Molecular diagnosis and species identification of imported malaria in returning travellers in Italy.

A new seminested polymerase chain reaction (sn-PCR)-based protocol was developed and used to detect and identify Plasmodium species in 1226 whole-blood samples from patients (872 Italians and 354 foreigners) with at least 1 symptom compatible with clinical malaria. The results were compared with those obtained by microscopy: 187 samples were positive by microscopy for malaria parasites and 196 were positive by sn-PCR. When compared to microscopy, the sn-PCR detected different malaria parasite species in 11 cases. In 4 of 11 cases, the sn-PCR identified 1 additional malaria parasite species not observed microscopically, suggesting increased sensitivity. In 4 samples with levels of parasitemia too low for accurate identification of species by microscopy, the sn-PCR detected 2 P. falciparum, 1 P. ovale, and 1 P. falciparum plus P. ovale. Moreover, 9 negative samples by microscopy were positive by sn-PCR. Follow-up analysis demonstrated a parasite clearance of P. falciparum DNA up to 3 days after the disappearance of parasitemia at microscopy. In conclusion, sn-PCR-based diagnosis of malaria appears to be a useful tool when the results of conventional techniques are negative in the presence of a syndrome consistent with malaria, yielding accurate species identification and consequential correct treatment.