Determinants of infection
Nearly all malaria infections in the Uganda sites were due to Plasmodium falciparum
. In Ethiopia, P. vivax
was most common, followed by P. falciparum
. The highest malaria prevalence rates were recorded in Butemba in Uganda. Both Ethiopia sites had very low prevalence rates. Overall, the average prevalence rates were 7.0%, 21.1%, 1.0% and 0.5%, in Aduku, Butemba, Hembecho and Guba sites, respectively. Malaria prevalence declined steadily in the Ethiopia sites. In Uganda, prevalence increased significantly in both sites in 2013. In 2014, prevalence decreased significantly in Aduku, but remained high in Butemba.
The number of malaria cases varied considerably among age groups in the Ugandan sites. This variation was most pronounced in Butemba, with infection confined mainly to children under the age of 15, indicating high transmission intensity. The peak malaria prevalence was observed in children from five to nine years old. In Ethiopia, prevalence was low and no differences were observed among the age groups.
In Butemba, a significantly higher malaria prevalence rate was observed in individuals from houses with open or partially open eaves (where the roof meets the wall) compared to individuals from houses with closed eaves. Malaria prevalence varied between groups with varying socio-economic statuses in both Uganda sites, where individuals in households with higher levels had lower infection risks. Use of insecticide treated nets (ITNs) was associated with significantly lower infection in Uganda. In the Ethiopia sites, the difference was not significant, possibly due to the already-low prevalence of malaria.
Regression models were used to evaluate how various factors contributed to malaria prevalence, including age, sex, use of an ITN the previous night, socio-economic status, living in a house with closed eaves, and living in an insecticide-sprayed house. Net use, age and socio-economic status were significant determinants of infection in both study sites in Uganda. Living in a house with closed eaves provided significant protection in Butemba. A person’s sex was a significant factor in Aduku and borderline significant in Butemba.
Individuals who slept under an ITN were less likely to catch malaria, by 37.4% (p=0.011) and 25.8% (p=0.024) in Aduku and Butemba, respectively. Females had a 31.9% (p=0.023) and 19.2% (p=0.062) lower risk of infection compared to males in the two sites. For individuals from households with socio-economic status levels 3-5, the risk was 44.3% and 31.9% lower compared with those from lower status households. In Butemba, the only site with no indoor residual spraying (IRS) programme, individuals who lived in a house with closed eaves had a 31.3% lower risk than those who lived in partially or fully open eaves. This effect was not observed in Aduku, which was under an IRS programme.