Decreased prevalence of anemia in highland areas of low malaria transmission after a 1-year interruption of transmission

Abstract

Background: Malaria control campaigns have reduced malaria transmission to very low levels in many areas of Africa. Yet the extent to which malaria interruption or elimination might decrease the prevalence of anemia in areas of low malaria transmission is unknown.

Methods: Kapsisiywa and Kipsamoite, highland areas of Kenya with low, unstable malaria transmission, experienced a 12-month interruption in malaria transmission from April 2007 to May 2008, following high-level coverage (>70% of households) with indoor residual insecticide spraying in 2007. Hemoglobin levels were tested in 1697 randomly selected asymptomatic residents of Kapsisiywa (n = 910) and Kipsamoite (n = 787) at the beginning of a 12-month period of interrupted transmission (in May 2007) and 14 months later (in July 2008).

Results: From May 2007 to July 2008, only 1 of 1697 study cohort members developed clinical malaria. In this period, the prevalence of anemia decreased in Kapsisiywa in all age groups (from 57.5% to 37.9% in children aged <5 years [P < .001], from 21.7% to 10.5% in children aged 5-14 years [P < .001], and from 22.7% to 16.6% in individuals aged ≥ 15 years [P = .004]). The prevalence of anemia in Kipsamoite also decreased in children aged <5 years (from 47.2% to 31.3%; P = .001) but was unchanged in children aged 5-14 years and in individuals aged ≥15 years. Among children <5 years, anemia prevalence was reduced by 34% in both Kapsisiywa (95% confidence interval [CI], 21%-45%) and Kipsamoite (95% CI, 16%-48%).

Conclusions: Successful malaria elimination or interruption may lead to substantial reductions in anemia prevalence even in areas of very low transmission.

Figure 1.

Monthly malaria incidence, 2003–2008, in the study cohort of individuals from Kapsisiywa (top; n = 910) and Kipsamoite (bottom; n = 787), 2 villages in highland Kenya. Boxes indicate periods of indoor residual spraying campaigns in the areas. Arrows indicate the 2 sample collection time points for hemoglobin evaluation, May 2007 and July 2008.