Current Trends Community Outbreaks of Shigellosis -- United States

From 1986 to 1988*, the reported isolation rate of Shigella in the United States increased from 5.4 to 10.1 isolates per 100,000 persons (Figure 1). In 1988, state health departments reported 22,796 isolates of Shigella to CDC, the highest number since national surveillance began in 1965. In addition to the recent increase in Shigella isolation rates, many communitywide shigellosis outbreaks that have been difficult to control have been reported. This report describes four community outbreaks of shigellosis during 1986-1989 in which innovative public health control measures were used.

Kankakee County, Illinois. From October 1986 through February 1987, an outbreak of shigellosis caused by S. sonnei occurred in Kankakee County, Illinois (population: 97,800). Of 191 persons with culture-confirmed shigellosis, 70% were black and 61% were aged 1-10 years. Thirty-one percent of patients were hospitalized. Cases were clustered in low-income areas. An epidemiologic investigation did not identify common sources of exposure in the community; many patients reported having had contact with persons with culture-confirmed shigellosis or symptoms compatible with shigellosis.

To control this outbreak, from December 12 to January 10 the following measures were implemented: 1) information about shigellosis and its prevention was provided to parents of all children in the school district where most of the cases occurred, to child-care centers and preschools, and through schools, churches, and the news media; 2) teachers monitored handwashing by students before lunch; 3) parents assisted in monitoring handwashing in schools in the most severely affected areas; and 4) home-prepared foods were not permitted at any school or child-care events. Although the number of reported cases subsequently decreased, the outbreak did not end until March.

Peoria County, Illinois. From February through September 1987, a shigellosis outbreak caused by S. sonnei occurred in Peoria County, Illinois (Figure 2) (population: 181,500). Of the 513 culture-confirmed cases, 75% were in blacks and 69% were in children aged 1-10 years. Most patients resided in low-income areas. Seven percent of patients were hospitalized. Investigation did not identify a common source of exposure; most patients had a history of contact with a person who had culture-confirmed shigellosis or symptoms compatible with shigellosis.

During April, the following interventions were implemented: 1) child-care center and nursery school employees were informed about shigellosis prevention; 2) school officials in the affected area ensured that warm water, soap, and disposable towels for handwashing were always available for students; 3) in schools, parents and teachers instructed students on proper handwashing and monitored children for symptoms of shigellosis; 4) printed educational material about shigellosis was provided to all persons attending Women, Infants, and Children (WIC) clinics, immunization clinics, community clinics, and hospital emergency rooms; 5) volunteers from the local Urban League and housing authority made door-to-door visits in affected neighborhoods to identify cases and provide printed educational material; 6) religious leaders discussed the Shigella outbreak with their congregations, and church publications included information on shigellosis prevention; and 7) parents taught neighborhood children how to wash their hands and monitored them for symptoms of shigellosis. Although the number of reported cases decreased concurrently with the intervention, the outbreak continued at a lower level until September.

Orange County, New York. From November 29, 1986, to February 28, 1987, 110 culture-confirmed cases of S. sonnei gastroenteritis were reported in residents of a religious community (population: 5200) in Orange County, New York (Figure 3). Cases occurred primarily among school children 2-1/2 - 9 years of age; cases were evenly distributed by sex. An epidemiologic investigation did not identify a point source of exposure; spread of disease was consistent with person-to-person transmission.

Control measures were focused in schools and implemented from January 12 through February 28. The measures included 1) widespread dissemination of information about shigellosis and its prevention (e.g., proper handwashing and diaper changing) in schools and the community child-care center, 2) a program in which older children monitored handwashing by young children in the schools, and 3) periodic health department sanitation inspections of the schools. The number of reported cases of shigellosis declined concurrently with the intervention efforts.

Caddo County, Oklahoma. From August through October 1989, 34 persons with gastroenteritis caused by S. sonnei were identified in Caddo County, Oklahoma (Figure 4) (population: approximately 32,100, including 18% Native Americans). Ninety-one percent of cases were in Native Americans. Seventy-one percent were in children and teenagers. An epidemiologic investigation did not identify a common source of infection but did suggest person-to-person transmission: 37 persons with symptoms compatible with shigellosis became ill after being exposed to a person (usually in their household) with a culture-confirmed Shigella infection. Clusters of cases occurred in persons residing in two Native American housing developments where children regularly played and ate snacks together.

Initial interventions implemented from August 29 to September 13 included 1) efforts to contact families of patients to identify potential exposures and secondary cases and to provide information on hygiene and handwashing, 2) education at child-care centers and other institutions on the importance of hygiene and sanitation in preventing transmission, and 3) encouragement of physicians, hospitals, and clinical laboratories in the area to assist in identifying and reporting new cases. The number of new cases reported initially declined; however, when new cases began to increase again, additional measures were implemented from September 26 to October 4, including dissemination of information on shigellosis and its prevention through 1) assistance of tribal leaders in providing information in tribal newsletters and at informal gatherings, 2) presentations at tribal senior citizen lunches, 3) house-to-house visits by public health officials and other persons in areas where clusters of cases were identified, 4) distribution of take-home handouts to students in child-care centers and schools, 5) press releases to local newspapers and radio stations, 6) puppet shows on handwashing performed at all child-care centers, where informational posters were distributed to attendees, and 7) notification to restaurants and churches of the importance of excluding symptomatic persons from food handling duties. The last confirmed case occurred on October 21. Reported by: C Pate, MS, D Safiran, F Sutton, N Scanlon, E Blanchette, Kankakee County Health Dept; A Kennell, MS, C Marvin, MS, L Esch, P Roberts, Peoria City/County Health Dept; K Kelly, C Langkop, MS, BJ Francis, MD, State Epidemiologist, Illinois Dept of Public Health. A Werzberger, MD, Monroe; S Kondracki, R Gallo, DL Morse, MD, State Epidemiologist, New York State Dept of Health. P Callahan, P Boden, MS, GR Istre, MD, State Epidemiologist, Oklahoma State Dept of Health. R Myers, Indian Health Service. Div of Field Svcs, Epidemiology Program Office; Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since 1986, the incidence of shigellosis in the United States has increased in all regions of the country. The highest isolation rates were reported among residents of counties with large proportions of low-income minority residents, among young children, and among women of childbearing age.

Communitywide outbreaks of shigellosis can be difficult to control because of the ease of person-to-person transmission among young children, high secondary attack rates, the frequently extended duration of these outbreaks, and multiple points of exposure. The impact of community interventions can be difficult to measure; however, the outbreaks described in this report suggest that effective control efforts should include the following: 1) communitywide recognition of the problem and participation in the intervention, 2) diversified and culture-specific educational efforts to promote handwashing and hygiene, and 3) supervised handwashing for children. Because community leaders can play a key role in developing interventions and ensuring that these interventions are accepted in the community, they should be actively involved in all control efforts.

Handwashing with soap and running water may be the single most important preventive measure to interrupt transmission of shigellosis (1). Soap and running water should be readily accessible to all persons during community outbreaks of shigellosis. Because young children are most likely to be infected with Shigella and are also most likely to infect others (2), a strict policy of supervised handwashing for young children after they have defecated and before they eat is crucial. Institutions where hygiene may be suboptimal (e.g., schools, child-care centers, and homeless shelters) can amplify transmission of shigellosis into the community and should be targeted for intensive control efforts. Excluding persons with diarrhea from handling food and limiting use of home-prepared foods at large gatherings will reduce the risk of large outbreaks caused by foodborne transmission.

Antimicrobials have a limited role in the control of epidemic shigellosis and are not a substitute for hygienic measures in reducing the secondary spread of shigellosis. Antimicrobials should be reserved for treatment of patients only when clinically indicated, and the decision to use antimicrobials to treat patients with mild, self-limiting illness should be weighed against the risk of producing resistant strains of Shigella (3). Prophylactic use of antimicrobials cannot be recommended to prevent illness in persons who are exposed but not ill. In addition, using antimicrobials to treat patients with mild shigellosis to reduce the spread of secondary infections is not known to be any more effective in preventing Shigella infections than handwashing with soap and water; moreover, this practice can lead to the development of resistant strains that complicate therapy (4,5). Because resistance patterns may change, antimicrobial selection should be based on ongoing monitoring of local antimicrobial resistance of Shigella strains.

Shigellosis outbreaks can occur at any time of the year but are most common in the summertime (6). Shigella infections should be suspected in communitywide (Continued on page 519)epidemics of diarrheal illness that disproportionately affect young children. Stool specimens should be obtained and state and local health departments informed promptly of culture-confirmed cases so that outbreaks of shigellosis can be recognized and appropriate control measures instituted.

References

1. Kahn MU. Interruption of shigellosis by handwashing. Trans R Soc Trop Med Hyg 1982;76:164-8.

2. Wilson R, Feldman RA, Davis J, LaVenture M. Family illness associated with Shigella infection: the interrelationship of age of the index patient and the age of household members in acquisition of illness. J Infect Dis 1981;143:130-2.

3. Weissman JB, Gangarosa EJ, Dupont HL. Shigellosis: to treat or not to treat? JAMA 1974;229:1215-6.

4. CDC. Multistate outbreak of Shigella sonnei gastroenteritis--United States. MMWR 1987;36:440-2,448-9.

5. Griffin PA, Tauxe RT, Redd SC, Puhr ND, Hargrett-Bean N, Blake P. Emergence of highly trimethoprim-sulfamethoxazole resistant Shigella in a Native American population: an epidemiologic study. Am J Epidemiol 1989;129:1042-51.

6. Black RE, Craun GF, Blake PA. Epidemiology of common-source outbreaks of shigellosis in the United States, 1961-1975. Am J Epidemiol 1978;108:47-52. *The most recent year for which national surveillance data are available.

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