Malaria Outbreak Propagated by Rain Water Harvesting and Increased Vector Breeding Sites, Butambala District, Uganda, August 2018-February 2019

Summary

In early February 2019, the Butambala District Health Office reported an upsurge of malaria cases through the National Malaria Control Pro-gram (NMCP). Preliminary analysis of District Health Information System (DHIS2) malaria data showed that the cases exceeded the action threshold from Epidemic week 1 to 6 of 2019. The most affected sub-counties were Kibibi and Budde. We investigated to assess the out-break’s magnitude, identify transmission risk factors, and recommend evidence-based control measures. We defined a confirmed case as malaria positive by rapid diagnostic test (mRDT) or microscopy from 1 August 2018 to 25 February 2019 in a resident or visitor of Kibibi and Budde sub-counties, Butambala District, Uganda. A total of 6,718 case-patients were identified (Attack rate (AR) =6.6%) and no fatalities). Females (AR=7.1%) were slightly more affected than males (AR=6.2%). The most affected age-group was 5-18 years (AR=10%). In the case-control study, 73% (87/120) of case-patients and 62% (74/120) of controls had water harvesting containers (OR_M-H=1.6 ,95% CI=1.0-2.0) two weeks before symptom onset; 80% (96/120) of case-patients and 58% (69/120) of controls carried out late outdoor activities (OR_M-H=3, 95% CI 1.6-5.2) two weeks before symptom onset; 63%(76/120) of case-patients and 71% (85/120) of controls had used Long Lasting Insecticide Nets (LLINS) the previous night (OR_M-H=0.7 95% C.I 0.4-1.2). Environment assessment revealed extensive use of drums and pots to harvest rain water due to lack of piped water and limited boreholes which was favorable for mosquito breeding. In addition, there were stone quarries which led to stagnation of rain water. Entomological assessment of the water in the harvesting containers showed presence of mosquito larvae. Prolonged vector breeding in water harvesting containers and stone quarries was sustained by the intermittent heavy rains; these coupled with inadequate malaria preventive measures caused this outbreak. We recommended frequent draining of the water harvesting containers, increasing coverage for LLINs, and larviciding of vector breeding sites.

Introduction

In Uganda, clinically diagnosed malaria is the leading cause of morbidity and mortality, accounting for 30-50% of outpatient visits at health facilities, 15-20% of all hospital admissions, and up to 20% of all hospital deaths. Twenty seven percent (27%) of inpatient deaths among children under five years of age are due to malaria. Uganda has one of the highest malaria transmission rates in the world and is third in malaria mortality in Africa. Temperature and rainfall are two climatic factors previously used to forecast malaria outbreaks in East Africa. The transmission intensity of malaria depends on vector population or density which also depends on the presence of breeding sites and favorable temperatures; parasite-carrying individuals from whom mosquitoes pick the parasites; and presence of a malaria susceptible populations, especially people with low immunity The influence of climatic factors on malaria infection may differ from place to place based on many local contexts like availability of good public health system for malaria prevention and treatment, socio-economic factors, and local land use. Comprehensive intervention policies and strategies have been adopted to control malaria in Uganda. In early February 2019, the Butambala District Health Office reported an up-surge of malaria cases through the National Malaria Control Program (NMCP). Preliminary analysis of District Health Information System (DHIS2) malaria data showed that the cases exceeded the action thresholds from Epidemic week 1 to 6 of 2019. The most affected sub-counties were Kibibi and Budde. We investigated to assess the out-break’s magnitude, identify transmission risk factors, 7720 and recommend evidence-based control measures.

Methods

We defined a confirmed case as a positive malaria test result by mRDT or microscopy from 1 August 2018 to 25 February 2019 in a resident or visitor of Kibibi and Budde sub-counties, Butambala District, Uganda. We reviewed health records in health facilities of the two most affected sub-counties. We systematically searched for malaria cases by reviewing outpatient health records in health facilities of the two most affected sub-counties. We abstracted data from the registers, including age, sex, village, parish and sub-county of residence, type of confirmatory test done and described cases by person, place, and time. We conducted environmental and entomological assessments in the most affected villages in the two sub-counties. We generated hypotheses and conducted a case control study to compare exposures among cases and controls, frequency matched by age and village with a ratio of 1:1.

Results

We line listed 6,718 confirmed case-patients with median age 13 years (Interquartile Range [IQR]: 7-24 years) and no fatalities. Fe-males (AR=7.1%) were more affected than males (AR=62%). The most affected age-group was 5-18 years (AR=10%). Mabanda parish (AR=41%) in Kibibi sub-county and Kibugga parish (AR=38%) in Budde sub-county, were most affected. The epidemic curve showed a steady increase in malaria cases from August 2018, with peaks in December 2018 and February 2019 following intermittent heavy rainfall.

Environmental assessment and Entomological findings

The most affected villages were characterized with many spots of standing water following heavy rainfall. There was accumulation of rain water in the large pits and stone quarry created by road contractors and these became breeding sites for mosquitoes. Increased human activities around flowing streams such as ginger growing and cultivation led to their blockage hence acted as extra bleeding site for mosquitoes. The pyrethrum spray catch (PSC) yielded Anopheles gambiae.

Case-control findings

In the case-control study, 73% (87/120) of case-patients and 62% (74/120) of controls had water harvesting containers (OR_M-H=1.6 ,95% CI 1.0-2.0) two weeks before symptom onset; 80% (96/120) of case-patients and 58% (69/120) of controls carried out late outdoor activities (OR_M-H=3, 95% CI 1.6-5.2) two weeks before symptom onset ; 63% (76/120) of case-patients and 71% (85/120) of controls had used LLINs previous night (OR_M-H=0.7 95% C.I 0.4-1.2).

Discussion

This investigation revealed that presence of rain water harvesting containers facilitated this outbreak. The two most affected parishes lacked piped or borehole water for the population. During the environment assessment, it was evident that during the rainy season, most people harvested water. The containers used in harvesting water were drums, fixed pots, jerry cans, and saucepans. The rain water harvesting containers permanently stayed out-doors and many al-ways had water residues. During the rainy season of October to December, the rains were prolonged and the containers retained water for longer periods than previously. This led to increased breeding sites for mosquitoes around the homesteads. A study carried out in India shows that water harvesting containers such as over-head tanks were potential breeding habitat for mosquitoes (3).

Our investigation also revealed that males were more affected than males. This could be because women do more activities that expose them to mosquito breeding sites, such as fetching water from various water sources and late night cooking outside the main house. A study carried out in Tanzania found that females were more susceptible to malaria attacks than men because they perform activities that predispose them to mosquito bites. Most activities done by women included late night outdoor cooking, fetching water from the water bodies, cultivation [4].

The environmental assessment revealed that human activities conducted along running streams such as ginger washing and road construction could have propagated this outbreak. In January 2018, the road contractors started mining stones for road construction. How-ever, in October 2018, they suspended the road construction leading to the accumulation of rain water in the stone quarry. This acted as breeding sites for mosquitoes.

Conclusions

Prolonged vector breeding in water harvesting containers sustained by the heavy rains, together with inadequate malaria preventive measures caused facilitated this outbreak. We recommended frequent draining of the water harvesting containers, increased cover-age for LLINs, and larviciding breeding sites.

References

1. MOH (2015) Health Sector Development Plan 20 11 /12 – 2019/20. doi:1093/intimm/dxu005.
2. World Malaria Report 2013 https://www.who.int/malaria/ publications/world_malaria_report_2013/en/
3. Shalu Thomas, Sangamithra Ravishankaran, Johnson A. Justin, Aswin Asokan, Manu T. Mathai, Neena Valecha, Matthew B. Thomas and Alex Eapen. Overhead tank is the potential breeding habitat of Anopheles stephensi in an urban transmission setting of Chennai, India .Malaria Journal201615:274https://doi.org/10.1186/ s12936-016-1321-7
4. Chiruvu RT, Kanengoni B, Mungati M, et al. Malaria Outbreak investigation in Chitulipasi, Beitbridge District, Matabeleland South Province, 2015. IJRDO-Journal of Health Sciences and Nursing. 2017; 2 (5): 104–120