Shigellosis

In January 1991, the Lexington-Fayette County (Kentucky) Health Department (LFCHD) received three reports of Shigella sonnei infections from the University of Kentucky microbiology laboratory. The infections occurred in children aged 2-3 years, each of whom attended a different child day care center in Lexington-Fayette County (population: 200,000). This report summarizes the findings of an investigation by the LFCHD and the Kentucky Department for Health Services to assess the impact of day care center attendance on communitywide shigellosis.

Public health field nurses obtained stool cultures from family members and day care center contacts of the three children; five contacts tested positive for S. sonnei infection. Despite health education efforts and follow-up by LFCHD, cases continued to occur throughout the community. From January 1 through July 15, 1991, 186 culture-confirmed S. sonnei infections were reported in Lexington-Fayette County.

Investigators attempted to interview an adult member of each family with at least one case of culture-confirmed infection. Questions were asked about the occurrence of diarrhea and child day care center attendance for all household members during January 1 through July 15, 1991. A care of shigellosis was defined as diarrhea (i.e., two or more loose stools per day for 2 or more days) in a person who resided in a household with a person who had culture-confirmed shigellosis. An initial case of shigellosis was defined as the first incidence of diarrhea in a household member.

Of the 186 persons with culture-confirmed infection, 165 (89%) were contacted; these 165 persons represented 109 households, within which 111 initial cases of shigellosis were identified. Of the 64 children aged <6 years with initial cases, 57 (89%) attended licensed day care centers, compared with 44 (67%) of the 66 children who were not initial case-patients (odds ratio = 4.1; 95% confidence interval = 1.5-11.6).

In 1990, approximately 20,000 children aged <6 years lived in Lexington-Fayette County; the total capacity of licensed day care centers in the county was 7754 children (Urban Research Institute, University of Louisville, Kentucky, unpublished data, 1992). Among children aged <6 years, the rates of initial cases were 7.4 per 1000 children who attended licensed child day care centers and 0.6 per 1000 children of the same age group who did not attend day care centers. The rate of initial cases of shigellosis attributable to child day care center attendance was 6.8 per 1000 children aged <6 years, and the attributable risk percentage(*) was 91%. Thus, 52 (91%) of the 57 initial cases among children aged <6 years in licensed child day care and 47% of the 111 initial cases of all ages were attributed to child day care center attendance.

To control shigellosis, in June 1991, LFCHD created a Shigella task force that instituted a diarrhea clinic to facilitate proper diagnosis and treatment, intensified infection-control training and surveillance for shigellosis, and encouraged community-based participation in prevention efforts. Children were monitored in handwashing at day care centers, elementary schools, summer camps, and free-lunch sites. Three weeks after intensive interventions were initiated, the incidence of culture-confirmed cases declined substantially.

Reported by: M Kolanz, J Sandifer, J Poundstone, MD, Shigella Task Force, Lexington-Fayette County; M Stapleton, MSPH, R Finger, MD, State Epidemiologist, Dept for Health Svcs, Kentucky Cabinet for Human Resources. Meningitis and Special Pathogens Br, and Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note: Shigellosis is transmitted by the fecal-oral route; transmission is efficient because the infective dose is low. Minor hygienic indiscretions allow fecal-oral spread from person to person, and many persons with mild illness are in contact with others. As a result, community outbreaks are difficult to control [1].

During 1970-1988, the proportion of young children cared for in licensed centers in the United States increased from 3.5% to 22.0% [2,3]. Child day care center attendance increases the risk for diarrheal disease [4]. The risk for shigellosis is greatest for children aged <6 years [5,6] who are most likely to spread disease to their household members [6]. Behavior typical in toddlers, including oral exploration of the environment and suboptimal toileting hygiene, may be associated with this risk [7].

From 1974 through 1990, 26 cases of Shigella infection in Lexington-Fayette County had been the maximum reported in any year. However, a large outbreak with 112 culture-confirmed cases of shigellosis affected the same community in 1972-73 [5]. In both outbreaks, child day care center attendance was associated with an increased risk for initial cases in households. Secondary attack rates by age group within households were similar in the two outbreaks: for children aged 1-5 years, rates were 47% in 1972-73 and 53% in 1991. However, in 1991, 51% of the initial cases occurred among children aged <6 years who attended a licensed child day care center, compared with 23% in 1972-73. The attributable risk of 91% for day care center attendance among initial cases in young children in 1991 suggests a need for improved infection-control practices in child day care centers.

One of the national health objectives for the year 2000 is to reduce by 25% the number of cases of infectious diarrhea among children who attend licensed day care centers (objective 20.8) [8]. To decrease the likelihood of transmission of diarrheal illness in day care centers, facility operators should ensure the following:

* Staff and children should be instructed in rigorous and consistent handwashing

practices, including the use of soap and running water.

* Staff and children should wash their hands after using the toilet and changing

diapers, and before handling, preparing, serving, and eating food. During an

outbreak of diarrheal illness, staff and children should also wash their hands on

entry to the day care center.

* If possible, staff who prepare food (including bottles) should not change diapers

or assist children in using the toilet. If they perform both functions, they should

practice rigorous handwashing before handling food and after using the toilet,

changing diapers, and assisting children with toilet use.

* Surfaces, hard-surface toys, and other fomites should be decontaminated

regularly; in the setting of a diarrheal outbreak, this should be done at least once

per day.

* Children with diarrhea should be excluded from child day care until they are

well.

* In the outbreak setting, where feasible, convalescing children should be placed

in a separate room with separate staff and a separate bathroom until they have

two stool cultures that are negative for Shigella 48 hours or more after

completion of a 5-day course of antibiotics [9]. If cohorting is not feasible,

temporary closure of day care centers may be considered to interrupt disease

transmission; however, this policy could increase the likelihood of transmission

if children are transferred to other centers [10]. (*)Incidence among children exposed to day care minus incidence among children not exposed to day care, divided by incidence among children exposed to day care.

References

[1]CDC. Community outbreaks of shigellosis-United States. MMWR 1990;39:509-13,519. [2]Keyserling MD. Windows on day care. New York: National Council of Jewish Women, 1972:1-3. [3]Dawson DA. Child care arrangements: health of our nation's children-United States, 1988. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1990. (Advance data no. 187). [4]Bartlett AV, Moore MD, Gary GW, Starko KM, Erben JJ, Meredith BA. Diarrheal illness among infants and toddlers in child day care centers. J Pediatr 1985;107:495-502. [5]Weissman JB, Schmerler A, Weiler P, Filice G, Godby N, Hansen I. The role of preschool children and day-care centers in the spread of shigellosis in urban communities. J Pediatr 1974;84:797-802. [6]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. [7]Pickering LK. The day care center diarrhea dilemma [Editorial]. Am J Public Health 1986;76:623-4. [8]Public Health Service. Healthy people 2000: national health promotion and disease prevention objective--full report, with commentary. Washington, DC: Us Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50212. [9]Tauxe RV, Johnson K, Boase J, Helgerson SD, Blake PA. Control of day care shigellosis: a trial of convalescent day care in isolation. Am J Public Health 1986;76:627-30. [10]Tackett CO, Cohen ML. Shigellosis in day care centers: use of plasmid analysis to assess control measures. Pediatr Infect Dis 1983;2:127-9.

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