The value of lamp to rule out imported malaria diagnosis: a retrospective observational study in Milan, Italy

Background: The diagnosis of malaria in returning travellers could be a challenge in non-endemic settings. We aimed to assess the performance of LAMP in comparison with standard conventional diagnostic methods using real-time-polymerase chain reaction (PCR) in case of discordant results. Methods: All travellers returning from malaria-endemic areas who presented to our Emergency Department (ED) from January 2017 to December 2020 with signs and symptoms suggestive for malaria were included. Blood microscopy was the reference diagnostic method applied at our laboratory with LAMP implemented as an additional method to aid in malaria diagnosis. PCR was employed only in case of between test's discordant results. Sensitivity and specificity of microscopy compared to LAMP were calculated with the confidence interval of 95%. Results: Four-hundred and eight patients (55.6% male, median age 42 years) were screened for malaria. The diagnosis was confirmed in 49 cases (12%): 44 cases (90%) caused by Plasmodium falciparum. Peripheral blood smear missed to identify three malaria cases, which tested positive with LAMP and PCR. One case of malaria caused by P. malariae in a naive tourist, one case by P. falciparum in a semi-immune pregnant women and one case by P. falciparum in a previously treated semi-immune patient. All the discordant cases were characterized by a very low parasitaemia. Microscopy when compared to LAMP showed a sensitivity of 93.9% (95% confidence interval (CI) 83.1-98.7%) and a specificity of 100% (95% CI 98.9-100%). Conclusions: In our non-endemic setting LAMP was able to identify malaria cases with low-level parasitaemia otherwise missed by blood microscopy.