Giardiasis NNDSS Summary Report for 2019

Background

Surveillance Overview: National Giardiasis Case Surveillance

Screenshot of Giardiasis Summary Report 2019 PDF

Giardiasis is an illness caused by the protozoan parasite Giardia duodenalis (formerly called G. lamblia or G. intestinalis), which causes gastrointestinal symptoms such as diarrhea, abdominal cramps, bloating, weight loss, or malabsorption (1, 2). Each year in the United States, it is estimated that Giardia causes more than 1.1 million illnesses (3).

Giardiasis is a nationally notifiable disease; the first full year of reporting was 1993. National data are collected through passive surveillance. Healthcare providers and laboratories that diagnose confirmed giardiasis cases report to the local or state health departments. State and territorial health departments, the District of Columbia (DC), and the New York City health departments, in turn, voluntarily notify CDC of cases via the National Notifiable Disease Surveillance System (NNDSS). The number of health departments submitting can vary from year to year depending on which states have designated giardiasis as reportable in their jurisdictions.

State, DC, US territory, and freely associated state public health agencies voluntarily notify CDC of giardiasis outbreaks via the National Outbreak Reporting System (NORS). NORS data are not presented here; however, summaries of data on waterborne disease outbreaks are published elsewhere.

Methods

Case Definition

The definition of a confirmed case of giardiasis has changed over time; the first national case definition was published in 1997 (4), and a revised case definition was published in 2011 (5). The current (2011) case definition differs from the 1997 definition in clarifying that clinical symptoms are necessary for categorizing giardiasis cases as confirmed.

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 (5). 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. A national case definition for suspected cases of giardiasis does not exist; the definition varies by state. Cases not classified as confirmed, probable, or suspect are classified as unknown.

Analysis

National giardiasis surveillance data for 2019 were analyzed using R version 4.0.3. Data cleaning processes included case deduplication and the verification of case status (e.g., confirmed, nonconfirmed). Numbers, percentages, and incidence (cases per 100,000 population) of giardiasis were calculated in aggregate for the United States and separately for each reporting jurisdiction. Rates were calculated by dividing the number of giardiasis cases by each year’s mid-year census estimates (6) and multiplying by 100,000. U.S. Census Bureau data were obtained using their Application Programming Interface and the R censusapi package (78). Region and total population estimates included only jurisdictions that reported (Supplemental Table 1). 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 (9). 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 were calculated by year (2010 to 2019) and case status (confirmed or nonconfirmed). Average annual giardiasis rates were calculated by demographic variables (e.g., age and sex) and jurisdiction. Rates were not calculated for race, ethnicity, or month of onset due to large proportion of missing data for these variables (i.e., 26.1%, 39.6%, and 40.1% respectively). Cases reported by territories were excluded from the analysis, because detailed demographic census data are not available to calculate rates by age and sex.

Acknowledgements

The authors gratefully acknowledge Kathleen E. Fullerton, Michelle Gleason, and Ariana Perez for their assistance in developing the annual reports of giardiasis by state through previous work on the Domestic Epidemiology Team, Waterborne Disease Prevention Branch, CDC. This report is based on contributions by state and local epidemiologists and microbiologists.

Tables and Figures

Figure 1. Incidence* of reported giardiasis cases, by year and case classification — National Notifiable Diseases Surveillance System, United States, 2010–2019 (N = 158,344)

* Cases per 100,000 population per year
§ Probable, suspect, and unknown cases


Since 2011, the incidence of reported, confirmed giardiasis cases has remained < 7.0 cases per 100,000 population. In 2019, there were 14,887 reported giardiasis cases in the United States (96.6% confirmed and 3.4% nonconfirmed).

Table 1. Number, percentage*, and incidence§ of reported giardiasis cases, by region and jurisdiction — National Notifiable Diseases Surveillance System, United States, 2019 (N = 14,887)

Number, percentage*, and incidence§ of cryptosporidiosis cases, by region and jurisdiction — National Notifiable Diseases Surveillance System, United States, 2018 (n=12,540)
Region/Jurisdiction No. % Incidence No. of outbreak-
associated cases
Northeast 4,229 28.4 7.6 109
Connecticut 188 1.3 5.3 N/A
Maine 142 1.0 10.6 N/A
Massachusetts 532 3.6 7.7 N/A
New Hampshire 97 0.7 7.1 N/A
New Jersey 436 2.9 4.9 N/A
New York State 1,018 6.8 9.2 11
New York City 1,202 8.1 14.4 92
Pennsylvania 536 3.6 4.2 6
Rhode Island 79 0.5 7.5 N/A
Vermont NR NR NR N/A
Midwest 3,118 20.9 5.6 10
Illinois NR NR NR N/A
Indiana 198 1.3 2.9 N/A
Iowa 269 1.8 8.5 N/A
Kansas 134 0.9 4.6 N/A
Michigan 423 2.8 4.2 N/A
Minnesota 574 3.9 10.2 10
Missouri 223 1.5 3.6 N/A
Nebraska 94 0.6 4.9 N/A
North Dakota 49 0.3 6.4 N/A
Ohio 424 2.8 3.6 N/A
South Dakota 92 0.6 10.4 N/A
Wisconsin 638 4.3 11.0 N/A
South 2,958 19.9 4.4 93
Alabama 160 1.1 3.3 N/A
Arkansas 132 0.9 4.4 N/A
Delaware 35 0.2 3.6 1
District of Columbia 75 0.5 10.6 N/A
Florida 1,088 7.3 5.1 89
Georgia 480 3.2 4.5 N/A
Kentucky NR NR NR N/A
Louisiana 256 1.7 5.5 N/A
Maryland 174 1.2 2.9 N/A
Mississippi NR NR NR N/A
North Carolina NR NR NR N/A
Oklahoma NR NR NR N/A
South Carolina 156 1.0 3.0 N/A
Tennessee NR NR NR N/A
Texas NR NR NR N/A
Virginia 300 2.0 3.5 1
West Virginia 102 0.7 5.7 2
Northwest 933 6.3 5.8 24
Alaska 76 0.5 10.4 N/A
Idaho 177 1.2 9.9 22
Montana 79 0.5 7.4 N/A
Oregon 284 1.9 6.7 1
Washington 288 1.9 3.8 1
Wyoming 29 0.2 5.0 N/A
Southwest 3,649 24.5 5.9 5
Arizona 143 1.0 2.0 N/A
California 2,603 17.5 6.6 N/A
Colorado 492 3.3 8.5 N/A
Hawaii 44 0.3 3.1 3
Nevada 85 0.6 2.8 N/A
New Mexico 88 0.6 4.2 N/A
Utah 194 1.3 6.1 2
Total 14,887 100 5.8 241

Abbreviation NR = Not Reportable

* Percentages might not total 100% because of rounding
§ Cases per 100,000 population
New York State and New York City data are mutually exclusive


By jurisdiction, giardiasis incidence ranged from 2.0 per 100,000 population in Arizona to 14.4 per 100,000 population in New York City. By region, incidence of reported giardiasis cases ranged from 4.4 cases per 100,000 population in the South to 7.6 cases per 100,000 population in the Northeast. Differences in incidence might reflect differences in risk factors or mode of transmission of Giardia; the magnitude of outbreaks; or the capacity or requirements to detect, investigate, and report cases.

Figure 2. Incidence* of reported giardiasis cases, by reporting jurisdiction§ — National Notifiable Diseases Surveillance System, United States, 2019 (N=14,887)

* Cases per 100,000 population
§ Non-reporting states included Illinois, Kentucky, Mississippi, North Carolina, Oklahoma, Tennessee, Texas, and Vermont
New York State and New York City data are mutually exclusive


Giardiasis is geographically widespread across the United States. Although incidence rates appear to be consistently higher in the northern states, differences in incidence might reflect differences in risk factors or modes of transmission of Giardia; the magnitude of outbreaks; or the capacity or requirements to detect, investigate, and report cases.

Table 2. Number and percentage* of reported giardiasis cases, by selected patient demographic characteristics — National Notifiable Diseases Surveillance System, United States, 2019 (N = 14,887)

Table 2. Number and percentage* of giardiasis cases, by selected patient demographic characteristics — National Notifiable Diseases Surveillance System, United States, 2018 (n = 15,579)
Characteristic No. %
Sex
Male 9,314 62.6
Female 5,513 37.0
Unknown 60 0.4
Race
American Indian or Alaska Native 78 0.5
Asian or Pacific Islander 470 3.2
Black 1,004 6.7
White 7,552 50.7
Other 1,894 12.7
Unknown 3,889 26.1
Ethnicity
Hispanic or Latino 1,322 8.9
Not Hispanic or Latino 7,673 51.5
Unknown 5,892 39.6
Total 14,887 100.0

* Percentages might not total 100% because of rounding


During 2019, a total of 9,314 patients were male (62.6%) and 5,513 (37.0%) were female; 60 (0.4%) were missing data on sex. The majority of cases for whom data on race were available occurred among the classifications white (68.7%), black (9.1%), and Asian/Pacific Islander (4.3%). Data on race were not included for 26.1% of total annual case reports, and data on ethnicity were missing for 39.6% of case reports. The majority of patients for whom data on ethnicity were available were non-Hispanic (85.3%).

Figure 3. Incidence* of reported giardiasis cases, by age group — National Notifiable Diseases Surveillance System, United States, 2019 (N = 14,845§)

Line graph of the incidence of giardiasis cases by age group

* Cases per 100,000 population
§ Age data missing for 42 patients


In 2019, the incidence of reported giardiasis cases was highest among patients aged under 5 years, 55-59 years, and 50-54 years (incidence = 6.1, 5.4, and 5.3 cases per 100,000 population, respectively).

Figure 4. Incidence* of reported giardiasis cases, by sex and age group — National Notifiable Diseases Surveillance System, United States, 2019 (N = 14,787§)

Line graphs of the incidence of giardiasis cases by age group and sex reported to CDC for 2019

* Cases per 100,000 population
§ Age or sex data missing for 100 patients


The highest incidence of giardiasis was among males ages 55–59 years (7.3 cases per 100,000 population) and females under 5 years (5.3 cases per 100,000 population). Rates were highest among males in every age group. The difference was most pronounced between sexes aged 25-29 years, with males presenting with 4.2 additional cases of giardiasis per 100,000 population compared to females.

Figure 5. Number of reported giardiasis cases, by date of symptom onset — National Notifiable Diseases Surveillance System, United States, 2019 (N = 8,910§)

§ Date of symptom onset data missing for 5,977 patients


In 2019, the majority of cases by symptom onset occurred between June and October, with a peak in July (n=1,038).

Supplemental Table 1. Giardiasis reporting and non-reporting states (gray shading) — National Notifiable Diseases Surveillance System, United States, 2010–2019

Chart displaying cases by year and cases reported for 1995 to 2019. The yearly incidence is the height of each bar. The scale for the yearly incidence, 0 to 15 cases per 100,000 population in one case per 100,000 population increments, is the y-axis. Each year of data, X-axis is from 1995 on the left to 2019 on the right in one year increments

Supplemental Figure 1. Incidence* of reported giardiasis cases, by year and case classification — National Notifiable Diseases Surveillance System, United States, 1995 –2019 (N = 480,921)

* Cases per 100,000 population per year
§ Probable, suspect, or unknown cases
First full year of national reporting

References
  1. Huang DB, White AC. An updated review on Cryptosporidium and Giardia. Gastroenterol Clin North Am. 2006;35(2):291-314, viii. DOI: https://www.sciencedirect.com/science/article/pii/S0889855306000252?via%3Dihubexternal icon
  2. Eberhard M, Gabrielli A, Montresor A, et al. Giardiasis (Giardia enteritis). In: Control of communicable diseases manual, 20th Edition. Heymann DL, Ed. Washington, DC; 2014:234-36.
  3. Collier SA, Deng L, Adam EA, et al. An Estimate of the Burden and Direct Healthcare Cost of Waterborne Disease in the United States. Emerg Infect Dis. 2021;27(1): 140-149. https://doi.org/10.3201/eid2701.190676external icon.
  4. 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.
  5. 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.
  6. U.S. Census Bureau. Demographic Characteristics Estimates by Age Groups –Vintage 2019 (Population: April 1, 2009 to July 1, 2019). Washington, DC: U.S. Census Bureau; Release Date: May 2020. Available at https://www.census.gov/data/developers/data-sets/popest-popproj/popest.html. Accessed using an Application Programming Interface on January 26, 2021.
  7. U.S. Census Bureau. Census Data API Discovery Tool. Washington, DC: U.S. Census Bureau; Release Date: February 21, 2017. Accessed at https://www.census.gov/data/developers/updates/new-discovery-tool.htmlexternal icon on January 13, 2021.
  8. Recht, H. censusapi: Retrieve Data from the Census APIs. R package version 0.7.1. 2020. Available on https://cran.r-project.org/web/packages/censusapi/index.htmlexternal icon.
  9. U.S. Census Bureau. Census regions and divisions of the United States. Washington, DC: U.S. Census Bureau. Available at https://www2.census.gov/geo/pdfs/maps-data/maps/reference/us_regdiv.pdf pdf icon[PDF – 2 Pages]external icon.