Monitoring of Fabric Integrity and Attrition Rate of Dual-Active Ingredient Long-Lasting Insecticidal Nets in Tanzania: A Prospective Cohort Study Nested in a Cluster Randomized Controlled Trial
2.1. Characteristics of the Long-Lasting Insecticidal Nets (LLINs) Tested
2.2. Study Area
2.3. Study Design
This study adopted a prospective cohort design, tracking nets over three consecutive years to evaluate the survivorship/attrition and fabric integrity of potential dual-active ingredient (dual-AI) LLINs in comparison to standard LLINs. After LLIN distribution, a census/enumeration of households in the hamlet was completed as part of the cRCT, and each household was given unique identification numbers. Selected study LLINs were recorded and labeled with a household number and net number one month post-distribution.
2.4. Sample Size and Sampling
Sample size calculations were conducted using the power log-rank command in Stata v.15.1. A total of 750 LLINs per net type from 5 clusters per arm (equivalent to 150 per cluster) allowed for a detection rate with a 9.4% absolute difference (hazard ratio = 0.8651) in LLIN attrition rates, assuming an attrition rate in the control of 70% over the 3 years. This calculation takes into account an intra-cluster correlation coefficient (ICC) of 0.05.
Following distribution, all selected nets were labeled with the household number and a net number to generate a master list. In each arm, up to three nets from each selected household (HH) (with a total of 250 HHs selected) were assessed in 5 clusters per arm (20 clusters in total). The study nets (750 per arm) were randomly sampled from the master list and evaluated for survivorship/attrition and fabric integrity at 6, 12, 24, 30, and 36 months post-distribution. The objective of the study was explained to head of the household before net inspections and those who agreed to participate in the study were interviewed about their socioeconomic status, housing materials, and the condition of the net through a structured questionnaire and templates for hole assessment.
2.5. Attrition Rate
2.6. Fabric Integrity
2.7. Data Analysis
All analyses were conducted using Stata version 18. Household characteristics were computed using proportional statistics. There were an additional 6 to 12 houses visited during the survey period that were not initially selected, and while these nets were included in the analysis of consent results, they were not considered in the assessment of functional survival.
2.8. Ethical Statement
This study was nested in a larger cRCT conducted in Misungwi. The cRCT received ethical approval from Kilimanjaro Christian Medical Collage, the National Institute for Medical Research (NIMR/HQ/R.8a/Vol.IX/2743), and the London School of Hygiene and Tropical Medicine (Ref: 16524). Informed consent to explain the purpose (objective) and nature of the study was read in Swahili and the local language if the household head did not understand Swahili. For those who consented, a signature or fingerprint was taken.
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