Plasmodium falciparum infections and number needed to screen among refugees arriving from sub-Saharan Africa.

Abstract

Background: Migrants from malaria-endemic countries, especially sub-Saharan Africa (SSA), may harbour parasites at low density in peripheral blood when relocating to non-endemic countries. This study aimed to estimate the number of subclinical malaria infections in SSA refugees arriving to Sweden, and the number needed to screen (NNS) to identify one case.

Methods: Country-specific age-standardized prevalences of Plasmodium falciparum infections from the Malaria Atlas Project (MAP) were applied to demographic data on SSA refugees who had recently arrived in Sweden, 2015-22. Indirect estimates of the number of asymptomatic P. falciparum infections and NNS in different age groups were stratified by country transmission levels.

Results: In total, 3930 (7%) of the 56 248 asylum applicants or quota refugees arriving from SSA during 2015-22 were estimated to be infected with P. falciparum parasites, including 1789 children and 2141 adults, of which 851 women of reproductive age. The estimated total number of individuals with asymptomatic P. falciparum infections arriving in Sweden per year was 491 (range 356-546), and 80% of infections were in individuals from high and moderate-transmission countries. The NNS was estimated to 2-14 in individuals arriving from countries with high and moderate transmission levels.

Conclusions: Modelled estimates of P. falciparum rates in newly arrived refugees correspond to previously reported screening parasite prevalence in SSA migrant populations. A low number of migrants need to be screened to detect one case in populations arriving from high-moderate transmission areas. These estimates can guide screening strategies and could reduce the burden of malaria in migrants from SSA.