Malaria parasite prevalence in Sub-Saharan African migrants screened in Sweden: a cross-sectional study

Asymptomatic infections with malaria parasites are common in populations in endemic areas. These infections may persist in migrants after arrival in a non-endemic area. Screening to find and clear these infections is generally not implemented in non-endemic countries, despite a potential negative health impact. We performed a study to evaluate the Plasmodium parasite prevalence in migrants living in Sweden.

Adults and children born in Sub-Saharan Africa (SSA) were invited in the study between April 2019 and June 2022 at 10 different sites, mainly as part of the national Migrant Health Assessment Program in Stockholm and Västerås, Sweden. Rapid diagnostic tests (RDT) and real-time PCR were used to detect malaria parasites. Prevalence and test sensitivity were calculated with 95% confidence intervals (CI). Univariate and multivariable logistic regression were used to evaluate associations with PCR positivity.

In total, 789 individuals were screened for Plasmodium spp. of which 71 (9.0%) were positive by PCR and 18 (2.3%) also by RDT. When performed during the national screening program, 10.4% was PCR positive. A high prevalence was detected in migrants with Uganda as the country of last residence, 53/187 (28.3%), and in this group the prevalence was highest in children, 29/81 (35.8%). Among the PCR positive, 47/71 (66.2%) belonged to families with at least one other member testing positive (odds ratio [OR] 43.4 (95% CI 19.0-98.9), and the time lived in Sweden ranged between 6 and 386 days.

A high malaria parasite prevalence was found in migrants from SSA, particularly in children offered screening in Stockholm, Sweden during the study period. Awareness of asymptomatic malaria infection is needed and screening for malaria in migrants arriving from high endemic countries should be considered.

The Swedish Research Council, Stockholm County Council and Centre for Clinical Research, Västmanland, Sweden.