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To evaluate transmission potential of Plasmodium falciparum, we use the area under the curve (AUC) of gametocyte levels after treatment as an approach to combine their duration and magnitude. Analysis of determinants of AUC was based on two main exposures: parasite clearance time (PCT) and presence of dihydrofolate reductase and dihydropteroate synthase mutations associated with sulfadoxine-pyrimethamine (SP) resistance in vitro. Exposures were determined based on the first three days after treatment with SP of 96 individuals who had malaria, cleared parasitemia by days 13, and were followed-up for 21 days. Using regression methods, we characterized both the heterogeneity of the presence of gametocytes (AUC > 0) and the magnitude of the AUC among those with an AUC > 0. A PCT of two or three days was associated with a substantial and highly significant odds ratio for presence of gametocytes. Among those who developed gametocytes, if their clearance time was 3 days or if they had any mutations (1 or 2) the magnitude of gametocytemia was
3-fold. Methods presented are applicable to both observational studies and clinical trials assessing the effect of therapies on transmission potential.
Received January 25, 2006. Accepted for publication May 31, 2006.
Financial support: This research was supported in part by a grant AI055687-02 from the National Institutes of Health, and the Universidad del Valle, Cali, Colombia.
* Address correspondence to Fabián Méndez, Escuela de Salud Pública, Universidad del Valle, San Fernando, Calle 4B No. 36-140, Edificio 118, Cali, Colombia. E-mail: famendez{at}univalle.edu.co
Authors addresses: Fabián Méndez, Escuela de Salud Pública, Universidad del Valle, San Fernando, Calle 4B No. 36-140, Edificio 118, Cali, Colombia, Fax: 57-2-557-0425, E-mail: famendez{at}univalle.edu.co. Álvaro Muñoz, Department of Epidemiology, The Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, E-7648, Baltimore, MD 21205, E-mail: jvaldez{at}jhsph.edu. Christopher V. Plowe, Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore Street, HSF 480, Baltimore, MD 21201, E-mail: cplowe{at}medicine.umaryland.edu.
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