Burden Of Leptospirosis In Cambodia: Preliminary Results Of An Incidence Study

Background: Leptospirosis is an emerging global public health problem in developing countries, especially in the Asia/Pacific Region with an annual incidence estimated at 10-100 per 100,000 pop. Clinical presentation ranges from asymptomatic infection (9-37% in the literature) undifferentiated fever to influenza-like symptoms with or without jaundice or hemorrhage. A small proportion develops various complications which include one or multiple organ failures, with a case-fatality ratio estimated at 40% or more. What is the estimated incidence in Cambodia? Methods: We conducted anonymous, unlinked testing for IgM antibodies to Leptospira spp (PanBio Leptospira IgM ELISA kit) on paired sera of Cambodian patients. These patients were part of a cohort of villagers <20 years of age followed from 2007 - 2009 by active, community-based surveillance for febrile illnesses in a convenience sample of 32 rural villages in four districts of Kampong Cham province, Cambodia. To maximize chances of leptospira positivity, tested samples were those negative for dengue, JEV, influenza A and B, RSV and HMPV as the fevers observed were considered to be due to those infections in samples positive for those viruses. The serostudy bore on a randomly selected subset of 2359 (33%) among 7162 subjects negative for the abovementioned viruses. Results: A total of 99 (4.20%) returned positive for IgM while they were seronegative on an early sample. After extrapolation to the entire study population, the global estimated attack rate for symptomatic infection by pathogenic leptospires among all persons aged <20 years and followed up is estimated at 1.40% [CI95%: 1.26% – 1.55%] for the cumulated study (exposure) periods totaling 28 months. The global incidence for symptomatic IgM seroconversion is estimated at 1.55 p. 1,000 person-month [1.39 – 1.72] (12.9 p. 100,000 person-year), varying from 1.30 [1.08 – 1.57] to 2.04 [1.73 -2.40], depending on the year of the study. Conclusion: Attack rates for symptomatic leptospirosis IgM seroconversion are high in rural Cambodia, even in the absence of identified epidemics. These preliminary and global results are being complemented by microscopic agglutination test (MAT), in-depth biostatistical analyses of individual risk factors and geolocalization of leptospira hotspots in the study area.