Abstract:
Background: The identification of epidemiological pattern of infection with Plasmodium falciparum and Plasmodium
vivax in malaria-endemic area, where multiple episodes are common, is important for intervention programmes.
Methods: A longitudinal cohort study based on weekly house-to-house visits was conducted between July 2008
and June 2010 in 2040 children less than 10 years of age, living nearby the Gilgel-Gibe hydroelectric power dam reser‑
voir in order to determine factors associated with increased P. vivax and P. falciparum incidence. Two types of multivari‑
ate frailty models were applied (using time-to-first malaria episode data and time-to-recurrent malaria episode data),
allowing the estimation of adjusted hazard ratios (AHR) of potential risk factors (gender, age, proximity to the dam
reservoir, and season) for species-specific malaria incidence.
Results: Of 2040 children in 96 weeks of follow up, 864 children experienced at least one malaria episode: 685 due
to P. falciparum in 548 children, and 385 due to P. vivax in 316 children. Plasmodium vivax and P. falciparum malaria
incidence rates were 8.2 (95 % CI: 7.3–9.1) and 14.6 (95 % CI: 13.4–15.6) per 1000 children per month, respectively.
According to the time-to-recurrent event models, children aged ≥7 years had a lower risk of presenting P. vivax
episodes (AHR = 0.6; 95 % CI: 0.4–0.9), but a higher risk of P. falciparum episodes, when compared with children under
≤3 years (AHR = 1.2; 95 % CI: 1.1–1.6). In addition, P. vivax (AHR = 2.7; 95 % CI: 2.2–3.5) and P. falciparum (AHR = 16.9;
95 % CI: 14.3–20.2) episodes were respectively 2.7 and 16.9 times more frequent in the dry season than in the long
rainy season.
Conclusions: The analysis of all malaria episodes (first and recurrent episodes) in the malaria cohort suggests differ‑
ent species-specific patterns of malaria disease in children, with mild seasonality in the incidence of P. vivax episodes
mostly observed in younger age groups, and with marked seasonality in the incidence of P. falciparum episodes
mainly seen in older children.
