Coverage of new ITN distribution was 98.4% and the maximum ITN use fraction was 69%. The percentage of under five years and pregnant women not using ITNs exceeded that of other adults. Being male, younger, and living farther from the vector breeding site were factors associated with less frequent use of ITNs. Residents in the age range 15 to 24 years were the least users of ITNs. Lack of convenient space to hang the ITN was the prominent reason for not using ITN, despite its availability.
ITN use fraction was calculated based on self-report. It may not be possible to avoid bias with self-report. However, listing the names of household members who slept under ITN the night before the interview was considered to be better than asking a Yes/No question. A similar approach was used in previous studies . The fact that the ITN use fraction did not reach 100% (the maximum was 69%) after mass distribution of ITNs was reassuring in that social-desirability bias did not overwhelm this study.
Distance from the vector breeding site affected use of ITNs. This may support the notion that ITN use is associated with risk perception . This was also indicated by the finding that the number of malaria episodes decreases in the household farther from the vector breeding site [16, 17], which might have compelled residents who lived away from the vector breeding site to perceive lower risk of disease and to use ITNs less frequently.
A recent paper showed that before mass ITN distribution, the risk of falciparum malaria was higher in the age category <15 years compared to 15 to 24 years. However, this risk shifted to the age category 15 to 24 years after mass ITN distribution . This could be explained by the significant differences in frequency of ITN use among different age categories, whereby less frequent use of ITNs was observed in the category 15 to 24 years. Though this less frequent use (in 15 to 24 years category) had existed before mass ITN distribution, the increased frequency of ITN use among the younger age categories (<15 years) after mass ITN distribution could move the risk towards 15 to 24 years category.
Educational status and wealth index did not significantly affect ITN use in this study. Some studies reported similar findings [7, 18, 19], while the others showed significant associations between socio-economic factors and ITN use [11, 12]. The presence of prominent vector breeding site yielding varying risk to the households in the study area was worthy of note since the households located closer to the vector breeding site reported more frequent use of ITNs, implying influence of nuisance mosquitoes and/or risk perception might have outweighed factors such as education and wealth, with regard to sleeping under ITNs.
The first four weeks of observation showed adults using ITNs more than the vulnerable groups: under five years and pregnant women. Similarly, during the remaining 97 weeks of follow up, adults used ITNs more than the younger (<24 years) residents and this was not expected. This might also have resulted in lower incidence rate of falciparum malaria among adults since ITN use at individual level was reported to be protective. Similar speculation could be derived for male study participants, as males used ITNs less frequently and suffered more from falciparum malaria .
The most frequent reason for not using ITNs before mass distribution was having worn-out bed nets, mainly because the ITNs were ragged by rats. This implies the need to integrate rodent control measures with ITN distribution in areas with a similar problem in order to lengthen the usable life of ITNs, considering cost implications in distributing free ITNs more often.
Except those who did not receive new ITNs, no household reported inadequacy of number of ITNs received during mass distribution; however, frequency of ITN use did not reach to the coverage. The maximum ITN use fraction was 69% while coverage was 98.4%. Studies indicated such discrepancies between bed net coverage and use [6–8]. Quantitative data showed individual differences in frequency of bed net use including age, gender and risk perception. Meanwhile, according to the responses to the open-ended question, the most frequent reason for not using bed nets, while at least one was available, was lack of convenient space to hang the bed nets. This was also the case in the review made on reported reasons for not using ITNs . This implies mere calculation of ratio of number of household members to bed nets (while distributing the nets), without considering the housing structure or helping the household to hang the desired number of bed nets, would not bring this prevention and control measure to the intended level of efficiency and effectiveness. Meanwhile, the unusual practice of using bed nets for other purposes, including as curtains for traditional pit latrines (though not frequently reported) should be properly addressed.