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To study the risk factors for Plasmodium vivax gametocyte carriage, the presence or absence of gametocytes was determined in 2,125 patients with P. vivax malaria participating in clinical trials at the Hospital for Tropical Diseases in Bangkok, Thailand. Stepwise logistic regression models were used to determine which variables were significantly related to gametocyte carriage. On admission, 615 patients (29%) had detectable gametocytes (before treatment). After treatment had started, an additional 245 patients (11%) developed patent gametocytemia. The variables retained by multivariate analysis were highest observed temperature (adjusted odds ratio [AOR] per °C increase = 0.82, 95% confidence interval [CI] = 0.710.94, P = 0.006), asexual parasitemia > 9,200/µL (AOR = 2.8, 95% CI = 1.94.2, P < 0.0001), erythrocyte counts (AOR = 0.8/million/µL increase, 95% CI = 0.670.95, P = 0.01), monocyte percentage (AOR = 0.93 per % increase, 95% CI = 0.890.96, P < 0.0001), lymphocyte percentage (AOR = 0.98 per % increase, 95% CI = 0.970.99, P = 0.006), albumin (AOR = 0.67 per 10 g/mL increase, 95% CI = 0.50.9, P = 0.007), and anion gap (AOR = 1.1 per unit increase, 95% CI = 1.021.14, P = 0.009). The possible significance of these observations is discussed.
Received October 29, 2003. Accepted for publication January 8, 2004.
Acknowledgments: We thank the staff of the Hospital for Tropical Diseases for their help.
Financial support: This study was supported by grants from Mahidol University. Mathieu Nacher is supported by a Howard Grant from the Institut Pasteur (Paris, France).
Authors addresses: Mathieu Nacher, Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, 10400, Bangkok, Thailand, Shoklo Malaria Research Unit, Intrakiri Road, PO Box 46, Mae Sot, Tak 63110, Thailand and Unité dEpidémiologie des Maladies Emergentes, Institut Pasteur, 25/28 Rue du Dr. Roux, 75015 Paris, France, E-mail: m_nacher{at}lycos.com. Udomsak Silachamroon, Pratap Singhasivanon, Polrat Wilairatana, Weerapong Phumratanaprapin, and Sornchai Looareesuwan, Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, 10400, Bangkok, Thailand. Arnaud Fontanet, Unité dEpidémiologie des Maladies Emergentes, Institut Pasteur, 25/28 Rue du Dr. Roux, 75015 Paris, France.
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