|dc.description.abstract||Ambient temperature is an important determinant of malaria transmission and suitability, afecting
the life-cycle of the Plasmodium parasite and Anopheles vector. Early models predicted a thermal malaria transmission
optimum of 31 °C, later revised to 25 °C using experimental data from mosquito and parasite biology. However, the
link between ambient temperature and human malaria incidence remains poorly resolved.
To evaluate the relationship between ambient temperature and malaria risk, 5833 febrile children
(<18 years-old) with an acute, non-localizing febrile illness were enrolled from four heterogenous outpatient clinic
sites in Kenya (Chulaimbo, Kisumu, Msambweni and Ukunda). Thick and thin blood smears were evaluated for the
presence of malaria parasites. Daily temperature estimates were obtained from land logger data, and rainfall from
National Oceanic and Atmospheric Administration (NOAA)’s Africa Rainfall Climatology (ARC) data. Thirty-day mean
temperature and 30-day cumulative rainfall were estimated and each lagged by 30 days, relative to the febrile visit.
A generalized linear mixed model was used to assess relationships between malaria smear positivity and predictors
including temperature, rainfall, age, sex, mosquito exposure and socioeconomic status.
Malaria smear positivity varied between 42–83% across four clinic sites in western and coastal Kenya,
with highest smear positivity in the rural, western site. The temperature ranges were cooler in the western sites and
warmer in the coastal sites. In multivariate analysis controlling for socioeconomic status, age, sex, rainfall and bednet
use, malaria smear positivity peaked near 25 °C at all four sites, as predicted a priori from an ecological model.
This study provides direct feld evidence of a unimodal relationship between ambient temperature
and human malaria incidence with a peak in malaria transmission occurring at lower temperatures than previously
recognized clinically. This nonlinear relationship with an intermediate optimal temperature implies that future climate
warming could expand malaria incidence in cooler, highland regions while decreasing incidence in already warm
regions with average temperatures above 25 °C. These fndings support eforts to further understand the nonlinear
association between ambient temperature and vector-borne diseases to better allocate resources and respond to
disease threats in a future, warmer world.||en_US