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Surveillance for Cholera -- Cochabamba Department, Bolivia, January-June 1992

Following the epidemic spread of cholera in Peru (1), in April 1991, health officials in neighboring Bolivia established a surveillance system to detect the appearance and monitor the spread of cholera in their country. The first confirmed case in Bolivia was reported on August 26, 1991; by December 31, 1991, a total of 206 cases had been reported, and 21,324 probable and confirmed cases were reported during 1992. This report summarizes cholera surveillance in Cochabamba department (1992 population: 1,070,000) in central Bolivia (Figure 1) for January-June 1992; the assessment was one element of the Data for Decision Making (DDM) Project conducted by the Child and Community Health Project, Bolivia's Ministry of Social Security and Public Health (MSSPH), the U.S. Agency for International Development (USAID), and CDC.

In April 1991, the MSSPH established three categories of case definitions for cholera surveillance: 1) suspected -- acute diarrhea in a person living in an area where Vibrio cholerae O1 had not been reported previously (stool cultures were obtained from patients with suspected cases); 2) probable -- diarrhea with dehydration, vomiting, and leg cramps in a person living in an area with reported cholera cases or related epidemiologically to another person with cholera (stool cultures were not recommended for patients with probable cases); and 3) confirmed -- diarrhea in a person with a stool culture positive for V. cholerae O1. A two-page case-report form was designed for tabulating and investigating each case and was distributed to all health units in the country. In July 1992, the two-page cholera surveillance form was replaced by a quarter-page surveillance form that collected data on fewer variables.

Cases reported during January 1-June 30, 1992, were analyzed. During this period, 4087 cholera cases in residents of Cochabamba department were reported to the MSSPH; surveillance forms were submitted for 2962 (72%) and oral reports for 1125 (28%) cases. Data about the 2962 cases reported on the surveillance form were used to evaluate the form and to characterize the epidemiology of cholera in Cochabamba department. Of the forms received, data on patient's age, sex, address, and outcome were available for 97% of reported cases; however, information on signs and symptoms of illness was reported for approximately 63% of cases.

The 2962 reported cases included 2667 classified as probable and 295 classified as confirmed and represented an incidence of 2.8 per 1000 population in Cochabamba department. Of the 2962 persons, 1527 (52%) were male (Table 1); 2539 (86%) were aged greater than or equal to 15 years, and 157 (5%) were aged less than 5 years. A total of 1621 (55%) cases occurred in residents of urban areas and 1341 (45%) in residents of rural areas. Of 2878 patients for whom hospitalization status was known, 2449 (85%) were hospitalized; hospitalization rates were similar in urban (83%) and rural (87%) areas. Forty-three persons died (overall case-fatality rate {CFR}=1.4%). Thirteen deaths occurred among all urban cases (CFR=0.8% for urban areas), and 30 deaths occurred among 1328 reported rural cases (CFR=2.2% for rural areas).

Reported by: G Pereira, MD, Ministry of Social Security and Public Health, La Paz; Child and Community Health Project, La Paz; J Flores, MD, Chief of Epidemiology, R Agudo, Health Unit, Cochabamba; US Agency for International Development, Bolivia. US Agency for International Development, Washington, DC. Pan American Health Organization, Washington, DC. Data for Decision Making Project, International Br, Div of Field Epidemiology, Epidemiology Program Office; Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; Div of Field Svcs, International Health Program Office, CDC.

Editorial Note

Editorial Note: Features of the cholera epidemic in Bolivia have been similar to those in neighboring countries: the disease has predominantly affected adults in both rural and urban areas (1). The overall CFR for cholera in Latin America has been approximately 1% (2) -- lower than that in other epidemics (3). The CFR has been higher in rural areas of Latin America (as demonstrated in Cochabamba department), reflecting factors such as lack of access to health care, inadequate distribution of oral rehydration salts, and delays in providing prevention and treatment education outside urban areas (4).

The challenges associated with cholera surveillance in Bolivia are similar to those in other Latin American countries that initiated cholera prevention and control programs after the epidemic began in Peru. For example, surveillance systems established to detect and investigate the earliest cases initially were effective; however, as the number of cases increased, available resources for reporting were strained because 1) complex case definitions constrained reporting and interpretation of data; 2) lengthy and detailed surveillance forms that were useful in investigating the earliest cases were subsequently unnecessary and cumbersome (in Cochabamba department, reporting using the two-page form was considered incomplete, inefficient, and was often delayed for cases in rural areas; essential data elements could be listed on the quarter-page form, and since its introduction, all cholera cases reported to the MSSPH have been reported with the form); and 3) laboratories in areas of intense cholera activity were inundated by requests for cultures to confirm suspect cases. CDC and the Pan American Health Organization have recommended measures to simplify cholera surveillance and facilitate rapid dissemination of surveillance information for Latin America and the Caribbean (see box) (5).

Analysis of surveillance information at levels below the national level provides health authorities with more immediate information on local disease activity, allowing appropriate decisions to be made regarding the distribution of treatment supplies and/or support personnel. The evaluation of cholera surveillance in Cochabamba department for January-June 1992 is a component of the DDM Project in Bolivia. The USAID-funded DDM Project, in which Bolivia is one of five countries collaborating with CDC, aims to increase data-based decision making in public health for formulating health policies and for program planning, monitoring, and evaluation. In 1992, the MSSPH requested assistance from USAID/Bolivia and CDC to provide training to 41 national, regional, and district program managers, epidemiologists, and other health officials in applied epidemiology, management, biostatistics, and communication skills. The evaluation of cholera surveillance in Cochabamba department was one of the 41 applied epidemiology projects conducted as part of this training program. The results of the evaluation described in this report have been used to strengthen cholera surveillance efforts and prevention activities in Bolivia.

References

  1. Pan American Health Organization. Cholera situation in the Americas: an update. Epidemiol Bull 1991;12:11.

  2. CDC. Update: cholera -- Western Hemisphere, 1992. MMWR 1993;42:89-

  3. Glass RI, Black RE. The epidemiology of cholera. In: Barua D, Greenbough WB III, eds. Cholera. New York: Plenum, 1992.

  4. Quick RE, Vargas R, Moreno D, et al. Epidemic cholera in the Amazon: the challenge of preventing death. Am J Trop Med Hyg 1993;48:597-602.



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