Variation of physical durability between LLIN products and net use environments: summary of findings from four African countries.

BACKGROUND: Physical durability of long-lasting-insecticidal nets (LLIN) is an important aspect of the effectiveness of LLIN as a malaria prevention tool, but there is limited data on performance across locations and products. This secondary analysis of data from the VectorWorks project from 10 sites in four African countries involving six LLIN brands provides such data. METHODS: A total of 4672 campaign nets from 1976 households were recruited into prospective cohort studies 2-6 months after distribution through campaigns and followed for 3 years in Mozambique, Nigeria, DRC and Zanzibar, Tanzania. LLIN products included two 100 denier polyester LLIN (DawaPlus® 2.0, PermaNet® 2.0) distributed in five sites and four 150 denier polyethylene LLIN (Royal Sentry®, MAGNet®, DuraNet©, Olyset™ Net) distributed in five sites. Primary outcome was LLIN survival in serviceable condition and median survival in years. Net use environment and net care variables were collected during four household surveys. Determinants of physical durability were explored by survival analysis and Cox regression models with risk of failure starting with the first hanging of the net. RESULTS: Definite outcomes for physical durability were obtained for 75% of study nets. After 31 to 37 months survival in serviceable condition varied between sites by 63 percentage-points, from 17 to 80%. Median survival varied by 3.7 years, from 1.6 to 5.3 years. Similar magnitude of variation was seen for polyethylene and polyester LLIN and for the same brand. Cox regression showed increasing net care attitude in combination with exposure to net related messages to be the strongest explanatory variable of survival. However, differences between countries also remained significant. In contrast, no difference was seen for LLIN material types. CONCLUSIONS: Variation in net use environment and net care is the main reason for differences in the physical durability of LLIN products in different locations. While some of these factors have been identified to work across countries, other factors remain poorly defined and further investigation is needed in this area. Grouping LLIN brands by similar textile characteristics, such as material or yarn strength, is insufficient to distinguish LLIN product performance suggesting a more differentiated, composite metric is needed.

Correlation of textile 'resistance to damage' scores with actual physical survival of long-lasting insecticidal nets in the field.

BACKGROUND: Attempts have been made to link procurement of long-lasting insecticidal nets (LLIN) not only to the price but also the expected performance of the product. However, to date it has not been possible to identify a specific textile characteristic that predicts physical durability in the field. The recently developed resistance to damage (RD) score could provide such a metric. This study uses pooled data from durability monitoring to explore the usefulness of the RD methodology. METHODS: Data from standardized, 3-year, prospective LLIN durability monitoring for six LLIN brands in 10 locations and four countries involving 4672 campaign LLIN were linked to the RD scores of the respective LLIN brands. The RD score is a single quantitative metric based on a suite of standardized textile tests which in turn build on the mechanisms of damage to a mosquito net. Potential RD values range from 0 to 100 where 100 represents optimal resistance to expected day-to-day stress during reasonable net use. Survival analysis was set so that risk of failure only started when nets were first hung. Cox regression was applied to explore RD effects on physical survival adjusting for known net use environment variables. RESULTS: In a bivariate analysis RD scores showed a linear relationship with physical integrity suggesting that the proportion of LLIN with moderate damage decreased by 3%-points for each 10-point increase of the RD score (p = 0.02, R2 = 0.65). Full adjustment for net care and handling behaviours as well as other relevant determinants and the country of study showed that increasing RD score by 10 points resulted in a 36% reduction of risk of failure to survive in serviceable condition (p < 0.0001). LLINs with RD scores above 50 had an additional useful life of 7 months. CONCLUSIONS: This study provides proof of principle that the RD metric can predict physical durability of LLIN products in the field and could be used to assess new products and guide manufacturers in creating improved products. However, additional validation from other field data, particularly for next generation LLIN, will be required before the RD score can be included in procurement decisions for LLINs.

Monitoring the durability of the long-lasting insecticidal nets Olyset® and PermaNet® 2.0 in similar use environments in Zanzibar.

BACKGROUND: Malaria transmission in Zanzibar has dramatically reduced in recent years but vector control interventions such as long-lasting insecticidal nets (LLIN) must continue to reach malaria elimination. To achieve this, the Zanzibar Malaria Elimination Programme needs actionable evidence of the durability of the LLIN brands distributed. This study compared physical and insecticidal durability of two LLIN brands: Olyset® and PermaNet© 2.0 in two similar districts on the islands of Unguja and Pemba. METHODS: This was a prospective cohort study of representative samples of households from two districts, recruited at baseline 4 months after the mass campaign. All campaign nets in these households were labelled and followed up over a period of 33 months. Primary outcome was the "proportion of nets surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from sub-samples of campaign nets. RESULTS: A total of 834 campaign nets (121% of target) from 299 households were included in the study. Definite outcomes could be determined for 86% of the cohort nets in Unguja (PermaNet® 2.0) and 89% in Pemba (Olyset®). After 33 months, physical survival in serviceable condition was 55% in Unguja and 51% in Pemba. Estimated median survival was lower in Pemba at all time points with 2.3-2.7 years compared to 3.1-3.3 yeas in Unguja. Multivariable Cox proportionate hazard models confirmed the difference between brands (p < 0.0001) and identified household net-care attitude (p = 0.007) and folding of hanging nets during the day (p < 0.0001) as significant determinants, in addition to exclusive use of nets by adults (p = 0.03) and use only over a finished bedframe (p = 0.01). Optimal insecticidal effectiveness was 80% or higher for both brands at all time points when both cone bio-assays and tunnel tests were applied. CONCLUSIONS: After 3 years of follow-up, Olyset® LLIN showed significantly lower physical survival compared to PermaNet® 2.0 LLIN even after adjusting for other variables of net-use environment and net handling. This suggests that the differences were driven by the textile characteristics of the LLIN brands.

Monitoring the durability of the long-lasting insecticidal nets MAGNet and Royal Sentry in three ecological zones of Mozambique.

BACKGROUND: Malaria prevention with long-lasting insecticidal nets (LLINs) has seen a tremendous scale-up in sub-Saharan Africa in the last decade. To sustain this success, it is important to understand how long LLINs remain in the households and continue to protect net users, which is termed durability. This information is needed to decide the appropriate timing of LLIN distribution and also to identify product(s) that may be underperforming relative to expectations. Following guidance from the U.S. President's Malaria Initiative, durability monitoring of polyethylene 150-denier LLIN (Royal Sentry® and MAGNet®) distributed during a 2017 mass campaign in Mozambique was implemented in three ecologically different sites: Inhambane, Tete, and Nampula. METHODS: This was a prospective cohort study in which representative samples of households from each district were recruited at baseline, 1 to 6 months after the mass campaign. All campaign LLINs in these households were labelled and followed up over a period of 36 months. The primary outcome was the "proportion of LLINs surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from subsamples of campaign LLINs. RESULTS: A total of 998 households (98% of target) and 1998 campaign LLIN (85% of target) were included in the study. Definite outcomes could be determined for 80% of the cohort LLIN in Inhambane, 45% in Tete, and 72% in Nampula. The highest all-cause attrition was seen in Nampula with 74% followed by Inhambane at 56% and Tete at 50%. Overall, only 2% of campaign LLINs were used for other purposes. Estimated survival in serviceable condition of campaign LLINs after 36 months was 57% in Inhambane, 43% in Tete, and 33% in Nampula, corresponding to median survival of 3.0, 2.8, and 2.4 years, respectively. Factors that were associated with better survival were exposure to social and behavioural change communication, a positive net care attitude, and folding up the net during the day. Larger household size negatively impacted survival. Insecticidal performance was optimal up to 24 months follow-up, but declined at 36 months when only 3% of samples showed optimal effectiveness in Inhambane, 11% in Tete and 29% in Nampula. However, 96% of LLIN still had minimal effectiveness at 36 months. CONCLUSIONS: Differences in median survival could be attributed at least in part to household environment and net care and repair behaviours. This means that in two of the three sites the assumption of a three-year cycle of campaign distributions holds, while in the Nampula site either continuous distribution channels could be expanded or more intense or targeted social and behaviour change activities to encourage net care and retention could be considered.

Comparing the durability of the long-lasting insecticidal nets DawaPlus® 2.0 and DuraNet© in northwest Democratic Republic of Congo.

BACKGROUND: Anecdotal reports from DRC suggest that long-lasting insecticidal nets (LLIN) distributed through mass campaigns in DRC may not last the expected average three years. To provide the National Malaria Control Programme with evidence on physical and insecticidal durability of nets distributed during the 2016 mass campaign, two brands of LLIN, DawaPlus® 2.0 and DuraNet©, were monitored in neighbouring and similar health zones in Sud Ubangi and Mongala Provinces. METHODS: This was a prospective cohort study of representative samples of households from two health zones recruited at baseline, 2 months after the mass campaign. All campaign nets in these households were labelled, and followed up over a period of 31 months. Primary outcome was the "proportion of nets surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from subsamples of campaign nets. RESULTS: A total of 754 campaign nets (109% of target) from 240 households were included in the study. Definite outcomes could be determined for 67% of the cohort nets in Sud Ubangi and 74% in Mongala. After 31 months all-cause attrition was 57% in Sud Ubangi and 76% in Mongala (p = 0.005) and attrition due to wear and tear was 26% in Sud Ubangi and 48% in Mongala (p = 0.0009). Survival in serviceable condition at the last survey was 37% in Sud Ubangi and 17% in Mongala (p = 0.003). Estimated median survival was 1.6 years for the DawaPlus® 2.0 in Mongala (95% CI 1.3-1.9) and 2.2 years for the DuraNet in Sud Ubangi (95% CI 2.0-2.4). Multivariable Cox proportionate hazard models suggest that the difference between sites was mainly attributable to the LLIN brand. Insecticidal effectiveness was optimal for DuraNet©, but significantly dropped after 24 months for DawaPlus® 2.0. CONCLUSIONS: In the environment of northwest DRC the polyethylene LLIN DuraNet© performed significantly better than the polyester LLIN DawaPlus® 2.0, but both were below a three-year median survival. Improvement of net care behaviours should be able to improve physical durability.

Monitoring the physical and insecticidal durability of the long-lasting insecticidal net DawaPlus® 2.0 in three States in Nigeria.

BACKGROUND: Following guidance from the US President's Malaria Initiative, durability monitoring of DawaPlus® 2.0 brand of long-lasting insecticidal net (LLIN) distributed during the 2015/16 mass campaign was set up in three ecologically different states: Zamfara, Ebonyi and Oyo. METHODS: This was a prospective cohort study of representative samples of households from each location, recruited at baseline, 1 to 6 months after the mass campaign. All campaign nets in the households were labelled and followed up over a period of 36 months in Zamfara and Ebonyi and 24 months in Oyo. Primary outcome was the "proportion of nets surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from sub-samples of campaign nets. RESULTS: A total of 439 households (98% of target) and 1096 campaign nets (106%) were included in the study. Definite outcomes could be determined for 92% of the cohort nets in Zamfara, 88% in Ebonyi and 75% in Oyo. All-cause attrition was highest in Oyo with 47% no longer present after 24 months, 53% in Ebonyi and 28% in Zamfara after 36 months. Overall only 1% of all campaign nets were used for other purposes. Estimated survival in serviceable condition of the campaign nets was 80% in Zamfara, 55% in Ebonyi (36 months follow-up) and 75% in Oyo (24 months follow-up) corresponding to median survival of 5.3, 3.3, 3.2 years, respectively. Factors associated with better survival were exposure to social messaging combined with a positive net-care attitude and only adult users. Failing to fold the net when hanging and having children under 5 years of age in the household negatively impacted net survival. Insecticidal effectiveness testing at final survey showed knock-down rates of 50-69%, but 24-h mortality above 95% resulting in 100% optimal performance in Ebonyi and Oyo and 97% in Zamfara. CONCLUSIONS: Results confirm the strong influence of net-use environment and behavioural factors in the physical survival of the same LLIN brand, which can increase the time until 50% of nets are no longer serviceable by up to 2 years.

Age and gender trends in insecticide-treated net use in sub-Saharan Africa: a multi-country analysis.

BACKGROUND: The degree to which insecticide-treated net (ITN) supply accounts for age and gender disparities in ITN use among household members is unknown. This study explores the role of household ITN supply in the variation in ITN use among household members in sub-Saharan Africa. METHODS: Data was from Malaria Indicator Surveys or Demographic and Health Surveys collected between 2011 and 2016 from 29 countries in sub-Saharan Africa. The main outcome was ITN use the previous night. Other key variables included ITN supply (nets/household members), age and gender of household members. Analytical methods included logistic regressions and meta-regression. RESULTS: Across countries, the median (range) of the percentage of households with enough ITNs was 30.7% (8.5-62.0%). Crude analysis showed a sinusoidal pattern in ITN use across age groups of household members, peaking at 0-4 years and again around 30-40 years and dipping among people between 5-14 and 50+ years. This sinusoidal pattern was more pronounced in households with not enough ITNs compared to those with enough ITNs. ITN use tended to be higher in females than males in households with not enough ITNs while use was comparable among females and males in households with enough ITNs. After adjusting for wealth quintile, residence and region, among households with not enough ITNs in all countries, the odds of ITN use were consistently higher among children under 5 years and non-pregnant women 15-49 years. Meta-regressions showed that across all countries, the mean adjusted odds ratio (aOR) of ITN use among children under 5 years, pregnant and non-pregnant women aged 15-49 years and people 50 years and above was significantly higher than among men aged 15-49 years. Among these household members, the relationship was attenuated when there were enough ITNs in the household (dropping 0.26-0.59 points) after adjusting for geographical zone, household ITN supply, population ITN access, and ITN use:access ratio. There was no significant difference in mean aOR of ITN use among school-aged children compared to men aged 15-49 years, regardless of household ITN supply. CONCLUSIONS: This study demonstrated that having enough ITNs in the household increases level of use and decreases existing disparities between age and gender groups. ITN distribution via mass campaigns and continuous distribution channels should be enhanced as needed to ensure that households have enough ITNs for all members, including men and school-aged children.

Evaluation of a continuous community-based ITN distribution pilot in Lainya County, South Sudan 2012-2013.

BACKGROUND: Continuous distribution of insecticide-treated nets (ITNs) has now been accepted as one way of sustaining ITN universal coverage. Community-based channels offer an interesting means of delivering ITNs to households to sustain universal ITN coverage. The objective of this study was to provide proof of concept for this channel. METHODS: A 9-month, community-based, distribution pilot was implemented beginning 1 year after a mass campaign in Lainya County, South Sudan from 2012 to 2013. Following social mobilization, community members could request an ITN from a net coupon holder. Eligibility criteria included having lost an ITN, giving birth outside of the health facility, or not having enough ITNs for all household members. After verification, households could exchange the coupon for an ITN at a distribution point. The evaluation was a pre/post design using representative household surveys with two-stage cluster sampling and a sample size of 600 households per survey. RESULTS: At endline, 78% of respondents were aware of the scheme and 89% of those also received an ITN through community-based distribution. Population access to ITNs nearly doubled, from 38% at baseline to 66% after the pilot. Household ownership of any ITN and enough ITNs (1 for 2 people) also increased significantly, from 66 to 82% and 19 to 46%, respectively. Community-based distribution was the only source of ITNs for 53.4% of households. The proportion of the population using an ITN last night increased from 22.7% at baseline to 53.9% at endline. A logistic regression model indicates that although behaviour change communication was positively associated with an increase in ITN use, access to enough nets was the greatest determinant of use. CONCLUSIONS: ITN access and use improved significantly in the study area during the pilot, coming close to universal coverage targets. This pilot serves as proof of concept for the community-based distribution methodology implemented as a mechanism to sustain ITN universal coverage. Longer periods of implementation should be evaluated to determine whether community-based distribution can successfully maintain ITN coverage beyond the short term, and reach all wealth quintiles equitably.