Trends and factors associated with confirmed clinical malaria in an urban sentinel surveillance site in Melen, Libreville, Gabon: a 15-year retrospective study (2010–2024)

Malaria remains a major public health problem in sub-Saharan Africa, including Gabon, where urban transmission is increasingly recognised. Despite the strategic importance of sentinel surveillance systems, long-term data describing malaria trends and factors associated with malaria positivity in urban settings remain scarce. We examined how malaria test positivity evolved, and which patient-level and seasonal factors were related to it, over a 15-year period in Libreville. A retrospective analytical study was conducted using passive surveillance data collected at the Melen sentinel site between 2010 and 2024. Febrile patients undergoing malaria testing by microscopy were included. Malaria test positivity rate (TPR) was calculated as the proportion of positive thick blood smears. Demographic, behavioural and seasonal factors were related to positivity through logistic models; estimates are reported as crude and adjusted odds ratios, each with its 95% interval. A total of 33,643 patients were included, with an overall malaria TPR of 35.2%. After an initial increase between 2010 and 2012, TPR declined to a minimum in 2019, followed by a marked resurgence reaching 48.1% in 2024. Age was strongly associated with malaria positivity, with adults aged of more than 15 years exhibiting the highest odds of infection comparatively to children under 5 years and no difference in the malaria transmission between adults and 5–15 years old populations. Insecticide-Treated Net use was associated with lower malaria test positivity, whereas absence of self-medication and longer fever duration were associated with increased odds of infection. Malaria TPR was significantly higher during dry seasons compared to rainy seasons. Malaria transmission remains sustained in urban Libreville, with a clear resurgence in recent years. The observed shift in the age distribution of malaria positivity towards older age groups, and the associations between malaria TPR and behavioural and climatic factors, highlight the need for adaptive, urban-specific and climate-informed control strategies. Not applicable.