Malaria morbidity in high and seasonal malaria transmission area of Burkina Faso

Abstract

Background: Malariometric parameters are often primary endpoints of efficacy trials of malaria vaccine candidates. This study aims to describe the epidemiology of malaria prior to the conduct of a series of drug and vaccine trials in a rural area of Burkina Faso.

Methods: Malaria incidence was prospectively evaluated over one year follow-up among two cohorts of children aged 0-5 years living in the Saponé health district. The parents of 1089 children comprising a passive case detection cohort were encouraged to seek care from the local health clinic at any time their child felt sick. Among this cohort, 555 children were randomly selected for inclusion in an active surveillance sub-cohort evaluated for clinical malaria during twice weekly home visits. Malaria prevalence was evaluated by cross-sectional survey during the low and high transmission seasons.

Results: Number of episodes per child ranged from 0 to 6 per year. Cumulative incidence was 67.4% in the passive and 86.2% in the active cohort and was highest among children 0-1 years. Clinical malaria prevalence was 9.8% in the low and 13.0% in the high season (p>0.05). Median days to first malaria episode ranged from 187 (95% CI 180-193) among children 0-1 years to 228 (95% CI 212, 242) among children 4-5 years. The alternative parasite thresholds for the malaria case definition that achieved optimal sensitivity and specificity (70-80%) were 3150 parasites/µl in the high and 1350 parasites/µl in the low season.

Conclusion: Clinical malaria burden was highest among the youngest age group children, who may represent the most appropriate target population for malaria vaccine candidate development. The pyrogenic threshold of parasitaemia varied markedly by season, suggesting a value for alternative parasitaemia levels in the malaria case defintion. Regional epidemiology of malaria described, Sapone area field centers are positioned for future conduct of malaria vaccine trials.

Figure 1. Age-specific malaria incidence according to the season.

a. Seasonal variation in age-specific clinical malaria incidence evaluated by active surveillance over one year. b. Seasonal variation in age-specific clinical malaria incidence evaluated by passive surveillance over one year.

Figure 2. Prevalence of parasitemia and geometric mean parasite densities according to the season.

a. Age-specific prevalence of parasitemia and geometric mean parasite densities in the high transmission season. Line indicates parasitemia prevalence. Bars indicate geometric parasite density and 95% confidence interval. b. Age-specific prevalence of parasitemia and geometric mean parasite densities in the low transmission season. Line indicates parasitemia prevalence. Bars indicate geometric parasite density and 95% confidence interval.

Figure 3. Time to first malaria episode among children 0–5 years evaluated by active surveillance from the low through high transmission season.

Figure 4. Malaria case definition using objective and subjective fever according to the season.

a. Sensitivity and specificity of alternative parasite threshold for malaria case definition in the high transmission season using objective (> = 37.5 degrees C) and subjective fever. b. Sensitivity and specificity of alternative parasite threshold for malaria case definition in the low transmission season using objective (> = 37.5 degrees C) and subjective fever.

Figure 5. Malaria case definition using objective fever according to the season.

a. Sensitivity and specificity of alternative parasite threshold for malaria case definition in the high transmission season using objective (> = 37.5 degrees C) fever. b. Sensitivity and specificity of alternative parasite threshold for malaria case definition in the low transmission season using objective (> = 37.5 degrees C) fever.