Cholera Epidemic Associated with Raw Vegetables — Lusaka,Zambia, 2003–2004
Zambia experienced widespread cholera epidemics in 1991 (13,154cases), 1992 (11,659), and 1999 (11,327) (1). In response to thelarge outbreak in 1999, the Zambian Ministry of Health (ZMOH) urgeduse of in-home chlorination with the locally produced solution,Clorin®, and the practice increased substantially Clorin® had beenintroduced in Zambia in 1998 as part of the Safe Water System(SWS), a point-of-use water disinfection and safe-water storagestrategy* launched by the Society for Family Health, in partnershipwith ZMOH, the U.S. Agency for International Development, and CDC.Although no outbreaks were reported during 2000–2002, choleraremained endemic. Epidemic cholera returned to Zambia in November2003, when cases of toxigenic Vibrio cholerae O1, serotype Ogawa,biotype El Tor were confirmed in the capital city, Lusaka. DuringNovember 28, 2003–January 4, 2004, an estimated 2,529 choleracases and 128 cholera deaths (case-fatality rate [CFR] = 5.1%)occurred in Lusaka. In February 2004, the Lusaka District HealthManagement Team (LDHMT) invited CDC to assist in an investigationof the epidemic. This report summarizes the results of thatinvestigation, which implicated foodborne transmission via rawvegetables and demonstrated a protective role for hand washing withsoap. The results underscore the importance of hygiene, cleanwater, and sanitary food handling for cholera prevention.
In response to increasing cases, Zambian authorities beganopening designated cholera-treatment centers (CTCs) in Lusaka inDecember 2003. All seven CTCs were functional by early January2004, and all patients with suspected cholera were referred tothese facilities. During January 5–March 1, an additional 2,101cases and 25 deaths from cholera (CFR = 1.2%) were recorded at CTCsin Lusaka. Investigators conducted a matched case-control study toidentify risk factors for cholera. A case was defined as waterydiarrhea in a person aged >5 years, who was admitted to theChawama (Figure) or Kanyama CTC during February 11–22. Stoolcultures were performed for all eligible patients. Homes ofenrolled patients were visited, and one age-, sex-, andneighborhood-matched control per case was selected systematicallyfrom neighboring households.
A total of 71 case-control pairs were enrolled in the study. V.cholerae O1 was identified in stool cultures from 52 (74%)patients. Both bivariate and multivariate analyses were performed,comparing all cases with culture-confirmed cases; because data werecomparable for the two groups, results are reported for all casesin aggregate. The median age of patients was 27 years (range: 5–75years); 58% were male. Common symptoms, in addition to diarrhea,included vomiting (61 [86%]) and leg cramps (44 [62%]).
Bivariate analysis indicated that consumption of raw vegetableswas associated with cholera (matched odds ratio [MOR] = 3.9; 95%confidence interval [CI] = 1.7–9.6; p = 0.0004). Hand soap wasobserved in 41 (58%) case homes and 64 (90%) control homes.Presence of hand soap was considered a proxy for actual handwashing and was determined to be protective (MOR = 0.14; 95% CI =0.05–0.40; p = 0.0001). Consumption of kapenta, a localsardine-like dietary staple, also was protective (MOR = 0.35; 95%CI = 0.2–0.8; p = 0.005). Drinking untreated water was reported by48 (67%) case-patients and 37 (52%) controls, but the associationwith disease did not reach statistical significance (MOR = 1.9; 95%CI = 0.9–3.9; p = 0.06). In-home chlorination of drinking waterwith Clorin® was reported by 48 (67%) controls and 47 (66%)case-patients. Free chlorine residuals were detected in storedwater in 19 (27%) case homes and 14 (20%) control homes (MOR = 1.5;95% CI = 0.7–3.3; p = 0.21).
Kapenta, raw vegetables, presence of soap, and in-home watertreatment were included in a multivariate model. Water treatment,either by boiling or home chlorination, was not significantlyprotective. Consumption of raw vegetables remained significantlyassociated with cholera (adjusted odds ratio [AOR] = 4.7; 95% CI =1.7–13.0). The presence of hand soap remained significantlyprotective against cholera (AOR = 0.1; 95% CI = 0.04–0.40), as didconsumption of kapenta (AOR = 0.3; 95% CI = 0.1–0.7).
On the basis of these results, the Zambian Central Board ofHealth and LDHMT enhanced cholera-prevention efforts by reinforcinghand-washing promotion messages and recommending that vegetables becooked or washed in treated water. Plans were created to improvehygiene and increase availability of latrines at Lusaka’s majormarket to minimize cross-contamination of produce. Long-termprevention measures under discussion by local authorities includeimproving the quality and quantity of municipal water supplies. InApril, cholera cases declined dramatically, and LDHMT closed theCTCs.
1. What is the purpose of the article?
2. What is the specific case definition?
3. What type of study design was used in thisarticle?
4. How were cases and controls selected.
5. List Several Advantages and Disadvantages (ingeneral) for this type of study design?
6. What are the exposures under investigation?
7. Discuss the epidemiologic triangle for this disease.Agent/host/environment
8. What results were reported in the article? Be sureto report any measures of association and INTERPRET that measure ofassociation (ex. OR). Also include any general conclusions thatwere made in the article. Remember, if a CI includes 1.0, it is notsignificant.
