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The Highlights section presents information on the public health importance of selected nationally notifiable and non-notifiable diseases, including a) domestic and 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 1997 national total of 127 confirmed or probable California serogroup viral encephalitis cases (all of which were La Crosse encephalitis cases) is the fourth largest yearly total of such cases reported since 1964. The 73 case reports from West Virginia (57% of the national total) represent that state's largest total and an increase of 11% over its 1996 total. Much of the increase in reports from West Virginia may be attributable to this state's recent implementation of an active surveillance system for this disease. La Crosse encephalitis is endemic in the eastern United States, where it is associated with exposure to deciduous forests and Aedes triseriatus (the eastern treehole mosquito). A summertime/autumnal outbreak of St. Louis encephalitis in central Florida accounted for nine of the 13 cases reported nationally in 1997. The last major epidemic of St. Louis encephalitis in the United States (223 cases and 11 deaths) occurred in Florida in 1990. St. Louis encephalitis affects persons in portions of both the eastern and western United States. In Florida, the primary mosquito vector of St. Louis encephalitis virus is Culex nigripalpus. Fourteen cases of eastern equine encephalitis among humans were reported in 1997 from the South (12 cases), New England (one case), and the Upper Midwest (one case). Eastern equine encephalitis virus is typically transmitted to humans by various Aedes mosquito species. No cases of western equine encephalitis among humans have been reported nationally since 1994. The primary mosquito vector of western equine encephalitis virus in the western United States is Culex tarsalis.
National reporting for cryptosporidiosis began in 1995 with 2,972 cases reported from 27 states. During 1996, as cryptosporidiosis became a reportable disease in an increased number of states, 2,426 cases were reported from 42 states. In 1997, a total of 2,566 cases were reported from 45 states. Because the diagnosis of cryptosporidiosis is often not considered, and because laboratories do not routinely test for Cryptosporidium infection, cryptosporidiosis continues to be underdiagnosed and underreported.
Four cases of diphtheria were reported in the United States in 1997; two persons, both with localized mild illness, had culture-confirmed diphtheria. One confirmed case was caused by infection with a toxigenic strain of Corynebacterium diphtheriae, and was reported from a known endemic focus in South Dakota (MMWR 1997;46:506-10); one case caused by nontoxigenic C. diphtheriae was reported from Oregon. Two probable cases were reported from Nevada. Both case-patients had acute membranous pharyngitis; oropharyngeal specimens were positive for diphtheria toxin by polymerase chain reaction, but bacterial cultures of these specimens were negative. In 1997, more than 7,000 cases of diphtheria were reported in an ongoing diphtheria epidemic in the New Independent States of the former Soviet Union. No importations were reported in the United States.
In 1997, a total of 260 cases of Haemophilus influenzae (Hi) invasive disease among children aged less than 5 years were reported. (Data were provided by the National Immunization Program and were based on date of onset, not MMWR week.) An estimated 20,000 cases of Haemophilus influenzae type b (Hib) invasive disease among children occurred annually prior to Hib vaccine licensure in 1987. (JAMA 1993;269:221-6) The dramatic decline is attributed to the widespread administration of the Hib vaccine to preschool-aged children. Of the 260 cases, 201 (77%) isolates were serotyped, and 82 (41%) of the isolates for which serotype was known were type b. Of the 82 cases of Hib invasive disease reported in children aged less than 5 years, 42 (51%) were aged less than 6 months, which is too young to have completed a three-dose primary Hib vaccination. However, 27 (68%) of the 40 children who were old enough (aged greater than or equal to 6 months) to have completed a three-dose primary series before they developed Hib invasive disease were incompletely vaccinated or their vaccination status was unknown. These cases might have been prevented with age-appropriate vaccination.
In 1997, a total of 21 cases of Hantavirus pulmonary syndrome (HPS) were reported. HPS is a pan-American viral zoonosis caused by Sin Nombre virus and other New World hantaviruses, which in the United States, include Bayou virus, Black Creek Canal virus, and New York-1 virus. The identified rodent reservoirs for Sin Nombre, New York-1, Black Creek Canal, and Bayou viruses are, respectively, Peromyscus maniculatus (deer mouse), Peromyscus leucopus (white-footed mouse), Sigmodon hispidus (cotton rat), and Oryzomys palustris (rice rat). Cases of HPS have been found in the continental United States, Canada, Argentina, Brazil, Chile, Paraguay, and Uruguay. As of March 31, 1998, national surveillance for HPS has identified 179 confirmed cases in 29 states (case-fatality ratio = 44.7%).
Post-diarrheal hemolytic uremic syndrome (HUS) is a life-threatening illness characterized by hemolytic anemia, thrombocytopenia, and renal injury. Nearly all cases in the United States are caused by infection with Shiga toxin-producing Escherichia coli, with serotype O157:H7 being predominant. In 1997, the second year of national reporting, 20 states reported 93 cases of post-diarrheal HUS to CDC. By comparison, 18 states reported 104 cases in 1996. The median age of patients was 4 years (range: 1-89 years), with females accounting for 62% of patients overall. Illness was seasonal, with 50% of cases occurring during July through September.
In 1996, the Advisory Committee on Immunization Practices (ACIP) issued recommendations for the prevention of hepatitis A through active or passive immunization (MMWR 1996;45[No. RR-15]). The report provides recommendations for use of the hepatitis A vaccines (i.e., HAVRIX , manufactured by SmithKline Beecham Biologicals, and VAQTA , manufactured by Merck & Company, Inc.). For communities with high rates of hepatitis A and periodic outbreaks (peak rates: 700 reported cases per 100,000 population), routine vaccination of children aged 2 years and catch-up vaccination of older children is recommended. To control outbreaks in communities with intermediate rates of hepatitis A (i.e., 50-200 reported cases per 100,000 population), vaccination programs targeting subpopulations with the highest rates of disease may be considered. In these communities, ongoing routine vaccination of young children should be implemented to prevent future outbreaks.
Hepatitis C virus (HCV) infection is the most common bloodborne infection in the United States. Based on data from the CDC Sentinel Counties Study of Viral Hepatitis, it is estimated that as many as 180,000 new HCV infections occurred each year during the 1980s. Since 1989, the annual number of new infections has declined by 80%. However, in 1996, data from the third National Health and Nutrition Examination Survey, conducted from 1988 through 1994, indicated that approximately 4 million Americans (1.8%) are infected with HCV. Many of these chronically infected persons might not be aware of their infection or be clinically ill, because symptoms of hepatitis C-related chronic liver disease might not develop for 10-20 years after infection. However, such persons can infect others and are at risk for chronic liver disease or other HCV-related chronic diseases. Cirrhosis develops in 10%-20% of persons with HCV-related chronic hepatitis during the first two decades after infection, and 8,000-12,000 persons die from HCV-related chronic liver disease each year. CDC recently published new guidelines for HCV prevention and control (MMWR 1998;47[No. RR-19]).
In 1997, reports based on AIDS surveillance data indicated substantial declines in perinatally acquired AIDS, reflecting declining perinatal HIV transmission. HIV surveillance data indicated that the increasing use of zidovudine was temporally associated with this substantial decline in perinatally acquired AIDS (MMWR 1997;46:1086-92). These data demonstrate success in nationwide efforts to implement Public Health Service guidelines for use of zidovudine to reduce perinatal HIV transmission (MMWR 1994;43[No. RR-11]); MMWR 1998;47[No. RR-2]) and routine, voluntary prenatal HIV testing (MMWR 1995;44[No. RR-7]). States that conduct surveillance of perinatally exposed and infected children can evaluate the impact of the guidelines more completely and document resources needed to care for perinatally exposed infants. In 1997, a total of 30 states conducted surveillance of HIV infection in children, reporting 258 HIV-infected children who had not progressed to AIDS and 200 children who had AIDS. These states also received 2,238 new reports of perinatally exposed children who required follow up with health-care providers to determine their HIV infection status.
A total of 138 laboratory-confirmed cases of measles were reported to CDC in 1997, which is the lowest number of measles cases reported in one year and is less than half the previous record low. Of the 138 cases reported, 57 (41%) were international importations, and exposure to these cases resulted in 17 (12%) additional cases. Thus, 74 (54%) cases were associated with importation. An additional seven cases had virologic evidence suggesting an imported measles virus. Fifty-four (41%) measles patients were aged less than 5 years, 39 (28%) were aged 5-19 years, and 42 (30%) were aged greater than or equal to 20 years. Thirty-two patients (23%) reported having been vaccinated; seven (5%) received two doses. A total of 13 outbreaks were reported, with the largest involving eight cases. In 1997, no confirmed measles cases were reported from 21 states, and fewer than five cases were reported from 20 states and the District of Columbia.
In 1997, four plague cases among humans were reported in the United States (two cases in California, one in Arizona, and one in Colorado). One case was fatal and, like two fatal cases that occurred in 1996, septicemic plague was diagnosed postmortem. Each of these cases, which occurred in plague-endemic areas, illustrates the need for health-care providers to maintain a high level of awareness about the risks of human plague. Of the 350 cases reported in the United States from 1970 through 1997, approximately 80% were reported from the southwestern states of New Mexico, Arizona, and Colorado; 9% were reported from California; and nine other western states reported limited numbers of cases. Plague also occurs in animal populations in four other western states that have not reported cases among humans, including Kansas, where Yersinia pestis-infected prairie dog fleas were identified in 1997. This is the first report of plague in an animal in Kansas since 1950; however, a nearby county in Oklahoma experienced one case among a person in 1991, and other Great Plains states have reported epizootic activity in recent years (MMWR 1994;43:242-6). Internationally, outbreaks of rat-associated plague occurred in the port city of Mahajanga, Madagascar from 1995 through 1997. These are the first port-related outbreaks to be reported from that country in decades. Researchers reported the first case of multidrug-resistant Y. pestis in 1997. This isolate, which was obtained in 1995 from a case in Madagascar, contained a plasmid that conferred resistance to antibiotics commonly prescribed for plague treatment or prophylaxis (e.g., streptomycin, chloramphenicol, and tetracycline) (N Engl J Med 1997;337:677-80, 702-4).
In 1997, the Advisory Committee on Immunization Practices (ACIP) recommended a change in routine childhood vaccination policy for polio in the United States. The previously recommended schedule of four doses of attenuated oral poliovirus vaccine (OPV) was changed to a sequential schedule of two doses of inactivated poliovirus vaccine (IPV) followed by two doses of OPV for routine vaccination of children. Since 1980, a total of 147 cases have been reported, of which 139 were associated with the use of OPV. The last imported case was reported in 1993.
According to reports from active surveillance programs in five states (i.e., California, Connecticut, Georgia, Minnesota, and Oregon), the incidence of invasive group A streptococcal disease during 1997 was 4.1 cases/100,000 population; disease incidence ranged from 2.2 to 5.1 cases/100,000 population among the surveillance areas. Streptococcal toxic shock syndrome and necrotizing fasciitis accounted for approximately 6.9% and 7.7% of invasive cases, respectively. Overall case-fatality among patients with invasive group A streptococcal disease was 13%; case-fatality rates were higher among patients with streptococcal toxic shock syndrome and necrotizing fasciitis (43% and 21%, respectively). Risk factors for invasive group A streptococcal disease include elderly age, HIV infection, diabetes, cancer, alcohol abuse, and varicella infection.
The proportion of drug-resistant Streptococcus pneumoniae isolates continues to increase, according to reports from active surveillance programs in seven states (i.e., California, Connecticut, Georgia, Maryland, Minnesota, Oregon, and Tennessee). During 1997, approximately 26% of pneumococcal isolates obtained from sterile sites were no longer susceptible to penicillin (mean inhibitory concentration [MIC] greater than or equal to 0.1 ug/mL). In 1997, the proportion of all isolates with high-level penicillin resistance (MIC greater than or equal to 2 ug/mL), increased from 12% in 1996 to 14.4%; a total of 7.2% of isolates had MICs greater than or equal to 4 ug/mL compared with 5.4% in 1996. The resistant proportion varied widely by geographic region. To limit the contribution of unnecessary antimicrobial use to the spread of drug-resistant S. pneumoniae, CDC and the American Academy of Pediatrics issued recommendations for judicious use of antimicrobial agents for upper-respiratory-tract infections among children (Pediatrics 1998;101[suppl]). Educational materials concerning the principles of judicious antimicrobial use can be obtained by calling the National Center for Infectious Diseases at (404) 639-4702 for an order form.
Fifty cases of tetanus were reported in 1997. During 1995-1997, an average annual incidence of 41 cases were reported, the lowest ever reported since national tetanus surveillance began in 1947. The average annual incidence of 0.15 cases per million population represents a slight decline from the incidence of 0.2 cases per million population reported during 1991-1994.
In 1997, several outbreaks of cyclosporiasis associated with various types of fresh produce (e.g., raspberries, mesclun lettuce, and basil) occurred in the United States. In the largest outbreak, which was associated with consumption of fresh raspberries, 41 clusters with a total of 762 cases (25% were laboratory confirmed) were reported by 13 states, the District of Columbia, and one province in Canada.
Fifty-six laboratory-positive cases of dengue were imported into the United States in 1997 and diagnosed at the CDC Dengue Branch. This number represents a 30% increase from the number of laboratory-confirmed cases reported in 1996 (n=43). Similarly, the total number of dengue and dengue hemorrhagic fever (DHF) cases reported by Pan American Health Organization member countries in 1997 (n=364,945) was 46% higher than the 1996 total (n=250,707). Autochthonous dengue cases (n=3) were documented in south Texas again in 1997, underscoring the risk of dengue transmission in southern gulf coast states where mosquito vectors occur. After a 15-year absence, dengue cases were reported from Cuba in 1997. The municipality of Santiago de Cuba experienced an outbreak with 2,946 laboratory-diagnosed cases and 205 DHF cases, which resulted in 12 deaths.
In June 1997, HIV-infection reporting for adults (i.e., persons aged greater than or equal to 13 years) was added to the list of nationally notifiable diseases at a Council of State and Territorial Epidemiologists (CSTE) meeting. During 1997, reports based on acquired immunodeficiency syndrome (AIDS) surveillance data highlighted substantial declines in AIDS incidence and deaths. As a result of improvements in treatment and care of persons infected with the human immunodeficiency virus (HIV), surveillance of AIDS alone no longer accurately reflects the magnitude or direction of the epidemic. Data concerning persons in whom HIV infection is diagnosed before AIDS is diagnosed are needed to determine populations that could benefit from prevention and treatment services. CSTE recommends that all states and territories implement confidential HIV infection reporting based on methods that provide accurate and representative data for all persons confidentially diagnosed with HIV infection.
In May 1997, the first known case of disease among humans caused by influenza A (H5N1) virus occurred in a previously healthy 3-year-old child in Hong Kong; this child died from his illness. An additional 17 cases (including five deaths) were detected in November and December 1997. All cases occurred coincident withoutbreaks of highly pathogenic avian influenza A (H5N1) virus among poultry. At the end of December, Hong Kong authorities initiated the slaughter of all chickens in Hong Kong and, since then, no additional cases of influenza A (H5N1) virus have been detected among humans despite enhanced surveillance. The pandemic potential of influenza A (H5N1) viruses remains unknown. No cases of H5N1 infection were reported in the United States.
Tularemia was removed from the nationally notifiable disease list in 1995. However, as of January 1998, a total of 36 states maintained tularemia as a notifiable condition. Based on a telephone survey of state departments of health conducted from 1995 through 1997, a total of 313 cases of tularemia were reported by 43 states (119 cases in 1995, 89 cases in 1996, and 105 cases in 1997). Of these, 155 (49%) were reported from Missouri, Oklahoma, Kansas, and Arkansas.
The magnitude and impact of vancomycin-resistant enterococci (VRE) in the United States are demonstrated by CDC's National Nosocomial Infections Surveillance (NNIS) system, which includes more than 275 U.S. hospitals. Additional data are available on the Internet at http://www.cdc.gov/ncidod/hip/Surveill/surveill.htm. During 1989-1997, the percentage of enterococci resistant to vancomycin isolated from patients in intensive care units with nosocomial infections increased from 0.4% to 23.2% (Table). The percentage of VRE isolated from patients in noncritical care units with nosocomial infections increased from 0.3% to 15.4%.
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