This study assessed the physical integrity and insecticidal residue of bed nets distributed in two sub Counties of Kirinyaga County, Kenya eighteen months after mass distribution campaign of 2016. Additionally, the use and care for bed nets was evaluated. This study is novel because no other study has assessed care, use and chemical residue of nets in Kirinyaga County which is one of the endemic areas in Kenya mostly due to rice farming.
Net usage was high in the two sub counties of Kirinyaga County at 97.9% of the respondent reporting to have used the net the previous night. This is in line with earlier report of high net utilisation [31, 16]. This high rate of net usage has been found to decrease as the nets get older and the number of holes increases [5, 20,]. The high net utilization in the study area has led to speedy drop of malaria incidences in Kirinyaga County, where health facilities have reported a zero positive malaria case for a period of one year, according to unpublished report by department of health Kirinyaga County. This high net utilization is an indicator that people have accepted use of free nets [18, 19] in compliance to the guidelines issued during distribution. This high net usage could be due to round the year larva development, facilitated by rice irrigation farms.
The percentage of nets with at least one hole in this study was 47.9% after 18 months of use, and 1% of those with holes were too torn to offer personal protection. This small proportion of nets unable to offer personal protection changed when the nets surveyed were classified according to WHO criteria of serviceable and too torn nets. The results showed that 14.2 % of the nets were too torn. This is unlike what it had been shown in Uganda where considerable physical net damage (48-78% of nets) had occurred within one year of bed net use [21, 22]. This low percentage of torn nets in the current study could be accredited to the sensitization campaign carried out by the National Malaria Control Program (NMCP) through the Ministry of Health, on use, care and maintenance of bed nets, carried prior to net distribution [20, 10]. Education information campaign on net maintenance was seen to improve on net care and proper use as reported by Spencer et al. after a pre-distribution education campaign in South West Uganda [22].
Majority of the holes were found on the lower part of the net, with all the sides having almost the same proportions of holes. The main cause of holes on the lower side as reported was due to continuous tucking under the mattress and often, the net getting caught by rough edges. House environment (type of building material), and general handling contribute to bed net deterioration [20]. The uniform rate of deterioration on all the sides of bed nets in this study shows that the social economic status of the population is relatively the same. Deterioration of bed nets have been shown to be higher in poorer communities [4].
More than half of nets (85%), with at least one hole had not been repaired, as was the case in an Ethiopian study where very few households had repaired their nets [21]. When participants were asked why they had not repaired their nets, they reported not to know that a net needed repair. A net becomes less protective with increased number of holes even when treated with an insecticide [5].
The current study results shows that 81.7% of the nets supplied had survived, and serviceable according to WHO criteria which is encouraging after eighteen months of use. The only cause of net loss in the study area was due to net being given away to family members living far away [12]. The combination of insecticidal potency and the good physical condition demonstrates nets effectiveness in providing personal protection.
Nets were further categorised as “serviceable” and “too torn” nets (bed nets which requires immediate replacement) [12]. Classification of nets as serviceable (good and damaged nets) was arrived at using the pHI, shows that nets can inhibit mosquito bite even when they are in “damaged” status. This could be attributed partly to the repellent effect of the pyrethroid incorporated or coated in the nets [20].
The statistical difference between net deterioration and the manufacturer points underlying factors associated with defects during manufacturing.
In the current study, 3.1% of the nets were found in their original package. When owners were asked what they had been using, they reported to have been using nets given during the previous mass net distribution of 2011. This excess ownership of bed nets was also found by Githinji et al. in a study conducted in Western Kenya where more than half (63%) of the nets in their original package were provided during free mass net campaign [15]. Free mass net distribution campaign of 2006 made Kenya the country with highest number of net distributed at that time in Africa [23]. Sambe and others [4] reported that net owners keep excess nets in order to replace, once the existing nets in use become old.
1% of the nets in the current had been used for other purposes (mis-used) rather than protection. Higher rates of net mis-use had been reported by Mutuku et. al. in Kwale County, Kenya, where up to 21% of distributed nets had been mis-used [5, 23 and 24].
Social economic status of the community was not assessed, but majority of the houses visited were constructed either by wood or earth walled with planks. House material is a major contributor to the rate of net deterioration. This could possibly explain the cause of holes found on the upper part of the nets, explained as challenges faced during hanging. The net ability to offer protection from mosquito bite could have been compromised if the number of holes on the upper part of the net was big; since it has been shown that mosquitoes are more likely to enter bed nets from the upper part of bed net [32].
A safety measure considered during bed net manufacture is ensuring that if a spark lands on a net the burn should not exceed a few centimetres [6]. This could possibly explain why the holes caused by fire burn, were all size one holes.
Baseline concentration of the insecticide in the nets had a median surface concentration of; for α-cypermethrin treated nets 39.40 mg/m2 (IQR 39.15 – 42.10) and 6.98 mg/g (IQR 0.97 – 17.02) for permethrin treated nets (Table 4).
Different sides of a baseline nets had different amount of the pyrethroid. There was non-uniformity with any of the sides’ in different baseline nets. This could be attributed to a problem in the manufacturing process. During manufacture cooling and stretching of the polymer segregates permethrin to the fibre surface [25]. This could be responsible of low initial surface concentration in some parts of the net. This low surface concentration on the surface fibres of a net has also been reported [25, 30].
Insecticide content had decreased to 81.85% of the baseline concentration in α-cypermethrin treated nets. Some of the factors associated with insecticide decrease in a net are washing (and before complete regeneration occurs) and abrasion. The study did not assess the last time the nets were washed, but some of the nets were found drying after a wash on the survey date. This could have been a cause of low surface concentration in some of the nets; and in any event that the sampled net was less than two weeks since it was last washed. A complete regeneration of insecticide in a treated net from the sub surface of the fibres to the surface fibres requires approximately two weeks at 30 after washing [28].
Abrasion also lowers insecticidal concentration on the surface of a net [13]. This is likely to happen when tacking the net or when the net is being rolled up in the morning [7]. The findings on the net chemical residue are in line with most programmes where a net insecticidal activity last for at least three years. In a phase III evaluation study of LLINs, it was found that concentration as low as 1.3 mg/m2 of α-cypermethrin remaining in a net (from an initial concentration of 40mg/m2) is effective in killing mosquitoes [26].
Analysis of variance showed that a net chemical content is relatively the same for nets with different number of washes. A washed net would protect an individual just like an unwashed net. Every time a net is washed it loses some of its insecticidal content on the surface fibres, but a replacement of the washed insecticide from the sub-surface to the surface fibres occurs which makes a bed net to be effective throughout its life span of 3 years [27].
The study did not capture the “last time” the net was washed which is a potential limiting factor because we could not ascertain whether complete regeneration had occurred prior to analysis. Secondly due to lack of a validated data on the expected initial surface concentration of a baseline net we were not able to quantify the rate of loss after a net has been washed.