Risk factors for gametocyte carriage in uncomplicated falciparum malaria in children.

The risk factors associated with gametocytaemia at presentation and after treatment with different antimalarial drug regimens were evaluated in 767 children enrolled prospectively in 5 antimalarial drug trials between July 1996 and December 2002 in a hyperendemic area of southwestern Nigeria. The children were assigned to one of 6 treatment groups: chloroquine (CQ) only; pyrimethamine-sulfadoxine (PS) only; amodiaquine (AQ) only; CQ combined with chlorpheniramine (CQCP); or PS combined with CQ (CQPS) or AQ (AQPS). At enrolment, 115 (15%) of 767 children were gametocyte carriers. During follow-up, 15.6% of all patients (i.e. 120 patients) developed patent gametocytaemia, which in 85% (102 patients) had developed by day 7 following treatment. In a multiple regression model, 4 factors were found to be independent risk factors for the presence of gametocytaemia at enrolment: male gender (adjusted odds ratio [AOR] = 0.55, 95% confidence interval [CI] 0.36-0.83, P=0.005), absence of fever (AOR = 1.61, 95% CI 1.05-2.5, P=0.03), duration of illness >3 days (AOR=1.57, 95% CI 1.0-2.4, P=0.047), and asexual parasite densities less than 5000/microl (AOR=0.42, 95% CI 0.24-0.73, P=0.002). The presence of patent gametocytaemia at enrolment (AOR=0.04, 95% CI 0.02-0.07, P<0.001) and recrudescence of asexual parasites within 14 days were associated with the presence of gametocytaemia 7 or 14 days after enrolment (AOR=0.5, 95% CI 0.3-0.8, P=0.007). Delay in the time taken to clear the initial parasitaemia (>2 days) was associated with increased risk of subsequent gametocyte carriage. These findings may have implications for malaria control efforts in sub-Saharan Africa where control of the disease depends almost entirely on chemotherapy.