Is 1+1<2? Exploring Disinhibition Theory and Malaria Prevention Interventions in Angola

In the areas of greatest malaria endemicity and instability, standard protocol consists in large part of simultaneously deploying two interventions: (1) periodic indoor residual spraying (IRS); and (2) insecticide-treated bednets (ITNs), under which people must sleep every night for maximal benefit. This study investigated whether IRS, a relatively convenient procedure, is negatively associated with compliance with the more onerous recommendation of ITN usage, which could indicate that IRS is disinhibiting adherence to ITNs. Participants (N= 9,347) were those who reported living in a household with at least one ITN in the 2011 Angola Malaria Indicator Survey. Logistic regression was used to determine whether having sprayed walls was negatively associated with ITN use after adjusting for individual, household, and environmental characteristics and whether this association was modified by malaria knowledge. Overall, 88% (742) of those with sprayed walls slept under an ITN compared to 76% (6,482) of those without sprayed walls (p<0.0001). Malaria knowledge modified the association between sprayed walls and ITN use (p<0.0001). At the low and moderate knowledge levels, those with sprayed walls had greater odds of using an ITN (aOR=2.36, 95% CI [1.38 4.03] and aOR=1.70, 95% CI [1.14, 2.54]). However, at the high-knowledge level, individuals with sprayed walls had 30% lower odds of sleeping under an ITN than those without sprayed walls (aOR=0.69, 95% CI [0.45, 0.98]). There seems to be a negative, dose-response relationship between knowledge of malaria and use of ITNs when walls are sprayed: vulnerability to disinhibition may grow with increasing knowledge of malaria.