Diagnosis of Plasmodium falciparum malaria at very low parasitaemias using a commercially available LAMP assay and RDT

Background Malaria is the most common tropical infection in the UK. Current guidelines suggest that testing on 3 consecutive days is required following an initial negative result. This study aimed to see whether newer diagnostics (loop-mediated amplification assay [LAMP]) had sufficient sensitivity to support a change in diagnostic practice. Methods Blood samples from 11 participants who had undergone controlled human malaria infection (CHMI) with Plasmodium falciparum malaria were assessed from day 6 (C+6) for malaria positivity using the Carestart Malaria rapid diagnostic test (RDT) and from C+4 using the Alethia Malaria LAMP assay. Quantitative polymerase chain reaction had been performed twice daily during CHMI follow-up. A retrospective analysis of samples submitted to the Sheffield Teaching Hospitals for malaria testing over a 5-y period was conducted, evaluating the combination of the Carestart RDT alongside blood film analysis, as per UK guidelines. Results In CHMI samples, LAMP was positive for all parasitaemias >1000 parasites/ml, whereas RDTs were less reliable (59% positive for parasitaemias >1000 parasites/ml). The combination of RDT and blood films for clinical samples diagnosed most infections, but only a minority of negative samples had subsequent tests. Conclusions LAMP has higher sensitivity than current UK recommended methods, with a potential to review the requirement for additional days of testing in the majority of patients.