Identification of cryptic coinfection with Plasmodium falciparum in patients presenting with vivax malaria

In Thailand, similar to8% of patients treated for vivax malaria are found s ubsequently to have coinfection with Plasmodium falciparum. A P. falciparum histidine rich protein 2 (PfHRP-2) dipstick test was evaluated as a predic tor of mixed infections with subpatent P. falciparum in a prospective study of 238 patients admitted to the hospital with acute vivax malaria. Of thes e, 23 (10%) had subsequent development of falciparum malaria without reexpo sure. Patients with cryptic P. falciparum infection had a significantly low er mean (standard deviation) hematocrit than those with P. vivax alone: 29. 6 (7.6%) versus 37.2 (6.4%) (P < 0.0001). Using microscopic appearance of P . falciparum after the start of treatment as the reference standard, the Pf HRP-2 test was 74% sensitive and 99% specific in predicting mixed infection s with subpatent P. falciparum parasitemia at presentation. The PfHRP-2 dip stick test may be a useful adjunct to microscopy in areas where mixed infec tions are common.