Insecticide-treated net use before and after mass distribution in a fishing community along Lake Victoria, Kenya: successes and unavoidable pitfalls
© Larson et al.; licensee BioMed Central. 2014
Received: 20 November 2014
Accepted: 21 November 2014
Published: 28 November 2014
Insecticide-treated nets (ITNs) have proven instrumental in the successful reduction of malaria incidence in holoendemic regions during the past decade. As distribution of ITNs throughout sub-Saharan Africa (SSA) is being scaled up, maintaining maximal levels of coverage will be necessary to sustain current gains. The effectiveness of mass distribution of ITNs, requires careful analysis of successes and failures if impacts are to be sustained over the long term.
Mass distribution of ITNs to a rural Kenyan community along Lake Victoria was performed in early 2011. Surveyors collected data on ITN use both before and one year following this distribution. At both times, household representatives were asked to provide a complete accounting of ITNs within the dwelling, the location of each net, and the ages and genders of each person who slept under that net the previous night. Other data on household material possessions, education levels and occupations were recorded. Information on malaria preventative factors such as ceiling nets and indoor residual spraying was noted. Basic information on malaria knowledge and health-seeking behaviours was also collected. Patterns of ITN use before and one year following net distribution were compared using spatial and multi-variable statistical methods. Associations of ITN use with various individual, household, demographic and malaria related factors were tested using logistic regression.
After infancy (<1 year), ITN use sharply declined until the late teenage years then began to rise again, plateauing at 30 years of age. Males were less likely to use ITNs than females. Prior to distribution, socio-economic factors such as parental education and occupation were associated with ITN use. Following distribution, ITN use was similar across social groups. Household factors such as availability of nets and sleeping arrangements still reduced consistent net use, however.
Comprehensive, direct-to-household, mass distribution of ITNs was effective in rapidly scaling up coverage, with use being maintained at a high level at least one year following the intervention. Free distribution of ITNs through direct-to-household distribution method can eliminate important constraints in determining consistent ITN use, thus enhancing the sustainability of effective intervention campaigns.
Insecticide-treated bed nets (ITNs) have proven instrumental in the fight against malaria in sub-Saharan Africa (SSA) [1, 2]. The World Health Organization (WHO) has recommended that all health ministries and donor agencies scale up the distribution of ITNs, specifically to target populations of small children and pregnant women . ITNs have been shown to be associated with an average 20% reduction in overall parasite prevalence across a number of geographic contexts  accompanied by precipitous drops in certain Anopheles vector species in Kenya .
However, despite massive scale-up of ITN distribution all over SSA, shortfalls and inequities exist , which might compromise long-term elimination or control programmes. Possession of ITNs has been shown to be associated with factors such as proximity to distribution sites, cost, socioeconomic status, and the method of distribution [6–10]. ITN distribution programmes can rapidly increase ownership and bolster household use. In Sierra Leone, for example, a mass distribution campaign increased household use 137% within six months . Possession, however, does not necessarily imply proper use. Whether ITNs are effectively used to prevent malaria depends on a complex set of factors. In one Ghana study, people used ITNs to reduce the nuisance of mosquitoes, and not to prevent malaria . In the western Kenyan highlands, another study showed that seasonal patterns of precipitation and vector density, along with education, were associated with ITN use . Sleeping arrangements, such as sleeping on the floor (as opposed to a bed), and availability of areas amenable to hanging nets also have been shown to be associated with ITN use . Comprehensive knowledge of malaria risk factors, and education about the purpose of ITNs has increased use among pregnant women in Nigeria .
Challenges to maintaining consistent coverage and compliance following ITN distribution scale-ups have been presented in various other investigations. One study in Burkina Faso noted declines in motivation less than one year following widespread distribution, citing problems of convenience and the perception that malaria is multi-factorial . Leakage of freely distributed nets (loss or disappearance of ITNs following distribution) was seen in a Senegal study, with nearly 10% of nets provided to the community being absent from target households six months later . Leakage has also been shown to compromise the cost-effectiveness of distribution campaigns . To confront challenges that ensure widespread compliance, research has suggested that providing even minimal education can effectively increase household use compared with other methods [19, 20].
To further evaluate the complex interaction of factors that impact effective ITN scale-up, the current project investigated patterns of ITN use before and one year following a mass distribution campaign. This research explored determinants of use at the individual, household and community level in order to uncover factors that may compromise future, sustained efforts to expand ITN ownership and use.
Between January 2012 and August 2012, field workers revisited all households in the area with the aim of assessing the condition of the nets that were distributed roughly one year prior. Permission was again requested from an available adult household representative and the survey was conducted for those households agreeing to participate. For the post-distribution round of data collection, a comprehensive, standardized, oral survey was created which included demographic questions, educational level achieved, and the occupations of male and female household heads. The survey teams recorded the presence of material goods such as radios, electricity and various types of livestock, and also noted types of roof and wall construction. From this, a composite household material wealth index was created using a principal components analysis (PCA) methodology common to analyses of socioeconomic status or households in developing countries. Membership in community groups such as churches and school attendance of children was recorded. Questions about malaria and ITN knowledge, along with general questions on health-seeking and malaria-related health behaviours were asked.
Survey workers made a complete accounting of all nets in the household. Type and condition of each net, and the age and gender of the person(s) sleeping under each, was recorded. Nets that had been previously given out in the mass distribution were identifiable through a known code written on the brand tag of the ITN, but other nets were also recorded. Field workers also documented whether or not dwellings had closed or open eaves, presence of a ceiling net, and any past administration of IRS. All data were recorded on paper and entered later into Excel. GPS coordinates for each household were recorded using a Garmin GPS 60 device.
Spatial patterns of ITN use before and after distribution, as well as other factors, initially were assessed visually using maps produced from ArcGIS (version 10.1). GIS layers of environmental and geographic features were obtained from DIVA-GIS . Spatial autocorrelation was assessed using Moran’s I statistics. All statistical analyses were performed in R (version 2.15.2).
Patterns of association of age and ITN use were graphically assessed using a local regression smoothing methodology. Bivariate associations were tested and odds ratios and confidence intervals produced using logistic regression. After testing individual bivariate associations, a backwards selection procedure was used to create an optimal multivariate model.
Survey characteristics of households and people during pre-distribution (2011) and post-distribution (2012) of ITNs in Mbita District, Kenya
Number of individuals
Number of households
Median age of household members
Median number of people per household
Median number of nets per households
Mean number of nets per person in HH
Total percentage of people who slept under ITN the previous night
Mean percentage of people within households who slept under ITN the previous night
Condition and number of ITNs following distribution
Characteristics of ITNs in households sampled during post-distribution (2012) survey in Mbita District, Kenya
Total No. of Nets
Type of Net
In the House
Currently In Use
Determinants of ITN use
Results of the household survey
Ceiling net present
Home was sprayed in the last year (IRS)
Use of ITNs for purposes other than malaria prevention
Responded that the purpose of an ITN is to prevent malaria
Responded that the purpose of an ITN is to prevent mosquitoes from biting
Determinants of ITN use pre- and post-distribution
Numbers of people who lived in households with particular characteristics and percent of people who used ITNs are presented in Additional file 1. Bivariate logistic regression models for the pre- and post-distribution (Additional file 2) were constructed to allow for significance testing. Prior to distribution, males were less likely to sleep under an ITN than females [OR 0.47 (0.33, 0.67)]. The odds of using an ITN increased for every extra person residing in the home [OR 1.36 (1.16, 1.60)]. There were heterogeneities in ITN use among age groups, with 5 to 18 year olds having the lowest odds of using an ITN, compared with under 5′s [OR 0.36 (0.28, 0.48)].
Sleeping on the floor was associated with a decreased odds of using an ITN [OR 0.002 (0.001, 0.003)] along with sleeping in an open room [OR 0.002 (0.002, 0.003)] and having received IRS in the past [OR: 1.97 (1.25, 3.09)]. Individuals in households which were observed to use ITNs for purposes other than malaria control were more likely to sleep under an ITN [OR .2.69 (1.29, 5.63)]. Paternal education was not associated with ITN use pre-distribution while maternal education was. There was suggestive evidence that young people in households where the father was involved with fishing were more likely to use ITNs than households where the father was involved with other occupations. Maternal occupation was not associated with ITN use pre-distribution. Graded and inverse associations of material wealth with ITN use prior to the distribution programme were found.
Following ITN distribution, males were still less likely to sleep under ITNs than females [OR 0.61, (0.53, 0.70)]. As before, sleeping on the floor and sleeping in an open room were both highly associated with decreased odds of ITN use. It is also noted the similar age effects between the two distribution periods. 5 to 18 year olds were still the group least likely to use ITNs, compared with under 5′s [OR 0.25 (0.14, 0.41)]. Open eaves [OR 0.79 (0.00, 137.44)], an incremental increase in the number of rooms in the household, alternative uses of ITNs [OR 0.45 (0.00, 4082.40)], and indoor residual spraying [OR 2.58 (0.07, 93.32)] were no longer associated with ITN use. Maternal and paternal education and occupation were not associated with ITN use post-distribution. The positive association of material wealth with ITN use prior to the intervention disappeared following the mass distribution of ITNs. See Additional file 2 for complete results.
It is noted that in both the pre- and post-distribution phases, the odds ratios for sleeping location and room choice are very small. This is the result of including a random effect for household. Pre-distribution, sleeping on the floor [OR 0.24 (0.22, 0.26)] and sleeping in an open room [OR 0.22 (0.20, 0.25)] were associated with decreased odds of sleeping under and ITN. Likewise, post-distribution, sleeping on the floor [OR 0.31 (0.26, 0.36)] and sleeping in an open room [OR 0.30 (0.26, 0.35)] were associated with decreased odds of using ITNs. It should be noted that more than 91% of people who slept in an open room slept on the floor in both phases. When accounting for household effects of ITN use, which are a result of limited space and numbers of ITNs, sleeping on the floor was almost wholly associated with not using and ITN. Similarly, the large odds ratio was tempered somewhat when no including the random effect for household, but the age group of 30+ was still the group most likely to use ITNs compared to small children (pre [OR 1.83 (1.61, 2.08)], post [OR 1.69 (1.28, 2.24)]). When accounting for overall net use in the household, the effects of age are accentuated.
These results demonstrate that high levels of ITN coverage can be obtained through mass distribution of free nets, and that use compliance can be rapidly increased and maintained at least one year post-distribution. Inequities in coverage among socio-economic, educational and occupational groups can be erased through comprehensive no-payment provision of ITNs. Furthermore, problems of spatial heterogeneities in ITN possession can be successfully mitigated through a direct-to-household delivery strategy.
However, evidence suggests that even when sufficient numbers of nets are proactively provided to cover all residents in each household, patterns of failing to use them may persist. In this study, despite dramatically increased levels of ITN compliance overall, age-specific differences in ITN use remained unchanged. Heterogeneous age effects in ITN use have been noted by other researchers in a variety of contexts, including Kenya . However, it has been thought that distribution strategies which target children and pregnant women are responsible for such patterns of underuse. This study, where nets were provided to all members of the community, provides evidence to counter that assumption. In addition, practical issues of household sleeping arrangements and home construction continued to present barriers to full ITN compliance. Constraints on where and how to hang nets in common areas, a hurdle noted in other studies [24–26], are not, however, easily rectified.
Another concern that was discovered is the problem of ITN “leakage”, an issue that has been noted in other studies [27–29]. Although sufficient numbers of ITNs were given to cover all household members, the actual number of nets found one year later was much lower than what was initially provided. During related research, we found that freely distributed ITNs can be found in households other than those to which they were initially given (unpublished observation). Furthermore, even though nets are provided with the message that are specifically to be used for malaria prevention, household economic needs lead to nets being diverted to remunerable activities such as fishing or agriculture . It is unreasonable to expect that household heads, weighing numerous and sometimes conflicting pressures, will follow the requests of malaria researchers or public health workers. Thus, the possibility of leakage should be considered prior to mass distribution campaigns. Despite some net use for non-malaria prevention purposes, more than 90% of people slept under an ITN, and more than 97% of the nets found in the households were from this distribution campaign. Programmatically, this should be considered to be a success.
A “hot spot” analysis of ITN use was performed both before and after the distribution. It was found that before the distribution, high household level coverage of ITNs was found in the wet areas near the lake, possibly reflecting prior targeted intervention efforts. Further research, though, might also explore how mosquito density impacts ITN use. Household members in this area might tend to use nets more than in other areas simply due to an unbearable number of biting mosquitoes. Both before and after the intervention, ITN use in households along the paved highway was significantly lower than in other areas. Though it was not explored in this study, three possible explanations could be considered. First, households along the paved road often operate as storefronts so that sleeping spaces within the structure might be inadequate for hanging nets. It could also be the case that the storefronts only act as seasonal or temporary dwellings. Household members maybe have residences in other locations.
Maintaining consistent coverage of ITNs within transient households might present a challenge to malaria control programmes and should be considered for future research efforts. Second, it is possible that houses along the paved road are of sufficient quality to prevent mosquito entry through the presence of window screens, an important piece of data which was not collected. Third, the developed nature of this area might negatively impact breeding sites so that mosquito densities are low. More work should be done to assess the precise factors, which determine net use (or non-use) in this type of area.
Although net use was reported by a household member who may have under-reported use to obtain a free net, the age patterns that we observed agreed with other similar studies [5, 31, 32]. If actual use was understated this would have merely shifted the curve downward, but not differentially. That reported use following free distribution was nearly universal, though, is inconsistent with underreporting. In addition, surveillance teams visually confirmed whether nets were hanging, and different types of questions explored who was sleeping under nets. Thus, it is probable that this research accurately captured the general patterns of net presence and use.
Data from only two time points limits the ability to consider net use patterns in different seasons or over multiple years. Although data were collected over several months, this occurred at about the same time of year before and after net distribution. The tests for spatial patterns of ITN use, however, did not reveal patterns suggesting that sampling was time-dependent. Continued monitoring of net use should provide further insights into the duration of campaign impacts.
The extent of increased ITN coverage and use in this study provides reason for hope that such programmes will reduce malaria incidence. It is expected that Plasmodium transmission should decline, incidence of disease be lessened, and malaria-related mortality averted. However, given the very intense transmission of this area [33, 34], the persistence of diminished ITN use by specific age groups is cause for great concern. Like all African countries, Kenya’s age distribution is bottom heavy. If large numbers of young people are not using nets, even in the context of widespread availability, this subpopulation could contribute substantially to sustained transmission compromising control efforts.
This study was supported in part by the Global COE Program, Nagasaki University, Japan. It was also made possible through grants from the Rackham Graduate School at the University of Michigan, the University of Michigan International Institute and the Department of Epidemiology in the School of Public Health at the University of Michigan.
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