BACKGROUND : Indoor residual spraying (IRS) is known to reduce malaria transmission. In northern Uganda, a high
endemic area, IRS has been implemented since 2006. Limited data however, exists on the effect of IRS on the malaria
burden. This study sought to assess the effect of IRS on malaria morbidity in the high intensity area of northern
Uganda. Retrospective routine data from ten health facilities in three districts which had received at least five rounds
of IRS in northern Uganda was analysed. The primary outcome of interest was malaria morbidity, measured by the
slide positivity rate (SPR). Descriptive statistics were used to describe the malaria morbidity stratified by age and sex.
The average change in the malaria morbidity, measured by the SPR was assessed according to time, measured as
calendar months. A fixed-effects linear regression model was used which included a polynomial function of time and
controlled for malaria seasonality and variations between districts/facilities.
RESULTS : The total out-patient department attendance in the ten health facilities for the study period was 2,779,246,
of which 736,034 (26.5%) malaria cases were diagnosed with 374,826 (50.9%) cases of under 5 years and an overall
SPR of 37.5%. The percentage point (p.p.) changes in SPR according to time measured as calendar months following
IRS, revealed a decreasing trend in malaria morbidity in the first 3 months following each round of IRS. The highest
percentage point decrease in the SPR was observed in the second month following IRS (9.5 p.p., CI −17.85 to −1.16,
p = 0.026), among patients above 5 years. The SPR decline however waned by the fourth month following IRS, with
an increase in the SPR of 8.4 p.p. at district level by the sixth month, p = 0.510.
CONCLUSION : The study results show that IRS was associated with a significant reduction in malaria morbidity in
northern Uganda in the first 3 months following IRS. The malaria reduction however waned by the fourth month following