The Participation of Secondary Clinical Episodes in the Epidemiology of Vivax Malaria during Pre- and Post-Implementation of Focal Control in the State of Oaxaca, Mexico

The participation of vivax malaria secondary clinical was researched in a retrospective cohort of 33,414 confirmed cases occurring between 1994 and 2005 in the state of Oaxaca, Mexico. Secondary episodes occurred in 23.4% of all primary cases. An increase in secondary episodes was associated with primary cases occurring during the dry sea- sons (risk ratio (RR) = 1.68, 95% CI: 1.45-1.96 ). The incidence of secondary episodes peaked at an older age, occurred similarly in men and women mostly during low mosquito abundance, and had a uniform distribution among localities. A reduction in secondary episodes was associated with the administration of an increased dose and early administration of primaquine (RR = 0.32, 95% CI: 0.26-0.38). However, limitations to distinguish relapses from re-infections impede assessment of the new treatment effect on relapses and its contribution to malaria control in the area . These findings highlight the need for new therapeutic schemes to radical cure of P. vivax infections and operational research aimed at parasite pool elimination .