Coverage-Dependent Effect of Insecticide-Treated Curtains for Dengue Control in Thailand

Evidence on the effectiveness of insecticide-treated curtains (ITCs) for reducing densities of Aedes mosquitoes, the principal vectors of dengue, is scarce. In Laem Chabang southeast of Bangkok, Thailand, the Breteau Index (BI) (number of positive containers/100 houses) was 45 in October 2006. In March 2007, we distributed long-lasting ITCs in 22 clusters (2,032 houses) and selected 66 control clusters (661 houses). Routine control activities continued in all clusters. Six months after distribution, the BI was 25.8 and 77.6 in intervention and control areas, respectively (P < 0.001). Eighteen months after distribution, the BI was 21.8 and 23.8, respectively (P = 0.28). The average number of ITCs/house at cluster level was associated with the BI (P < 0.01) after six months, when 70.5% of households still used ITCs, but not at 18 months, when ITC coverage had decreased to 33.2%. Deployment of ITCs can result in considerable reductions in Aedes infestation levels, but the effect is coverage dependent.     

The cost of routine Aedes aegypti control and of insecticide-treated curtain implementation

Insecticide-treated curtains (ITCs) are promoted for controlling the Dengue vector Aedes aegypti. We assessed the cost of the routine Aedes control program (RACP) and the cost of ITC implementation through the RACP and health committees in Venezuela and through health volunteers in Thailand. The yearly cost of the RACP per household amounted to US$2.14 and $1.89, respectively. The ITC implementation cost over three times more, depending on the channel used. In Venezuela the RACP was the most efficient implementation-channel. It spent US$1.90 (95% confidence interval [CI]: 1.83; 1.97) per curtain distributed, of which 76.9% for the curtain itself. Implementation by health committees cost significantly (P = 0.02) more: US$2.32 (95% CI: 1.93; 2.61) of which 63% for the curtain. For ITC implementation to be at least as cost-effective as the RACP, at equal effectiveness and actual ITC prices, the attained curtain coverage and the adulticiding effect should last for 3 years.     

Residual insecticidal activity of long‐lasting deltamethrin‐treated curtains after 1 year of household use for dengue control

Objective To evaluate the residual insecticidal activity of the PermaNet^® curtains on Aedes aegypti after 1 year of use in Thai households and to assess the influence of sun and dust exposure, washing practices and detergent use. Methods We sampled UV‐protected PermaNet^® curtains made of a long‐lasting deltamethrin‐[55 mg/m²] treated polyester netting, before (10 curtains) and after 8 (10 curtains) and 12 months (66 curtains) of household use in a field site in Chon Buri, Thailand. We assessed the residual insecticidal activity of the curtains by standard WHO bioassay, using a deltamethrin‐susceptible insectarium Aedes aegypti strain. Results Mosquito mortality was 100% before distribution, 100% at 8 months and 98.2% (95% CI 97.9–98.5) at 12 months of use. Sunlight, hand‐washing and detergent use had no effect on the residual insecticidal activity after 12 months. However, the mosquito survival rate increased by a factor of 6.4 (95% CI 3.5–11.8) on machine‐washed curtains and by a factor of 2.0 (95% CI 1.4–2.9) on curtains not covered by dust. Conclusion The residual insecticidal activity of PermaNet® curtains remains high after 12 months use under field conditions.     

Determinants of uptake, short-term and continued use of insecticide-treated curtains and jar covers for dengue control

Objective To evaluate the acceptance and long‐term use of insecticide‐treated (IT) materials for dengue vector control. Methods In 2007, IT jar covers and/or curtains (PermaNet®) were distributed under routine conditions to 4101 households (10 clusters) in Venezuela and to 2032 households (22 clusters) in Thailand. The use of IT tools was measured at distribution (uptake), at 5/6 months (short‐term use) and at 18/22 months (continued use) after distribution. Determinants of use were assessed with logistic regression analysis. Results The uptake of IT curtains was 76.7% in Venezuela and 92.3% in Thailand. It was associated with being a resident for >5 years (OR Venezuela 3.0 95% CI 2.0–4.4; OR Thailand 3.5 95% CI 1.7–7.3) and with pre‐intervention use of ordinary curtains (OR Venezuela 2.2 95% CI 1.4–3.6). The continued use decreased significantly to 38.4% of households in Venezuela and 59.7% in Thailand and was, conditional on short‐term use, only determined by the perceived effectiveness of IT curtains (OR Venezuela 13.0 95%CI 8.7–19.5; OR Thailand 4.9 95% CI 3.1–7.8). Disease knowledge and pre‐intervention perception of mosquito nuisance were not associated with IT curtains’ uptake or use. The uptake of IT jar covers in Venezuela was 21.5% and essentially determined by the presence of uncovered jars in the household (OR 32.5 95% CI 14.5–72.6). Their continued use, conditional on short‐time use, was positively associated with the household use of Abate® (OR 7.8 95% CI 2.1–28.9). Conclusion The use of IT curtains rapidly declines over time. Continued use is mainly determined by the perceived effectiveness of the tool. This poses a real challenge if IT curtains are to be introduced in dengue control programmes.