Evaluation of the combination of Rapid Diagnostic Tests and microscopy for imported malaria surveillance in Anhui province, China

Background: In the Anhui province, China, efforts to halt local malaria transmission were successful, with no endemic cases reported since 2014. Contrastingly, imported malaria cases are still being reported, indicating a disease reintroduction risk after years of eradication. To avoid this reintroduction, rapid diagnostic tests (RDTs) were combined with microscopy methods to strengthen malaria surveillance. Herein, we aimed to evaluate the efficacy of this surveillance strategy in a field setting. Methods We conducted a retrospective study using malaria surveillance data from January 2016 to June 2020. Epidemiological characteristics and diagnostic information were analysed using descriptive and comparative statistics. The diagnostic performance of the combined toolbox (RDTs plus microscopy) was evaluated based on its sensitivity, specificity, positive and negative predictive values, and Cohen’s kappa coefficient. Results The combined toolbox displayed a higher overall sensitivity for malaria cases than that of microscopy alone (93.74% vs 89.37%; χ 2  = 6.09; p  = 0.14). In contrast to its high sensitivity, the combined toolbox had a specificity of 69.66%. The species identification rates of the combined toolbox for P. falciparum , P. vivax , P. ovale , and P. malariae were 83.15%, 65.00%, 42.11%, and 40.00%, respectively. Conclusions The combination of microscopy and RDTs is an effective strategy for malaria surveillance, possibly detecting more P. falciparum infections than microscopy alone. However, the specificity and ability to identify species of the combined toolbox were not optimal. Thus, monitoring malaria cases in non-endemic areas may require employing more than one diagnostic tool in surveillance strategies. Moreover, further understanding of the advantages and disadvantages of different detection methods is necessary for applying optimum combinations in the field setting.