Usefulness of PCR for diagnosis of imported malaria in Poland.

The aim of the present study was to use the polymerase chain reaction (PCR) to detect and identify Plasmodium spp. in diagnostic specimens, especially in those from patients diagnosed by microscopy as having possible mixed infections, and in those demonstrating low parasitemia or those that were parasite-negative. For most of the specimens, the PCR results were in accordance with microscopic findings, and in 16.2% of the cases with low parasitemia PCR enhanced the results by identifying the parasite species. This method detected one additional case of Plasmodium falciparum malaria among the patients with fever of unknown origin. The sensitivity of PCR for detecting Plasmodium DNA was found to correspond to 1.35-0.38 and 0.12 for Plasmodium falciparum and Plasmodium vivax parasites per microliter of blood, respectively. Follow-up examinations demonstrated that most of the patients became negative for Plasmodium DNA from 1 to 4 days after the disappearance of parasitemia, as determined by examination of blood films. In conclusion, PCR performed by the reference laboratory significantly enhanced the microscopic diagnosis of malaria and proved very helpful in cases of low parasitemia and in cases of mixed infection.