Abstract:
Introduction: Malaria surveillance is a key pillar in the control of malaria in Africa. The
value of using routinely collected data from health facilities to define malaria risk at
community levels remains poorly defined.
Methods: Four cross-sectional parasite prevalence surveys were undertaken among
residents at 36 enumeration zones in Kilifi county on the Kenyan coast and temporally
and spatially matched to fever surveillance at 6 health facilities serving the same
communities over 12 months. The age-structured functional form of the relationship
between test positivity rate (TPR) and community-based parasite prevalence (PR) was
explored through the development of regression models fitted by alternating the linear,
exponential and polynomial terms for PR. The predictive ranges of TPR were explored for
PR endemicity risk groups of control programmatic value using cut-offs of low (PR <5%)
and high (PR ≥ 30%) transmission intensity.
Results: Among 28,134 febrile patients encountered for malaria diagnostic testing in the
health facilities, 12,143 (43.2%: 95% CI: 42.6%, 43.7%) were positive. The overall
community PR was 9.9% (95% CI: 9.2%, 10.7%) among 6,479 participants tested for
malaria. The polynomial model was the best fitting model for the data that described the
algebraic relationship between TPR and PR. In this setting, a TPR of ≥ 49% in all age
groups corresponded to an age-standardized PR of ≥ 30%, while a TPR of < 40%
corresponded to an age-standardized PR of < 5%.
Conclusion: A non-linear relationship was observed between the relative change in TPR
and changes in the PR, which is likely to have important implications for malaria
surveillance programs, especially at the extremes of transmission. However, larger, more
spatially diverse data series using routinely collected TPR data matched to community based infection prevalence data are required to explore the more practical implications of
using TPR as a replacement for community PR.