Factors associated with malaria infection in Honde valley, Mutasa district, Zimbabwe, 2014: a case control study

In January of 2014, an outbreak of malaria was declared in the Honde Valley region of Mutasa District in Zimbabwe. The area has a hot, temperate climate and high rainfall pattern ideal for vector breeding and malaria transmission. Gravity fed irrigation channels span the valley creating a number of breeding sites for malaria vectors, mosquitoes. Malaria outbreaks have been a common occurrence in the district over the past few years despite the district meeting set targets for prevention interventions like indoor residual spraying (IRS) with pyrethroids and long lasting insecticidal nets distribution. The objectives of this study were to describe the outbreak by person, place and time, to assess the community's knowledge on malaria transmission, signs and symptoms and treatment and to tease out factors associated with malaria infection in the district.

An unmatched case-control study was carried out. Interviewer guided questionnaires were administered to residents of the valley who met the inclusion criteria in order to tease out possible factors associated with malaria infection. A case was defined as a resident of Honde Valley with a history of malaria symptoms and a confirmed diagnosis from 13 January 2014 to 26 January 2014. A control was a resident of Mutasa District who was present in the district during the time of the outbreak but did not develop symptoms of malaria. A total of 87 cases and 87 controls were enrolled.

Cases and controls were comparable in terms of socio-demographic characteristics and knowledge on malaria transmission, treatment and prevention. Risk factors associated with contracting malaria during the outbreak were being under the age of 5 years (OR = 9.92, CI 1, 2-80, 1), not using mosquito repellents (OR = 8, 25 CI 3, 78-18, 0), having outdoor activities before dawn and after dusk (OR = 2, 81 CI 1,04-7, 6). Having received indoor residual spraying in ones house was a risk factor for contracting malaria (OR = 1, 68 CI 0, 74-3, 83). This finding was not statistically significant. Sleeping under an insecticidal net and wearing protective clothing when outdoors after dusk were protective factors against contracting malaria (OR = 0, 27 CI 0, 12-0, 59 and OR = 0, 12 CI 0, 06-0, 25 respectively). All cases were treated according to the national malaria case management guidelines.

Risk factors for contracting malaria were being under the age of 5 years, outdoor activities at night and not using mosquito repellents. Net use was a protective factor from contracting malaria in Mutasa District. Indoor residual spraying with pyrethroids in Honde Valley was not a protective factor against contracting malaria.