Cholera outbreak associated with drinking contaminated lake shore water, Namayingo District, Uganda, July-August 2023

Cholera is endemic in Uganda with periodic outbreaks occurring annually. On July 24, 2023, Uganda's Ministry of Health confirmed a cholera outbreak in Sigulu Island, Namayingo District. We investigated to determine its magnitude, identify possible exposures, and recommend evidence-based control interventions.

We defined a suspected case as acute onset of watery diarrhea in a resident of Sigulu or Bukana Sub-counties in Namayingo District from July 1-August 15, 2023, and a confirmed case as a suspected case with positive Vibrio cholerae serotype 01 and 0139 stool culture. Cases were identified by active case search and records review at the health centers. We conducted descriptive epidemiology, and environmental assessment at the lakeshore water collection points, and generated hypotheses. In addition, we collected water samples for cholera testing from Jerricans used for domestic water storage and lakeshore water collection points. We conducted an unmatched individual case-control study to compare exposures among case patients and asymptomatic controls residing in Sigulu and Bukana sub-counties.

We identified 24 cases of which 4 were confirmed to have V.cholerae serotype 01 and 0139 ogawa. Fifteen (62%) cases were female and the median age of cases was 27 years (range:2-68 years). Nine (37%) had received the oral cholera vaccine (OCV) 2 to 3 years ago. The epidemic curve showed a point source outbreak after the contamination of a communal water collection point on July 8, 2023, by the primary case who had recently traveled back from a neighboring country with a cholera outbreak. Eighteen (75%) were residents of Secho Village in Sigulu sub-county. All case patients drank lake water. Compared to other water collection points, drinking water from water point A in Secho, Sigulu Sub-county increased the odds of getting cholera (aOR = 4.3, 95% CI: 1.3-15). Treatment of drinking water by any means (aOR = 0.085, 95% CI: 0.097-0.74) and receiving OCV (aOR = 0.16, 95% CI: 0.051-0.56) were protective. We observed residents directly drawing lakeshore water for laundry, bathing, and drinking.

This cholera outbreak in an island community was associated with a traveler's introduction of Vibrio cholerae, followed by community consumption of untreated lakeshore water. Mass distribution of water treatment tablets, repeated OCV, and community mass sensitization about risks associated with drinking untreated lake water helped stop the outbreak.