High rate of Plasmodium vivax relapse following treatment of falciparum malaria in Thailand.

Within two months of treatment for falciparum malaria, Plasmodium vivax infections developed in 58 (33%) of 174 patients who had received a quinine or quinidine regimen and in 46 (32%) of 145 patients who had received mefloquine with inpatient follow-up of more than six weeks. The time to vivax relapse was significantly longer after mefloquine treatment (median 47 days, range 30-65) than after quinine or quinidine treatment (21 days, 15-36; p less than 0.0001). All patients remained outside areas of malaria transmission. These findings suggest a very high rate of double infection in Thailand with acute suppression of vivax by falciparum malaria, and warrant evaluation of radical therapy with primaquine in certain patients with acute falciparum malaria.