Cholera Outbreak in Chienge District, Luapula Province, Zambia- 31st May – 9th June 2023: Re-emerging threat

Abstract

Background

Cholera remains a public health threat in Zambia, particularly in hotspot areas like Chienge district in Luapula Province, where the most recent previous outbreak was recorded in 2017. An outbreak of cholera in Chienge was first suspected on May 02, 2023, and confirmed on May 08, 2023. By May 18, 2023, the district had recorded 47 cases. This study aimed to describe cases, identify the cause, and risk factors, and propose control measures.

Methods

An outbreak investigation followed by a 1: 2 matched case-control study were conducted. Suspected cases were individuals aged ≥2 years in the Lunchinda catchment area, presenting with acute watery diarrhoea with or without vomiting or signs of dehydration from April 28 to June 09, 2023. Confirmed cases involved isolation of vibrio cholerae O1 or 0139 from stool samples through culture. Cases and controls were matched by age and sex, with controls from the same household or neighbourhood. A structured questionnaire was used for interviews. The district is situated along the Luapula River and Lake Mweru, and has a total population of 189,893 that mainly depends on fishing as their main source of living. We conducted a descriptive analysis, calculated the case fatality rate (CFR), and applied Conditional logistic regression to determine odds ratios (OR) with 95% confidence interval in R.

Results

Between April 2018 to June 09, 2023, a total of 79 cases were recorded, with 24 lab-confirmed 01 (23 Inaba, 1 Ogawa) species and one community death (CFR: 1.27%). The overall attack rate was 3 cases per 1,000 population. Approximately 80% of the case patients clustered along the lake. All the cases were detected in the health facilities, and 92% exhibited severe dehydration. From 67 cases and 134 controls, none were vaccinated against cholera. The main water source was the lake (41%). The absence of hand washing stations (OR: 2.3, CI: 1.1-4.9), and chlorine before the outbreak (OR: 6.3, CI: 1.3-30.8) were significantly associated with cholera.

Discussion

The outbreak was linked to Vibrio cholerae O1, Inaba serotype. This community lacks safe water, sanitation, and hygiene (WASH) services as it is not under the administrative jurisdiction of the district. Both sexes were equally susceptible. Although the 1.2% fatality rate indicates effective management, it slightly surpasses WHO's threshold, possibly due to late health-seeking behaviours. Unknown vaccination status highlights gaps in coverage since the district conducted Cholera vaccination in the recent past. Risk factors like water source and treatment practices showed varied significance, emphasizing hand hygiene's crucial role.

Conclusion

The outbreak was primarily caused by Inaba serotype. CFR was slightly above the WHO recommendation. Unavailability of chlorine and hand washing stations were the significant risk factors for the outbreak. We recommended continuous health promotion, particularly on WASH.