ABSTRACT
OBJECTIVES: This study aimed to estimate the relapse risk of Plasmodium vivax under national chemotherapy scheme using a novel method, and assessed its pattern in Kahnooj, a malaria endemic area in Iran. METHODS: The authors traced repeated episodes of malaria attack between 1994 and 2001 and then, estimated the risks of secondary attack of P. vivax, classified by the species in their primary attack. It is suggested that the difference between the secondary attack rate in those who were infected by P falciparum and P. vivax in their primary attack may estimate the P. vivax relapse rate indirectly. RESULTS: This method showed that the relapse risk of P. vivax with in one and two years after the primary attack were 16.8 and 24.5% respectively. The risks of relapse before three or after 18 months were very low. INTERPRETATION & CONCLUSION: The relapse pattern of P. vivax was compatible with the dominant pattern in most of the temperate areas. In addition, the relapse risk was very close to the estimated relapse risks in clinical trials on anti-relapse drugs. Therefore, we concluded that the anti-relapse therapy in the study area was effective; also, this method may estimate the relapse risk of P. vivax accurately.