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The Highlights section presents information on the public health importance of selected nationally notifiable diseases, including a) domestic and some international disease outbreaks, b) active surveillance findings, c) changes in data reporting practices, d) the impact of prevention programs, e) the emergence of antimicrobial resistance, and f) changes in immunization policies. This information is intended to provide a context in which to interpret surveillance and disease-trend data and to provide further information on the epidemiology and prevention of selected diseases.
The annual incidence of acquired immunodeficiency syndrome (AIDS) and deaths among persons with AIDS declined during 1996, reflecting the beneficial impact of newly available therapies. Although this trend continued through 1998, provisional data for 1999 suggest that the number of AIDS cases and deaths might be leveling. Before the widespread availability of effective treatments, AIDS surveillance data were representative of underlying trends in human immunodeficiency virus (HIV) transmission. Because of changes in the epidemiology of AIDS associated with treatment successes, AIDS incidence no longer accurately reflects HIV incidence trends. AIDS data now reflect a combination of factors, including a) variation in HIV transmission patterns over a long period, b) differences in access to and use of testing and treatment among populations who are at risk or infected, and c) treatment regimens that might be failing because of drug resistance and poor adherence.
To provide better data for HIV prevention efforts, CDC and the Council of State and Territorial Epidemiologists (CSTE) have recommended that national surveillance expand to include both HIV infection and AIDS cases (MMWR 1999;48[RR-13] (Requires Adobe Acrobat Reader - available here.); CSTE position statement ID-4, 1997). An integrated national HIV/AIDS surveillance system would provide information regarding persons in whom HIV infection has been newly diagnosed, persons with severe HIV disease (AIDS), and those dying of HIV disease. Currently, at the local level, 33 states and 1 U.S. territory report HIV infections by the patient's name, 6 states and 1 U.S. territory use codes provided by health-care providers for HIV reporting, and 2 states convert names to codes after a report is received.
In 1999, a total of 143 cases of chancroid was reported to CDC, for a rate of 0.1 cases/100,000 population. The number of cases reported in 1999 represent a 24.3% decline from 1998 and a continuing decline since 1987. However, chancroid is difficult to culture and could be substantially underdiagnosed. Several studies that have used DNA amplification tests (which are not commercially available) have identified this infection in cities where it was previously undetected (J Infect Dis 1998;178:1795-8).
In 1999, a total of 656,721 cases of genital chlamydial infection was reported to CDC, for a rate of 254.1 cases/100,000 population. This is the highest rate of chlamydial infection reported to CDC since voluntary case reporting began in the mid-1980s. It is also the highest rate since genital chlamydial infection became a nationally notifiable disease in 1995. This increase is primarily caused by the continued expansion of chlamydia screening programs and the increased use of more sensitive diagnostic tests for this condition. Since the late 1980s, data on chlamydia prevalence obtained by monitoring test positivity rates of persons screened in different clinic settings have generally documented declining levels of infection in many parts of the United States (CDC. Sexually transmitted disease surveillance 1999 supplement: Chlamydia Prevalence Monitoring Project. November 2000).
During 1995-1999, a total of 53 laboratory-confirmed cases of cholera, all caused by Vibrio cholerae O1, was reported to CDC. Twenty-nine (53%) patients were hospitalized, and one died. Thirty-six (68%) infections were acquired outside the United States, whereas four (8%) were acquired through consumption of contaminated seafood harvested in Gulf Coast waters. Among travel-associated cholera cases, 32% of isolates were resistant to trimethoprim-sulfamethoxazole, sulfisoxazole, streptomycin, and furazolidone. Thus, foreign travel and contaminated seafood continue to account for most cholera cases in the United States, and antimicrobial resistance is increasing among V. cholerae O1 strains isolated from ill travelers.
In 1999, no probable or confirmed cases of toxigenic Corynebacterium diphtheriae were reported in the United States. However, one man aged 75 years who had visited a nondairy cattle farm 2 weeks earlier died of an illness clinically consistent with respiratory diphtheria. A toxigenic strain of C. ulcerans was isolated from a throat swab from the patient. C. ulcerans is primarily an animal pathogen, but can be toxigenic and cause fatal or nonfatal clinical respiratory diphtheria in humans.
In 1999, a total of 360,076 cases of gonorrhea was reported to CDC, for a rate of 133.2 cases/100,000 population. This was a 9.2% increase over the 1997 rate (122.0/100,000) and a 1.2% increase over the 1998 rate (131.6/100,000). Possible reasons for this trend include expansion of screening programs (motivated by the availability of simultaneous testing for genital chlamydial infections), increased use of new diagnostic tests with improved sensitivity, improvements in surveillance systems, and true increases in morbidity in some geographic areas and segments of the population.
In 1999, a total of 261 cases of Haemophilus influenzae (Hi) invasive disease among children aged <5 years was reported (data was provided by the National Immunization Program and were based on date of onset, not MMWR week). Before a vaccine was introduced in 1987, approximately 20,000 cases of H. influenzae type b (Hib) invasive disease occurred among children annually (JAMA 1993;269:221-6). Because of widespread use of the Hib vaccine among preschool-aged children, the number of Hib cases has declined sharply. Of the 261 cases reported during 1999, a total of 215 (82%) Hi isolates were serotyped, and 71 (33%) of these were type b. Among the 71 cases of Hib invasive disease reported among children aged <5 years, 30 (42%) were among those aged <6 months, which is too young to have completed a three-dose primary Hib vaccination. However, 23 (56%) of the 41 children who were old enough (i.e., aged greater than or equal to 6 months) to have completed a three-dose primary series either had unknown vaccination status (3 children) or were incompletely vaccinated (20 children). These cases might have been prevented with age-appropriate vaccination.
In 1999, a total of 42 probable cases of hantavirus pulmonary syndrome (HPS) from 15 states was reported to CDC's National Center for Infectious Diseases; of the 33 cases that were laboratory confirmed by CDC, 10 (30%) were fatal. CDC also confirmed two case-patients with hantavirus infection that did not develop into HPS. Since surveillance began in 1993, cases of HPS have been reported from Canada, Argentina, Paraguay, Brazil, Uruguay, Chile, and Bolivia. Cases with onset in 1999 were retrospectively recognized from Panama, the first Central American country to report HPS. HPS is caused by several hantaviruses in the Western Hemisphere, and most have specific sigmodontine rodent reservoirs of the family Muridae. Although most HPS in the United States is caused by Sin Nombre virus and its variants (i.e., New York and Monongahela), some cases have been associated with other hantaviruses, including Bayou and Black Creek Canal. Virus is shed in rodent urine, feces, and saliva, then transmitted through inhalation.
Postdiarrheal hemolytic uremic syndrome (HUS) is a life-threatening illness characterized by hemolytic anemia, thrombocytopenia, and renal injury. In the United States, most cases are caused by infection with Escherichia coli O157:H7 or other Shiga toxin-producing E. coli. In 1999, the fourth year of national reporting, 26 states reported 181 cases of postdiarrheal HUS to CDC. The median age of patients was 4 years (range: <1-93), and 58% of patients were female. Illness was seasonal, with 54% of cases occurring during June-September.
By comparison, 17 states reported 119 cases in 1998, and 20 states reported 93 cases in 1997. Although the number of areas reporting and the number of cases reported increased in 1999, eight states and at least one territory did not list HUS as a notifiable disease in 1999, contributing to substantial underreporting.
Routine childhood hepatitis A vaccination is recommended in the 11 states where the average annual hepatitis A rate during 1987-1997 was greater than or equal to 20 cases/100,000 population (i.e., approximately twice the national average). Routine childhood vaccination should be considered in the six states where the average rate during 1987-1997 was at least 10 cases/100,000 population, but <20/100,000 population.
The overall rate of hepatitis A reported during 1999 was the lowest recorded. However, because hepatitis A rates tend to vary from year to year and from region to region, determining whether this low rate is caused by routine immunization or the natural variability in infection rates is impossible. Monitoring the incidence of hepatitis A to determine if these low rates are sustained over time is critical to assessing the impact of routine vaccination.
Reported cases of acute hepatitis B have decreased >60% during the past decade, from 21,102 cases in 1990 to 7,694 cases in 1999. Surveillance data are being used to monitor the impact of the national strategy for eliminating hepatitis B virus (HBV) infection. Healthy People 2010 objectives call for a 75-90% reduction in the national incidence of hepatitis B among adults (baseline: 15-24 cases/100,000 persons), a 99% reduction among children aged 2-18 years (baseline: 945 cases/year), and a 75% reduction in the number of perinatal HBV infections (baseline: 1,682 infections/year). Reported hepatitis B cases can be used to monitor the occurrence of disease among adults. However, because most infections among infants and young children are asymptomatic, reported cases underestimate the incidence of disease in these age groups. Thus, data from other sources (e.g., serosurveys) are needed to monitor progress toward eliminating HBV transmission among younger age groups.
Cases of hepatitis C reported to the National Notifiable Disease Surveillance System (NNDSS) are considered unreliable because a) there is no serologic marker for acute infection and b) most health departments do not have the resources to determine if a positive laboratory report for hepatitis C virus (HCV) infection represents acute infection, chronic infection, repeated testing of a person previously reported, or a false-positive result. Historically, the most reliable national estimates of acute disease incidence have come from sentinel surveillance. After adjusting for underreporting and asymptomatic infections, the annual number of new infections has decreased >80% since 1989 to 38,000 cases in 1997 (CDC, unpublished data, 1999). Because surveillance for acute hepatitis C provides the best means to evaluate the effectiveness of preven tion efforts and identify missed opportunities for prevention, efforts are underway to help states improve and establish surveillance.
In 1998-1999, reports based on AIDS data indicated that the recent decline in AIDS cases and deaths was slowing. Because of improvements in treatment and care of persons infected with HIV, these data could represent a) persons whose treatment was unsuccessful, b) persons who were not tested for HIV before developing AIDS, or c) persons who did not seek or have access to testing and treatment earlier. Public health officials need data concerning persons in whom HIV infection was diagnosed before AIDS to determine who could benefit from prevention and treatment services. In June 1997, reporting of HIV infection among adults and adolescents (i.e., persons aged greater than or equal to 13 years) was added to the list of nationally notifiable diseases at the annual CSTE meeting. CSTE recommended that all states and U.S. territories implement confidential HIV infection reporting based on methods that provide accurate and representative data for all persons diagnosed confidentially. Recommendations for implementing national HIV case surveillance were published in December 1999, and the revised surveillance case definition became effective January 1, 2000. Currently, 33 states and the U.S. Virgin Islands have implemented confidential reporting of HIV among adults and adolescents as an extension of current AIDS surveillance.
In 1999, AIDS surveillance data indicated continued, substantial declines in perinatally acquired AIDS, reflecting declines in perinatal HIV transmission. HIV surveillance data indicated that the increasing use of zidovudine by mothers and newborns was temporally associated with this decline, demonstrating success in nationwide efforts to implement Public Health Service guidelines for routine, voluntary prenatal HIV testing (MMWR 1995;44[No. RR-7]) (Requires Adobe Acrobat Reader - available here.) and the use of zidovudine to reduce perinatal HIV transmission (MMWR 1998;47[RR-2]). Requires Adobe Acrobat Reader - available here.
States that conduct surveillance for perinatally exposed and infected children aged <13 years can evaluate the impact of the guidelines and document resources needed to care for perinatally exposed infants. In 1999, a total of 33 states and the U.S. Virgin Islands conducted surveillance for HIV infection among children, reporting 233 children whose infection had not progressed to AIDS and 123 children who had AIDS. These states also received 2,004 new reports of perinatally exposed children who required follow-up with health-care providers to determine their HIV infection status. Recommendations for implementing a national HIV case surveillance were published in December 1999, and the revised surveillance case definition became effective January 1, 2000. Enhanced programmatic and surveillance efforts to further reduce perinatal HIV transmission are underway.
In 1999, approximately 16,273 cases of Lyme disease were reported to CDC. Most cases continue to be reported from the northeastern and north-central United States. CDC promotes community-based prevention of Lyme disease using a combination of strategies aimed at reducing vector tick densities, preventing human exposure to infected vector ticks, and vaccinating persons aged 15-70 years when appropriate. A model prevention project is underway in a community in Connecticut. CDC plans to expand prevention projects to other endemic areas.
In 1999, a total of 100 confirmed cases of measles was reported. Thirty-one states and the District of Columbia reported no confirmed measles cases. Forty-two case-patients were aged <5 years, 26 were aged 5-19 years, and 32 were aged greater than or equal to 20 years. Eleven outbreaks (range: 3-15 cases) were reported. Of the 100 cases reported, 33 were imported from outside the United States, and exposure to these case-patients caused 33 additional cases. The remaining 34 cases were of unknown source. Genotypic analysis of isolated measles viruses in seven chains of transmission showed no evidence of an endemic strain (MMWR 2000:49:557-60). In 1999, CDC convened a panel of expert consultants to review the information on measles epidemiology, molecular virology, surveillance quality, and population immunity in the United States. The experts concluded that measles is not currently endemic in the United States. Because of the continued threat of imported measles, high population immunity must be maintained to continue low levels of transmission.
Since 1980, the number of reported cases of pertussis has increased in the United States. The reasons for this rise are unknown, but could include increased awareness of pertussis among health-care providers, increased use of more sensitive diagnostic tests, and better reporting of cases to health departments. Of 7,288 cases reported during 1999, a total of 27% occurred among children aged <7 months, who were too young to have received the recommended three doses of a pertussis-containing vaccine; 11% were among preschool-aged children (i.e., those aged 1-4 years); and 28% were among children aged 10-19 years. Since 1995, the coverage rate with at least three doses of a pertussis-containing vaccine has been 95% among U.S. children aged 19-35 months (MMWR 2000;49:585-9). Because vaccine-induced immunity wanes approximately 5-10 years after pertussis vaccination, adolescents can become susceptible to disease. Since 1990, the incidence of pertussis among preschool-aged children has not changed, but the incidence among adolescents has increased in some states (Clin Inf Dis 1999;28:1230-7).
A sequential schedule of inactivated poliovirus vaccine (IPV) and live, attenuated oral poliovirus vaccine (OPV) (i.e., two doses of IPV followed by two doses of OPV) was introduced in 1997 for routine childhood polio vaccination in the United States. Since implementation of this schedule, five cases of vaccine-associated paralytic poliomyelitis (VAPP) with onset in 1997 and two cases with onset in 1998 have been confirmed. Three of these cases were associated with administration of the first or second dose of OPV to children who had not previously received IPV, and one of the 1998 cases was associated with the third dose of OPV. Before the sequential schedule, the average annual number of VAPP cases was eight, which suggests that VAPP has declined since introduction of the sequential schedule. Continued monitoring with additional observation time is required to confirm these preliminary findings because of potential delays in reporting. Further reductions are expected because the Advisory Committee on Immunization Practices (ACIP) has approved an all-IPV schedule beginning January 2000, which is intended to eliminate the risk for VAPP.
During the 1990s, rubella cases declined substantially in the United States, from 1,125 reported cases in 1990 to 267 reported cases in 1999. Since 1997, approximately 19 rubella outbreaks have occurred in the United States, mostly among persons born in countries that do not have routine rubella vaccination programs or that have only recently implemented such programs. During the 1990s, <10 cases of congenital rubella syndrome have been reported annually; most cases were among infants born to mothers born outside the United States.
Shigella sonnei infections continue to account for most shigellosis in the United States. Prolonged, communitywide outbreaks of S. sonnei infections that are transmitted in child care centers and other settings where maintenance of good hygienic conditions requires special care account for much of the problem. S. sonnei can also be transmitted through contaminated foods and through water used for drinking or recreational purposes.
In 1999, approximately 10,200 cases of invasive group A streptococcal (GAS) disease and 1,200 deaths occurred nationally, according to reports from the Active Bacterial Core Surveillance (ABCs) project under CDC's Emerging Infections Program. This program operates in eight states (California, Connecticut, Georgia, Maryland, Minnesota, New York, Oregon, and Tennessee). During 1999, the incidence of this disease was 3.8 cases/100,000 population. Rates were highest among children aged <1 year (4.6 cases/100,000) and adults aged greater than or equal to 65 years (9.2 cases/100,000). Streptococcal toxic- shock syndrome and necrotizing fasciitis accounted for approximately 3.4% and 6.0% of invasive cases, respectively. The overall case-fatality rate among patients with invasive GAS disease was 11.8%. CDC identifies invasive GAS isolates based on sequences of the variable portion of the M-protein gene (i.e., emm typing); 9.3% of the 645 GAS isolates submitted and emm typed in 1999 were newly recognized emm types.
In 1999, the ABCs project of CDC's Emerging Infections Program collected information on invasive pneumococcal disease, including drug-resistant Streptococcus pneumoniae, in eight states (California, Connecticut, Georgia, Maryland, Minnesota, New York, Oregon, and Tennessee). Of the 3,745 S. pneumoniae isolates collected, 10.3% exhibited intermediate resistance to penicillin (minimum inhibitory concentration [MIC] 0.1-1 ug/mL), and 16.7% were fully resistant (MIC greater than or equal to 2 ug/mL). For cefotaxime, 11.1% of all isolates had intermediate resistance and 5.9% were resistant. For erythromycin, 20.7% were resistant. Nearly 1 in 5 (18%) isolates were not susceptible to greater than or equal to 3 classes of drugs commonly used to treat pneumococcal infections. In February 2000, the U.S. Food and Drug Administration licensed a pneumococcal conjugate vaccine for use in infants and young children. Information is available on the Internet at <http://www.fda.gov/cber/products/pneuled021700.htm>. Among isolates from children aged <5 years reported to ABCs during 1999, a total of 76.7% of all strains (n=977) and 81.4% of strains not susceptible to penicillin (n=370) were serotypes included in this 7-valent vaccine.
In 1999, a total of 556 cases of congenital syphilis was reported to CDC, for a rate of 14.3 cases/100,000 live births. Like primary and secondary syphilis, the rate of congenital syphilis has declined sharply in recent years, from a peak of 107.3/100,000 in 1991. Congenital syphilis persists in the United States because a substantial number of women don't receive syphilis serologic testing until late in their pregnancy or not at all. This lack of screening is often related to a lack of prenatal care or late prenatal care (MMWR 1999;48:757-61).
In 1999, a total of 6,657 primary and secondary syphilis cases was reported to CDC. During 1990-1998, the primary and secondary syphilis rate declined 88%, from 20.3 cases/100,000 population to 2.5/100,000. This is the lowest level since reporting began in 1941. Although syphilis has declined in all regions of the United States and in all racial/ethnic groups, rates remain disproportionately high in the South and among non-Hispanic blacks, and focal outbreaks continue to occur, including recent outbreaks among men who have sex with men.
In 1999, a total of 40 cases of tetanus was reported. Five (12.5%) cases were among persons aged <25 years, 22 (55.0%) were among persons aged 25-59 years, and 13 (32.5%) were among persons aged >59 years. The percentage of cases among persons aged 25-59 years has increased during the last decade; previously, most cases were among persons aged >59 years. Seven of the cases among persons aged 25-59 years were reported in intravenous drug users; two of these cases were fatal. Two cases were in children (aged 4 and 5 years) who had never been vaccinated against tetanus because of their parents' philosophic objection to vaccination.
In 1999, a total of 17,531 tuberculosis (TB) cases (rate: 6.4 cases/100,000 population) was reported to CDC from all states and the District of Columbia. This is a 5% decrease from 1998 and a 34% decrease from 1992, when cases peaked during the resurgence of TB in the United States. During 19921999, TB cases among U.S.-born persons decreased 49%, whereas cases among foreign-born persons increased 4%. Since 1993, when states began reporting initial drug susceptibility results to CDC, the number of multidrug-resistant TB (MDR TB) cases among persons with no history of TB decreased from >400 (2.5%) to <150 (1.1%).
These declines appear to be the result of successful efforts to strengthen TB control after the resurgence of TB and the emergence of MDR TB. The relatively stable number of cases reported among foreign-born persons supports the inference that most cases are caused by infection with Mycobacterium tuberculosis in the person's country of origin. CDC has collaborated with state and local health departments to publish recommendations for enhancing TB control efforts among foreign-born persons and is working with these jurisdictions to expand current efforts based on these recommendations (MMWR 1998;47[No. RR-16]). Requires Adobe Acrobat Reader - available here.
In 1999, typhoid fever was diagnosed in 346 persons in the United States. Despite the availability of effective vaccines, NNDSS reports 300-400 cases each year. Approximately 80% of these cases occur among persons who report international travel during the preceding 6 weeks. Persons traveling to and from their country of origin appear to be at high risk (JAMA 2000;283:2668-73). In many areas of the world, Salmonella Typhi strains have acquired resistance to multiple antimicrobial agents, including ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole (JAMA 2000;283:2668-73).
In 1995, varicella vaccine was licensed in the United States. During 1999, vaccine coverage among children aged 19-35 months was 59%. Although varicella is not a nationally notifiable disease, seven states maintained adequate levels of reporting by reporting varicella cases constituting greater than or equal to 5% of their birth cohort during 1990-1995. Although the number of reported cases varied annually, the number declined steadily in these states during 1997-1999. The marked decline in reported cases in 1999 is consistent with data from active varicella surveillance (in which attenuation of seasonality and marked decline in reported cases occurred in 1999) and is suggestive of vaccine impact (CDC, unpublished data, 2000). Ongoing surveillance will be important to monitor impact of the varicella vaccination program.
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