Comparison of asymptomatic plasmodium spp. infection in two malaria-endemic colombian locations

Background: Asymptomatic infection by Plasmodium spp. could help explain the dynamics of malaria transmission in low-transmission regions. We therefore compared the prevalence of asymptomatic infection by Plasmodium spp. in two Colombian locations, Tierralta and Tumaco, with different transmission patterns, different ecological and epidemiological characteristics and potentially different associated factors. Method: Two cross-sectional studies were carried out between September 2006 and November 2007. Infection by Plasmodium spp. was determined using polymerase chain reaction (PCR) and microscopy. Results:Prevalence of asymptomatic infection at day 0 in Tierralta was 11.3% (95% CI 7.2-16.8) by microscopy and 16.5% (95% CI 11.5-22.9) by PCR, while in Tumaco, values were 2.4% (95% CI 0.7-5.5) and 5.8% (95%CI 2.3-9.2) respectively. General prevalence of asymptomatic plasmodium infection after 28 days of follow-up was 5% (95% CI 3.2-7.7), 6.6% (95% CI 3.8-10.6%) in Tierralta and 3.4% (95% CI 1.5-6.6%) in Tumaco. Plasmodium vivax was predominant in Tierralta, P. falciparum in Tumaco. The main associated factors were male sex (aOR 2.5; 95% CI 1.0-6.7) and two to five previous malaria episodes (aOR 3.0; 95% CI 1.0-9.4). PCR detected 61% more infections than microscopy. Conclusion: Measurement of the prevalence of asymptomatic Plasmodium spp. infection is suggested as part of the epidemiologic evaluation of malaria in low-transmission areas such as Colombia.