Risk factors for gametocyte carriage in uncomplicated falciparum malaria

The factors affecting the development of patent Plasmodium falciparum gamet ocytemia were assessed in 5,682 patients entered prospectively into a serie s of antimalarial drug trials conducted in an area of low and seasonal tran smission on the western border of Thailand. Of the 4,565 patients with admi ssion thick smear assessments, 110 (2.4%) had gametocytemia. During the fol low-up period 170 (3%) of all patients developed patent gametocytemia, whic h in 89% had developed by day 14 following treatment. In a multiple logisti c regression model five factors were found to be independent risk factors a t presentation for the development or persistence of gametocytemia during f ollow up; patent gametocytemia on admission (adjusted odds ratio [AOR] = 7. 8, 95% confidence interval [CI] = 3.7-16, P < 0.001), anemia (hematocrit <3 0%) (AOR = 3.9, 95% CI = 2.3-6.5, P < 0.001),no coincident P. vivax malaria (AOR = 3.5, 95% CI = 1.04-11.5, P < 0.04), presentation with a recrudescen t infection (AOR = 2.3, 95% CI = 1.3-4.1, P < 0.004), and a history of illn ess longer than two days (AOR = 3.3, 95% CI = 1.7-6.6, P < 0.001). Patients whose infections responded slowly to treatment or recrudesced subsequently were also more likely to carry gametocytes than those who responded rapidl y or were cured (relative risks = 1.9, 95% CI = 1.3-2.7 and 2.8, 95% CI = 2 .0-4.0, respectively; P < 0.001). These data provide further evidence of im portant epidemiologic interactions between P. falciparum and P. vivax, and drug resistance and transmission potential.