Risk Factors Associated with Malaria Infection Identified through Reactive Case Detection in Zanzibar, 2012-2019

Abstract BackgroundOver the past two decades, Zanzibar substantially reduced malaria burden. As malaria decreases, sustainable improvements in prevention and control interventions may increasingly depend on accurate knowledge of malaria risk factors to further target interventions. This study aimed to investigate the risk factors associated with malaria infection in Zanzibar. MethodsWe analyzed surveillance data from Zanzibar’s Malaria Case Notification system collected between August 2012 and December 2019. This system collects data from all malaria cases passively detected and reported by public and private health facilities, from household-based follow-up and reactive case detection activities linked to those primary cases. All members of households of the passively detected malaria cases were screened for malaria using a malaria rapid diagnostic test (mRDT); individuals with a positive mRDT result were treated with artemisinin-based combination therapy. Univariate and multivariate logistic regression analyses were done to investigate the association between mRDT positivity among the household members and explanatory factors (i.e., age, sex, history of fever, history of travel, rainfall, long-lasting insecticidal net [LLIN] density, LLIN use, household indoor residual spraying [IRS], and household location) with adjustment for seasonality ResultsThe findings show that younger age ( p-value for trend<0.001 ), history of fever in the last two weeks (odds ratio [OR]=32.0; 95% CI: 29.1-35.3), history of travel outside Zanzibar in the last 30 days (OR=2.3; 95% CI: 2.1-2.6) and living in Unguja (OR=1.2; 95% CI: 1.1-1.3) were independently associated with increased odds of mRDT positivity. In contrast, male sex (OR=0.8; 95% CI: 0.7-0.9), having higher household LLIN density ( p-value for trend<0.001 ), sleeping under an LLIN the previous night (OR=0.8; 95% CI: 0.7-0.9), and living in a household that received IRS in the last 12 months (OR=0.9; 95% CI: 0.8-0.9) were independently associated with reduced odds of mRDT positivity. A significant effect modification of combining IRS and LLIN was also noted (OR=0.7; 95% CI:0.6-0.8).ConclusionsThe findings suggest that vector control remains an important malaria prevention intervention: they underscore the need to maintain universal access to LLINs, the persistent promotion of LLIN use, and application of IRS. Additionally, enhanced behavioral change and preventive strategies targeting children aged 5-14 years and travelers are needed.