastrointestinal symptoms after acute Giardiasis. A 1-year follow-up in general practice. Fam Pract 2010;27:255–9.
  14. Tupchong M, Simor A, Dewar C. Beaver fever—a rare cause of reactive arthritis. J Rheumatol 1999;26:2701–2.
  15. Xiao L, Fayer R. Molecular characterisation of species and genotypes of Cryptosporidium and Giardia and assessment of zoonotic transmission. Int J Parasitol 2008;38:1239–55.
  16. Rendtorff RC. The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules. Am J Hyg 1954;59:209–20.
  17. Danciger M, Lopez M. Numbers of Giardia in the feces of infected children. Am J Trop Med Hyg 1975;24:237–42.
  18. Pickering LK, Woodward WE, DuPont HL, Sullivan P. Occurrence of Giardia lamblia in children in day care centers. J Pediatr 1984;104:522–6.
  19. The Medical Letter, Inc. Giardiasis. In: Abramowicz M, editor. Drugs for parasitic infections. New Rochelle, NY: The Medical Letter; 2007.
  20. Hoque ME, Hope VT, Kjellstrom T, Scragg R, Lay-Yee R. Risk of giardiasis in Aucklanders: a case-control study. Int J Infect Dis 2002;6:191–7.
  21. Huang DB, White AC. An updated review on Cryptosporidium and Giardia. Gastroenterol Clin North Am 2006;35:291–314, viii.
  22. Stuart JM, Orr HJ, Warburton FG,et al. Risk factors for sporadic giardiasis: a case-control study in southwestern England. Emerg Infect Dis 2003;9:229–33.
  23. Ekdahl K, Andersson Y. Imported giardiasis: impact of international travel, immigration, and adoption. Am J Trop Med Hyg 2005;72:825–30.
  24. Snel SJ, Baker MG, Kamalesh V, French N, Learmonth J. A tale of two parasites: the comparative epidemiology of cryptosporidiosis and giardiasis. Epidemiol Infect 2009;137:1641–50.
  25. Staat MA, Rice M, Donauer S, et al. Intestinal parasite screening in internationally adopted children: importance of multiple stool specimens. Pediatrics 2011:e613–22:
  26. Cordell RL. The risk of infectious diseases among child care providers. J Am Med Womens Assoc 2001;56:109–12.
  27. Clinical and Laboratory Standards Institute. Procedures for the recovery and identification of parasites from the intestiinal tract; approved guideline. 2nd ed.: Clinical Laboratory Standards Institute; 2005.
  28. van Gool T, Weijts R, Lommerse E, Mank TG. Triple faeces test: an effective tool for detection of intestinal parasites in routine clinical practice. Eur J Clin Microbiol Infect Dis 2003;22:284–90.
  29. Garcia LS, Shimizu RY, Novak S, Carroll M, Chan F. Commercial assay for detection of Giardia lamblia and Cryptosporidium parvum antigens in human fecal specimens by rapid solid-phase qualitative immunochromatography. J Clin Microbiol 2003;41:209–212.
  30. Furness BW, Beach MJ, Roberts JM. Giardiasis surveillance—United States, 1992–1997. MMWR Surveill Summ 2000 Aug;49:1–13.
  31. Hlavsa MC, Watson JC, Beach MJ. Giardiasis surveillance—United States, 1998–2002. MMWR Surveill Summ 2005;54:9–16.
  32. Yoder JS, Beach MJ. Giardiasis surveillance—United States, 2003–2005. MMWR Surveill Summ 2007;56:11–8.
  33. Yoder JS, Harral C, Beach MJ. Giardiasis surveillance—United States, 2006-2008. MMWR Surveill Summ 2010;59:15–25.
  34. CDC. Giardiasis surveillance—United States, 2009–2010. MMWR Surveill Summ 2012;61:13–23.
  35. CDC. Giardiasis: 1997 case definition. Atlanta, GA: US Department of Health and Human Services, CDC; 1997. Available at http://wwwn.cdc.gov/nndss/script/casedef.aspx?CondYrID=683&DatePub=1997-01-01.
  36. CDC. Giardiasis: 2011 case definition. Atlanta, GA: US Department of Health and Human Services, CDC; 2011. Available at http://wwwn.cdc.gov/nndss/script/casedef.aspx?CondYrID=685&DatePub=1/1/2011.
  37. CDC. Summary of notifiable diseases— United States, 2011. MMWR Morb Mortal Wkly Rep 2013;60:1–117.
  38. US Census Bureau. Annual estimates of the population for the United States, regions, states, and Puerto Rico: April 1, 2010 to July 1, 2012. Washington, DC: US Census Bureau; 2012. Available at http://www.census.gov/popest/data/state/totals/2012/index.html.
  39. US Census Bureau. Census regions and divisions of the United States. Washington, DC: US Census Bureau. Available at http://www.census.gov/geo/maps-data/maps/pdfs/reference/us_regdiv.pdf.
  40. EPA. National primary drinking water regulations: Ground Water Rule, Volume 71, Number 216 (2006).
  41. Greig JD, Michel P, Wilson JB, et al. A descriptive analysis of giardiasis cases reported in Ontario, 1990–1998. Can J Public Health 2001;92:361–5.
  42. Naumova EN, Chen JT, Griffiths JK, et al. Use of passive surveillance data to study temporal and spatial variation in the incidence of giardiasis and cryptosporidiosis. Public Health Rep 2000:436–47.
  43. Caeiro JP, Mathewson JJ, Smith MA, et al. Etiology of outpatient pediatric nondysenteric diarrhea: a multicenter study in the United States. Pediatr Infect Dis J 1999;18:94–7.
  44. Katz DE, Heisey-Grove D, Beach M, Dicker RC, Matyas BT. Prolonged outbreak of giardiasis with two modes of transmission. Epidemiol Infect 2006;134:935–41.
  45. Polis MA, Tuazon CU, Alling DW, Talmanis E. Transmission of Giardia lamblia from a day care center to the community. AmJ Pub Health 1986;76:1142–4.
  46. Istre GR, Dunlop TS, Gaspard GB, Hopkins RS. Waterborne giardiasis at a mountain resort: evidence for acquired immunity. Am J Pub Health 1984;74:602–4.
  47. Singer S. Immunology of giardiasis. In: Luján H, Svärd S, editors. Giardia: Springer Vienna; 2011:319–31.
  48. CDC. Cryptosporidiosis surveillance—United States, 2009–2010. MMWR Surveill Summ 2012 ;61:1–12.
  49. Newton A, Kendall M, Vugia DJ, Henao OL, Mahon BE. Increasing rates of vibriosis in the United States, 1996–2010: review of surveillance data from 2 systems. Clin Infect Dis 2012;54 Suppl 5:S391–5.
  50. Erickson MC, Ortega YR. Inactivation of protozoan parasites in food, water, and environmental systems. J Food Prot 2006;69:2786–808.
  51. Dennis DT, Smith RP, Welch JJ, et al. Endemic giardiasis in New Hampshire: a case-control study of environmental risks. J Infect Dis 1993;167:1391–5.
  52. Chute CG, Smith RP, Baron JA. Risk factors for endemic giardiasis. Am J Pub Health 1987;77:585–7.
  53. Hlavsa MC, Roberts VA, Anderson AR, et al. Surveillance for waterborne disease outbreaks and other health events associated with recreational water—United States, 2007–2008. MMWR Surveill Summ 2011;60:1–32.
  54. Shields JM, Gleim ER, Beach MJ. Prevalence of Cryptosporidium spp. and Giardia intestinalis in swimming pools, Atlanta, Georgia. Emerg Infect Dis 2008;14:948–50.
  55. Ang LH. Outbreak of giardiasis in a daycare nursery. Commun Dis Public Health 2000;3:212–3.
  56. Harter L, Frost F, Grunenfelder G, Perkins-Jones K, Libby J. Giardiasis in an infant and toddler swim class. American J Pub Health 1984;74:155–6.
  57. Budu-Amoako E, Greenwood SJ, Dixon BR, Barkema HW, McClure JT. Foodborne illness associated with Cryptosporidium and Giardia from livestock. J Food Prot 2011;74:1944–55.
  58. Smith HV, Caccio SM, Cook N, Nichols RA, Tait A. Cryptosporidium and Giardia as foodborne zoonoses. Vet Parasitol 2007;149:29–40.
  59. CDC. Foodborne outbreak online database. Atlanta, GA: US Department of Health and Human Services, CDC; 2012.
  60. Dixon B, Parrington L, Cook A, Pollari F, Farber J. Detection of Cyclospora, Cryptosporidium, and Giardia in ready-to-eat packaged leafy greens in Ontario, Canada. J Food Prot 2013;76:307–13.
  61. Amahmid O, Asmama S, Bouhoum K. The effect of waste water reuse in irrigation on the contamination level of food crops by Giardia cysts and Ascaris eggs. Int J Food Microbiol 1999;49:19–26.
  62. Sagebiel D, Weitzel T, Stark K, Leitmeyer K. Giardiasis in kindergartens: prevalence study in Berlin, Germany, 2006. Parasitol Res 2009;105:681–7.
  63. Steketee RW, Reid S, Cheng T, et al. Recurrent outbreaks of giardiasis in a child day care center, Wisconsin. American J Pub Health 1989;79:485–90.
  64. Thompson RC. The zoonotic significance and molecular epidemiology of Giardia and giardiasis. Vet Parasitol 2004;126:15–35.
  65. US Environmental Protection Agency. Drinking water; national primary drinking regulations; filtration, disinfection; turbidity, Giardia lamibia, viruses, Legionelia, and heterotrophic bacteria; final rule, Vol. 54, No. 124. 40 CFR Parts 141 and 142. Washington, DC: Federal Register; 1989.
  66. US Environmental Protection Agency. Drinking water; national primary drinking regulations: Interim Enhanced Surface Water Treatment; final rule, Vol. 63, No. 241. 40 CFR Parts 141 and 142. Washington, DC: Federal Register; 1998.
  67. US Environmental Protection Agency. National primary drinking water regulations: Long Term 1 Enhanced Surface Water Treatment Rule, Vol. 67, No 9. 40 CFR Parts 9, 141, and 142. Federal Register; 2002.
  68. US Environmental Protection Agency. National Primary Drinking Water Regulations: Long Term 2 Enhanced, Surface Water Treatment Rule, Vol. 71, No 3. 40 CFR Parts 9, 141, and 142. Federal Register; 2006.
  69. Pickering LK, Bartlett AV, Woodward WE. Acute infectious diarrhea among children in day care: epidemiology and control. Rev Infect Dis 1986;8:539–47.
  70. Priest JW, Moss DM, Visvesvara GS, et al. Multiplex assay detection of immunoglobulin G antibodies that recognize Giardia intestinalis and Cryptosporidium parvum antigens. Clin Vaccine Immunol 2010;17:1695–707.

TABLE 1. Number, percentage,* and incidence rate of giardiasis case reports, by region, state, and territory — National Notifiable Diseases Surveillance System, United States, 2011–2012

United States

2011

2012

No.

%

Rate

No. of outbreak cases

No.

%

Rate

No. of outbreak cases

Northeast

4,888

29.0

8.8

28

4,365

28.7

7.8

40

Connecticut

233

1.4

6.5

223

1.5

6.2

Maine

171

1.0

12.9

169

1.1

12.7

4

Massachusetts

758

4.5

11.5

698

4.6

10.5

New Hampshire

131

0.8

9.9

106

0.7

8.0

New Jersey

437

2.6

4.9

423

2.8

4.8

New York State§

1,144

6.8

10.2

6

975

6.4

8.7

20

New York City§

917

5.4

11.1

872

5.7

10.5

Pennsylvania

795

4.7

6.2

22

658

4.3

5.2

16

Rhode Island

79

0.5

7.5

58

0.4

5.5

Vermont

223

1.3

35.6

183

1.2

29.2

Midwest

4,434

26.3

6.6

45

3,934

25.8

5.8

15

Illinois

407

2.4

3.2

8

347

2.3

2.7

Indiana

331

2.0

5.1

2

227

1.5

3.5

6

Iowa

271

1.6

8.8

251

1.7

8.2

Kansas

139

0.8

4.8

133

0.9

4.6

Michigan

550

3.3

5.6

547

3.6

5.5

5

Minnesota

672

4.0

12.6

610

4.0

11.3

Missouri

344

2.0

5.7

330

2.2

5.5

Nebraska

180

1.1

9.8

195

1.3

10.5

North Dakota

54

0.3

7.9

64

0.4

9.1

3

Ohio

799

4.7

6.9

18

582

3.8

5.0

1

South Dakota

110

0.7

13.4

11

144

1.0

17.3

Wisconsin

577

3.4

10.1

6

504

3.3

8.8

South

3,281

19.5

5.2

158

2,950

19.4

4.6

108

Alabama

171

1.0

3.6

178

1.2

3.7

Arkansas

123

0.7

4.2

108

0.7

3.7

Delaware

34

0.2

3.7

24

0.2

2.6

District of Columbia

56

0.3

9.0

77

0.5

12.2

Florida

1,255

7.4

6.6

129

1,095

7.2

5.7

108

Georgia

651

3.9

6.6

544

3.6

5.5

Kentucky

NR

NR

Louisiana

226

1.3

4.9

224

1.5

4.9

Maryland

291

1.7

5.0

24

239

1.6

4.1

Mississippi

NR

NR

North Carolina

NR

NR

Oklahoma

NR

NR

South Carolina

117

0.7

2.5

5

128

0.8

2.7

Tennessee

NR

NR

Texas

NR

NR

Virginia

295

1.8

3.6

274

1.8

3.3

West Virginia

62

0.4

3.3

59

0.4

3.2

Northwest

1,372

8.1

9.4

13

1,247

8.2

8.5

22

Alaska

101

0.6

14.0

96

0.6

13.1

Idaho

178

1.1

11.2

6

153

1.0

9.6

19

Montana

87

0.5

8.7

68

1.5

6.8

Oregon

436

2.6

11.3

6

381

2.5

9.8

1

Washington

529

3.1

7.8

512

3.4

7.4

Wyoming

41

0.2

7.2

1

37

0.2

6.4

2

Southwest

2,809

16.7

4.8

7

2,701

17.7

4.6

15

Arizona

133

0.8

2.1

113

0.7

1.7

California

1,750

10.4

4.6

1,725

11.3

4.5

6

Colorado

445

2.6

8.7

7

356

2.3

6.9

1

Hawaii

38

0.2

2.8

34

0.2

2.4

Nevada

79

0.5

2.9

91

0.6

3.3

New Mexico

108

0.6

5.2

95

0.6

4.6

1

Utah

256

1.5

9.1

287

1.9

10.1

7

Total United States

16,784

99.5

6.5

251

15,197

99.8

5.8

200


TABLE 1. (Continued) Number, percentage,* and incidence rate of giardiasis case reports, by region, state, and territory — National Notifiable Diseases Surveillance System, United States, 2011–2012

United States

2011

2012

No.

%

Rate

No. of outbreak cases

No.

%

Rate

No. of outbreak cases

Territory

Guam

-

2

<0.1

1.1

Puerto Rico

84

0.5

2.3

24

0.2

0.7

Total territories

84

0.5

2.2

0

26

0.2

0.7

0

Total

16,868

100.0

6.4

251

15,223

100.0

5.8

200

Abbreviation: NR = not reportable.

Sources: Population estimates are from the U.S. Census Bureau. Table 1. Annual estimates of the population for the United States, regions, states, and Puerto Rico: April 1, 2010 to July 1, 2012. Data in this table were accessed on November 9, 2013 at http://www.census.gov/popest/data/state/totals/2012/. Estimates of the New York City population: annual estimates of the resident population for incorporated places over 50,000, ranked by July 1, 2012, population: April 1, 2010 to July 1, 2012. Data in this table were accessed on November 9, 2013 at http://www.census.gov/popest/data/cities/totals/2012/index.html. Estimates for the population of Guam are from the International Data Base (IDB) Data Access. Data in this table were accessed on January 9, 2014 at http://sasweb.ssd.census.gov/cgi-bin/broker.

* Percentages might not total 100% because of rounding.

Cases per 100,000 population.

§ New York State and New York City data are mutually exclusive.


TABLE 2. Number and percentage* of giardiasis cases, by selected patient demographic characteristics — National Notifiable Diseases Surveillance System, United States, 2011–2012

Characteristic

No.

%

Sex

Male

18,437

57.7

Female

13,354

41.8

Missing

190

0.6

Total

31,981

100.0

Race

Alaska Native/American Native

119

0.4

Asian Pacific Islander

1,690

5.3

Black

2,179

6.8

White

13,737

43.0

Other

1,076

3.4

Missing

13,180

41.2

Total

31,981

100.0

Ethnicity

Hispanic

2,074

6.5

Non-Hispanic

14,516

45.4

Missing

15,391

48.1

Total

31,981

100.0

* Percentages might not total 100% because of rounding.


BOX. CDC recommendations to prevent and control giardiasis

Practice good hygiene.

  • Everywhere
    • Wet hands with clean, running water and apply soap. Lather all surfaces of hands and scrub for at least 20 seconds. Rinse with clean, running water and dry with a clean towel or air
      • before preparing or eating food,
      • after using the toilet,
      • after changing diapers or cleaning up a child who has used the toilet,
      • before and after caring for someone who is sick with diarrhea,
      • after touching an animal or animal waste,
      • after gardening, even if wearing gloves.

Note: It is unknown whether alcohol-based hand sanitizers effectively kill Giardia.

Information about handwashing is available from CDC at http://www.cdc.gov/handwashing/when-how-handwashing.html.

  • At child-care facilities
    • Exclude children who are ill with diarrhea from child-care settings until the diarrhea has stopped.
    • Wash hands before water-based activities like water tables.
  • At the pool
    • Protect others by not swimming if ill with diarrhea.
    • Do not swallow the water.
    • Take young children on bathroom breaks every 60 minutes.

Information about healthy swimming is available from CDC at http://www.cdc.gov/healthywater/swimming/protection/steps-healthy-swimming.html.

Avoid drinking water that might be contaminated.

  • Do not drink untreated water from lakes, rivers, springs, ponds, streams, or shallow wells.
  • Follow advice given during local drinking water advisories.
  • If the safety of drinking water is in doubt (e.g., during an outbreak or if water treatment is unknown), use at least one of the following:
    • bottled water.
    • water that has been previously boiled for 1 minute and left to cool. At elevations above 6,500 feet (1,981 meters), boil for 3 minutes.
    • a filter designed to remove Giardia
      • The label might read certified to "NSF 53" or "NSF 58".
      • Filter labels that read "absolute pore size of 1 micron or smaller" are also effective.

Information about water filters is available from CDC at http://www.cdc.gov/parasites/crypto/gen_info/filters.html.

  • If the safety of drinking water is in doubt (e.g., during an outbreak or if water treatment is unknown), use bottled, boiled, or filtered water to wash fruits and vegetables that will be eaten raw.

Practice extra caution when traveling.

  • Do not use or drink inadequately treated water or use ice when traveling in countries where the water might be unsafe.
  • Avoid eating uncooked foods when traveling in countries where the food supply might be unsafe.

Information about how to prevent illnesses while traveling is available from CDC at http://wwwnc.cdc.gov/travel/content/safe-food-water.aspx.

Prevent contact with feces during sex.

  • Use barriers (e.g., condoms, natural rubber latex sheets, dental dams, or cut-open non-lubricated condoms) between the mouth and a partner's genitals or rectum.
  • Wash hands immediately after handling a condom or other barrier used during anal sex and after touching the anus or rectal area.

Information about giardiasis prevention and control is available at http://www.cdc.gov/parasites/giardia/prevent.html.


FIGURE 1. Incidence rate* of giardiasis, by year and case classification — National Notifiable Diseases Surveillance System, United States, 1993–2012

This bar graph presents the incidence rate of giardiasis, by year and case classification during the years 1993-2012.

* Cases per 100,000 population.

N = 423,450.

§ Nonconfirmed includes probable, suspect, and unknown cases.

First full year of reporting.

Alternate Text: This bar graph presents the incidence rate of giardiasis, by year and case classification during the years 1993-2012.


FIGURE 2. Incidence rate* of giardiasis, by reporting jurisdiction — National Notifiable Diseases Surveillance System, United States, 2012

This U.S. map presents the incidence rate of giardiasis, by reporting jurisdiction (state and U.S. territories) during the year 2012.

* Cases per 100,000 population.

Not a reportable disease in these states.

§ New York State and New York City data are mutually exclusive.

Alternate Text: This U.S. map presents the incidence rate of giardiasis, by reporting jurisdiction (state and U.S. territories) during the year 2012.


FIGURE 3. Number* of cases per year and average annual incidence rate of giardiasis, by age group — National Notifiable Diseases Surveillance System, United States, 2011–2012

This bar graph presents the number of cases per year and average annual incidence rate of giardiasis during 2011-2012

* N = 31,167; age for 814 patients was unknown.

Cases per 100,000 population.

Alternate Text: This bar graph presents the number of cases per year and average annual incidence rate of giardiasis during 2011-2012


FIGURE 4. Average annual incidence rate* of giardiasis, by sex and age group — National Notifiable Diseases Surveillance System, United States, 2011–2012

This line graph presents the annual incidence rate of giardiasis according to age group and sex, during the years 2011-2012.

* Cases per 100,000 population.

N = 30,997; age and sex for 1,094 patients was unknown.

Alternate Text: This line graph presents the annual incidence rate of giardiasis according to age group and sex, during the years 2011-2012.


FIGURE 5. Number* of giardiasis case reports, by date of symptom onset — National Notifiable Diseases Surveillance System, United States, 2011–2012

This line graph presents the number of case reports of giardiasis, by date of onset of symptoms, during 2011-2012.

* Of total number of cases (N = 31,981), date of onset for 14,876 patients was unknown.

Alternate Text: This line graph presents the number of case reports of giardiasis, by date of onset of symptoms, during 2011-2012.



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