Hidden reservoirs of infection: prevalence and risk factors of asymptomatic malaria in a high-endemic region of Zambia.

Background: Malaria remains a significant global health challenge, particularly in sub-Saharan Africa (SSA), where asymptomatic cases contribute to ongoing transmission and hinder elimination efforts. Asymptomatic individuals act as hidden reservoirs, sustaining onward malaria transmission. This study aimed to determine the prevalence and risk factors of asymptomatic malaria in Mwandi District, Zambia.

Methods: A cross-sectional study was conducted between January to May 2024 in Mwandi District. Blood samples were collected for malaria diagnosis and simultaneously tested using rapid diagnostic tests and Giemsa-stained blood smear microscopy techniques to detect Plasmodium infections. Structured questionnaires were administered to gather demographic data and information on potential risk factors. Descriptive statistics were used to summarize the data while categorical variables were compared using the chi-square test or Fisher's exact test. Logistic regression was used to assess associations between outcomes and independent variables, with statistical significance set at p < 0.05.

Results: A total of 370 participants were enrolled in the study, with females comprising the majority (52.4%) and a median age of 24 years (IQR: 9-30). The overall prevalence of asymptomatic malaria was (4.1%), as determined by microscopy. Logistic regression analysis showed that females had significantly lower odds of asymptomatic malaria compared to males (AOR: 0.20, 95% CI 0.05-0.68; p = 0.010). Additionally, participants residing in Matoya and Sikute were more likely to have asymptomatic malaria, with adjusted odds ratios of 4.56 (95% CI 1.10-18.80; p = 0.036) and 4.72 (95% CI 1.03-21.50; p = 0.045), respectively. No significant associations were found with insecticide-treated net use, indoor residual spraying, or socioeconomic status.

Conclusion: The findings highlight the need for targeted surveillance and interventions in high-risk groups and locations to curb silent transmission. Despite limitations in diagnostic sensitivity, the study underscores the importance of integrating asymptomatic malaria screening into control programmes to advance elimination efforts in Zambia and similar endemic regions.