Durability, household usage and washing pattern of DuraNet© and Interceptor® long-lasting insecticidal nets in long-term field trials in India

SK Sharma; RS Yadav; HC Srivastava; RM Bhatt; CS Pant; MA Haque; U Sreehari; K Raghavendra

doi:10.4103/0972-9062.328974

RESEARCH ARTICLE

Year : 2021 | Volume : 58 | Issue : 3 | Page : 219-227

Durability, household usage and washing pattern of DuraNet^© and Interceptor^® long-lasting insecticidal nets in long-term field trials in India

SK Sharma¹, RS Yadav², HC Srivastava³, RM Bhatt⁴, CS Pant⁵, MA Haque⁶, U Sreehari⁷, K Raghavendra⁸
¹ National Institute of Malaria Research, Sector-8, Dwarka, New Delhi; CHC Dhakoli, Zirakhpur, Punjab, India
² Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland
³ National Institute of Malaria Research, Field Unit; 23, Gangotri Park Society, Indira Gandhi Road, Nadiad, Gujarat, India
⁴ National Institute of Malaria Research, Field Unit, Raipur, Chhattisgarh; B/401, Jalsagar Apartments, Nadiad, Gujarat, India
⁵ National Institute of Malaria Research, Field Unit; A/12, Sunrise Park, Petlad Road, Nadiad, Gujarat, India
⁶ National Institute of Malaria Research, Sector-8, Dwarka, New Delhi; H/139, Sector-2, Rourkela, Odisha, India
⁷ ICMR- National Institute of Malaria Research Field Unit, Poojanahalli, Bengaluru, India
⁸ National Institute of Malaria Research, Sector-8, Dwarka, New Delhi, India

Date of Submission	17-Aug-2019
Date of Decision	20-Oct-2020
Date of Web Publication	15-Feb-2022

Correspondence Address:
Dr. K Raghavendra
National Institute of Malaria Research, Sector – 8, Dwarka, New Delhi
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0972-9062.328974

Abstract

Background & objectives: Universal coverage of population with long-lasting insecticidal nets (LLINs) living in endemic areas inhabited by ethnic tribal communities or in difficult to reach areas was found effective for disease control where other interventions such as indoor residual spraying have limited success because of operational issues. Evaluation of different LLINs with varied insecticides and fabrics are being evaluated to meet the demand of new products. This study was undertaken on two brands of LLINs, DuraNet© and Interceptor® that varied in fabric and manufacturing technologies to assess the usability in field conditions for atleast three years.
Methods: In large-scale field trials DuraNet©, alpha cypermethrin incorporated polyethylene net, was evaluated in Odisha state while, Interceptor® net, alpha cypermethrin coated polyester net was evaluated in Chhattisgarh and Gujarat states for a period of three years following WHO guidelines. Durability, usage pattern and washing behavior were monitored through periodic surveys and physical examination of nets.
Results: Survivorship of both the nets was 84–100% and every night usage rate was >62% in all seasons. Washing frequency was largely within the prescribed limits. The proportion of DuraNet© with holes was 26.7% in year one 74% in year three. In Gujarat, proportion of Interceptor® nets with holes at six months was 33.3% increased to 87% in year three and in Chhattisgarh, 6.7% after six months to 93.3% after three years of use respectively.
Interpretation & conclusion: Both the nets revealed a useful life of three years under the field condition

Keywords: Long-lasting insecticidal nets; alpha cypermethrin; DuraNet©; polyethylene; Interceptor®; polyester; durability; vector control

How to cite this article:
Sharma S K, Yadav R S, Srivastava H C, Bhatt R M, Pant C S, Haque M A, Sreehari U, Raghavendra K. Durability, household usage and washing pattern of DuraNet^© and Interceptor^® long-lasting insecticidal nets in long-term field trials in India. J Vector Borne Dis 2021;58:219-27

How to cite this URL:
Sharma S K, Yadav R S, Srivastava H C, Bhatt R M, Pant C S, Haque M A, Sreehari U, Raghavendra K. Durability, household usage and washing pattern of DuraNet^© and Interceptor^® long-lasting insecticidal nets in long-term field trials in India. J Vector Borne Dis [serial online] 2021 [cited 2023 Mar 29];58:219-27. Available from: http://www.jvbd.org//text.asp?2021/58/3/219/328974

Introduction

Long-lasting insecticidal nets (LLINs) are considered an important intervention tool to prevent malaria transmission in malaria-endemic countries^[1]. These nets have replaced conventionally treated insecticide treated nets (ITNs) because of the operational problems associated with retreatment of nets. The LLINs are manufactured in the factory in which the insecticide is either incorporated into the fibers at the time of extrusion or coated on the fibers of the net using a binder. The insecticide is slowly released and the bio-efficacy is retained for at least 20 washes according to the standard WHO recommended protocol^[2]. Current WHO guidelines expect nets to retain biological activity for a minimum of 20 standard washes under laboratory conditions and a three-year minimum period of use under field conditions^[3]. However, service-able life of net depends on various factors in addition to durability and insecticide efficacy, such as attrition rate and damage to the net depends on the way of it is used in the household. Several reports have been published documenting variations in longevity between different brands of LLINs^[4],[5].

New brands of LLINs require field evaluation before they are recommended for use in malaria vector control programme, in collaboration with the WHO Pesticide Evaluation Scheme (WHOPES) and the LLIN-industry. In India, three different brands of nets - Olyset net (high density polyethylene net incorporated with the target dose of 1.0 g AI/m² of permethrin), PermaNet 2.0 (multi-filament polyester net coated with the target dose of 55 mg AI /m² of deltamethrin) and Interceptor® (multi-filament polyester net coated with the target dose of 200 mg AI/m² of alphacypermethrin) have been extensively field tested in multi-centre trials in different eco-epidemiological settings^[6],[7],[8]. Out of these three nets, Olyset Net and PermaNet 2.0 are in use in the operational malaria control programmes. DuraNet© is an alpha-cypermethrin long-lasting (incorporated into filaments) insecticidal net. Alpha-cypermethrin is incorporated into 150-denier, monofilament, high-density polyethylene fibres, with the target dose of 5.8 g AI/kg, corresponding to 250 mg of alpha-cypermethrin per square meter of the fabric. The results of Phase III evaluation of Interceptor® and DuraNet© were reviewed by the WHOPES and was given full recommendation for use in public health programme^[9],[10]. In this paper, results of large-scale (Phase III) evaluations of DuraNet© and Interceptor® nets undertaken in the states of Odisha (eastern Indian state), Gujarat (western Indian state) and Chhattisgarh (central Indian state) are reported. In Odisha, DuraNet© was evaluated in a malaria hyperendemic tribal area of Sundargarh district while Interceptor® net was evaluated in Kheda and Anand districts in Gujarat state and Kanker district in Chhattisgarh state to provide evidence-based guidance for the procurement of suitable nets for malaria control programme. The present study reports on the durability and fabric integrity of both the nets with respect to their usage pattern and washing behaviour by the community.

Material & Methods

Study area

Odisha: The DuraNet© study was conducted in Bisra block of Sundargarh District (21°36′-22°32′;N and 83°32′;- 82°22′;E). Odisha state in the eastern part of India is endemic for malaria^[11]. Five hamlets with 300 households having a population of 1382 (4.6 persons/family) were selected. The study population predominantly constituted ethnic tribal of Oram and Munda communities with a literacy rate of 52.3%. Most of the houses were made of mud walls and flooring with tiled roofs (87.5%) and only 12.5% houses were having cemented walls with asbestos roof. The average sleeping units per house was 2.5. People generally sleep in rooms in all seasons and quite often the elder members sleep in verandah or open courtyard of the house. Community owned nets were found in 26% of the houses and average net ownership at the time of baseline survey was 0.4 net per house.

Topographically, the area presents ideal ecological conditions for malaria transmission with undulating uplands intersected by forested hills, rocky streams, and paddy fields. The area is characterized by a tropical humid climate and receives rainfall between June and September from the ‘southwest monsoon’ and in December and January from the ‘northeast monsoon’. Average annual rainfall ranges between 160–200 cm and mean annual temperature ranges between 22°C to 27°C. The weather seasons are: hot dry summer from April to mid-June, monsoon from mid-June to September, autumn from October to November, winter from December to January, and spring from February to March. The maximum temperature during summer rises to 40–45°C and the minimum temperature during winter falls to 5–10°C. About forty percent of the area is covered with forests and is inhabited predominantly by ethnic tribal communities with poor socio-economic status.

Gujarat: The study was carried out in a rural area of the districts of Kheda (22°45′-22°75′N; 72° 41′-72°68′E) and Anand (22°34′-22°57′N; 72°56-72°93′E). Four villages, 3 in Anand and 1 in Kheda district having a population of 2117 (4.86 persons/ house) were included in the study. The villages in both the districts are well developed and connected by all-weather roads. Most villages in the area have a school and the literacy rate is about 70%. Agriculture is the major occupation and the main crops grown are paddy, groundnut, cotton, millet, banana, tobacco and potato. Almost every village has a milk co-operative society and all villages have respective local self government ‘Panchayat (village council). The average net ownership was 0.5 net/household. An. culicifacies is responsible for major malaria transmission with endophagic and endophilic behaviour.

Chhattisgarh: The study was carried out in selected villages of district Kanker (19°09′-20°06′N and 80°30′-81°15′E) which is predominantly a tribal district and is situated in the southern region of the state. Most part of the district consists of hills, and forest covers about 60% of the geographical area. The district receives a normal annual rainfall of 1100 mm with 60–70 rainy days and has a tropical climate. The villages are scattered and mostly inhabited by Gond tribe. Agriculture is the major occupation of the people and main crop grown in this area is rain fed paddy. Average net ownership was found to be 1.4 net/ house during baseline survey.

Study design, net specifications and distribution

The present study was a phase III community-based household randomized trial to determine the efficacy of DuraNet^© and Interceptor^® up to three years of continuous use under the field conditions. Before net distribution, a household census was undertaken in each village and houses were randomized through computer generated numbers and 300 randomized houses were earmarked for distribution of DuraNet©. All the 300 households participated in the study and there was no refusal. On an average 2 nets were given in each household to ensure full community coverage. The period of DuraNet© study was from July 2009 to June 2012. Interceptor^® trial in Gujarat and Chhattisgarh states was carried out from August 2008 to September 2011. Interceptor^® (1020) and nets treated conventionally (730) with alpha-cypermethrin at 40 mg AI/m² were distributed randomly among 875 households living in 11 villages in the states of Gujarat (4) and in Chhattisgarh (7).

The DuraNet^© used in the study were supplied by Clarke Mosquito Control, USA. The DuraNet© were of 100% high density polyethylene, warp knitted monofilament yarn, 145±5% denier, mesh 20 holes/cm², weight 45g/m², bursting strength of 450 Kpa, target dose of 250 mg/m² of alpha-cypermethrin. The nets used in the trial were white in colour with a size of length 180 cm, width 190 cm and height 150 cm.

The Interceptor® nets were supplied by BASF, Germany. These were 100% polyester, multifilament yarn, 75 denier, mesh 25 holes/cm² density 30 g/m², bursting strength of 245 KPa, target dose of 6.7 g/kg or 200 mg/ m² of Fendozin, a mixture of alpha-cypermethrin and a polymer binder applied at the production facility. The nets were white in colour and measured with a size of length 180 cm, width 160 cm and height 150 cm. At the time of distribution of nets, the adult person in the household was informed about the need for reporting any adverse effect of the nets, as well as appropriate use and maintenance of their nets.

Surveys and durability measurement

The standard WHO questionnaire was used to conduct community-based surveys to elicit information on perception/practices and adverse effects. The surveys were conducted in following two ways:

During the sampling of 30 nets (at the end of months 1, 6, 18 and 30) from randomly selected houses, an adult householder from each selected house was interviewed by door-to-door visit to assess perceived adverse or beneficial effects, net utilization pattern/ frequency of use, method and number of washes, type of detergent used, and physical integrity of the net (size and number of holes).
Annual surveys of all the households (at the end of months 12, 24 and 36) were conducted by door-to- door visits to record physical presence/absence of the net to estimate the annual attrition rate and fabric integrity of the nets available with them, besides information on their perceptions and practices as mentioned above. All available nets with the households were surveyed for their usage pattern (year-round, seasonally, every night and occasionally), frequency and method of washing, drying during the preceding six months, degree of dirtiness of the net (clean, a bit dirty, dirty and very dirty) and physical integrity/aspects of the nets viz., number, size and position of holes, number of repairs (stitches, knots and patches). Holes were categorized into 3 sizes viz., size 1-hole smaller than will allow thumb to pass through, size 2- a larger hole, but will not allow a closed fist to pass through and size 3- hole bigger than a closed fist.

With the introduction of recent concept of calculation of hole index, the holes of three sizes were weighted according to the average area of each hole category. For the hole size categories described above, the weights were taken as 1, 23 and 196, which correspond to the areas estimated on the assumption that the hole sizes in each category were equal to the mid-points. Holes were categorized into three sizes only as per the protocol approved by WHO for this study in 2008 and holes of size-4 as per the recent guidelines were not recorded.

Thus, the Hole index = (1 x no. of size-1 holes) + (23 x no. of size-2 holes) + (196 x no. of size-3 holes)

Ethical statement

Ethics Committee (IEC) of the National Institute of Malaria Research granted approval. The trials also received the approval of the Health Ministry Screening Committee (HMSC) of the Indian Council of Medical Research (ICMR), Govt. of India. The study population was informed in detail about the purpose of the study and a written informed consent was obtained from headperson of every household willing to participate in the study. A copy of the informed consent form was also provided to each household.

Results

Usage pattern and net survivorship

DuraNet^©

The percentage of nets found after one month of distribution was 100% and it was maintained even after 36 months of community use. After one month, nets were reported to be used every night by 93.4% householders. 84.2% of the respondents reported use of nets by hanging over the bed and remaining population used the nets by hanging over the sleeping mat on the ground. Surveys after 12, 24 and 36 months of all the households revealed year-round and every night net usage of 78.0, 55.6 and 61.7% respectively. This indicated significant acceptance of nets for use by the study population [Table 1]. None of the distributed nets were found missing during the surveys, thereby indicating zero attrition rate over a period of three years. The net usage rate also depended on mosquito nuisance during certain months but every night use of net remained >53% (range 53.3–93.4%). Seasonal and every night, and seasonal but occasional use of nets varied considerably 0.8–16.7% and 1.0–24.2% respectively [Table 1].

Table 1: Survivorship and pattern of usage (in percentage) of DuraNet^© and Interceptor^® nets by the households at three study sites

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Interceptor®

In Gujarat, survey carried out after one month revealed that 98.2% (856/872) of the distributed nets were found in place with the households and all the available nets were found to be in use. Nets were reported to be used round the year and every night by 95.6% of households. Most of the households (96.3%) reported use of nets by hanging over the bed. After six months, 61.7% households of the 60 surveyed (30 each with LLINs and ITNs) reported year-round and every night usage of nets [Table 1]. Survey after one year of net distribution revealed that the proportion of year-round and every night net usage had reportedly increased to 87.7% indicating significant acceptance of nets by the community. Attrition rate after one year was 0.9% (4/444) which rose to 3.3% (10/294) after two years and was found to be 0.4% (3/145) after three years of net distribution.

In Chhattisgarh, the percentage of nets found after one month of distribution was 95.5% (839/878) and 84.5% (742/878) of the nets were being used. Nets were reported to be used year-round and every night by 82.8% of households and 80.5% of them used the nets by hanging over the bed. The other mode of using the net was hanging over mat or mattress on the ground. After six months of net distribution, a second survey of 60 randomly selected households revealed that 75% used the net year-round and every night [Table 1]. Net usage was observed to have gone up to 82% after one year of net distribution. Attrition rate increased from 3.1% (14/452) after one year to 8.4% (21/250) after two years and to 17.7% (26/147) after three years of net distribution.

The net usage rate mostly depended on the feeling of mosquito nuisance by the inhabitants during different seasons. Except in the survey carried out after 18 months at Gujarat site, when the proportion of use of net every night was 36.7%, in all surveys carried out after 1 year, every night use of net remained >66% at both the study sites. Seasonal and every night use of net varied considerably (3.3–50%) at the Gujarat study site whereas it varied from 2.6 to 16.6% at the Chhattisgarh site showing different pattern of use by the communities.

Washing behaviour and frequency

Net washing frequency was ascertained through questionnaire-based surveys. Sometimes, the answers from housewives were vague and not clear but overall assessments were made at reaching some conclusions based on these surveys as given below:

DuraNet©

A total of 17% households washed their nets once a year, 60.0% at six monthly intervals, 6.7% at 4-month intervals, 10% at 3-month intervals and 6.7% at about monthly intervals. Survey after one month of net distribution revealed that only 0.45% of the nets were washed at least once as indicated by the soluble ink mark. Survey of 30 households after six months showed that 26% of DuraNet© are washed and the proportion of washed nets was 76.1%. The proportion of washed nets ranged from 83% to 95% after 18 to 36 months of net distribution.

Interceptor^®

A total of 12.4% households washed their nets once a year, 22.5% at six-monthly interval, 29.4% at 4-month interval, 11.5%, quarterly and 7.6% at a frequency of every 2 months. A proportion of 0.7% households each washed their nets at about monthly intervals. In Gujarat, survey of all households after one month of net distribution revealed that 3.8% were washed at least once. Survey after six months revealed that 23.3% were washed and the proportion of washed nets was 21.5% after one year of household use. Proportion of nets washed ranged from 70% to 96% after 18 to 36 months of distribution. In Chhattisgarh, only 0.7% of the used nets were washed at least once. Survey of 60 households carried out after six months of net distribution revealed that about 45% nets were washed. After one year 79.6% of nets were found to be washed. Proportion of nets washed ranged from 90% to 96.4% after 18 to 36 months of distribution. At all the study sites, 93–98% households used cold water for washing and dried their nets outdoors.

Use of soap or detergent powder

DuraNet©

A total of 93% of the households reported use of locally available commercial soap powder, 2% reported use of soap bar and 5% reported no use of any detergent for washing the nets. About 90% of households reported soaking of nets prior to washing and about 7% households reported rubbing of nets against rock/stone as per washing practices in the community.

Interceptor^®

Most of the households (55%, both sites combined) reported the usage of locally available soap powder, 13% reported use of soap bar, while 19.1% used local made soap and about 8.1% used the mix of powder + soap bar for washing the nets. About 4.4% households reported no use of any kind of powder and soap for washing the nets. In Gujarat, 19.3% (10-52.4%) households reported rubbing of nets with plastic bristle brush while washing whereas, none of the households reported such practice in Chhattisgarh in any of the surveys.

Physical attributes of nets

DuraNet©

Physical examination of 30 nets after six months revealed that 20% (6/30) of DuraNet^© had holes. The proportion of nets with holes after one year was 26.7% (8/30) which gradually increased to 43.3% (13/30) and 74% (37/50) after two and three years of net distribution respectively [Table 2]. The most significant increase was observed in holes of size-1 from 0.7 holes per net after six months to 6.7 holes per net after three years of net use. Most of the holes were on the lower half of the nets than on upper half or the roof during all the surveys. The mean hole index increased from 2.4 (95% CI: 3.47, 3.53) after six months to 92.9 (128.3, 141.0) after three years [Table 2].

Table 2: Physical condition of DuraNet© and Interceptor® nets at three study sites

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The number of holes on lower half ranged from 0.5 to 5.0 per net at different follow up intervals of six months to three years from the date of distribution of nets [Table 3]. The number of holes on the upper half ranged from 0.2 to 2.1 holes/net and those on the roof ranged from 0.03 to 1.4 holes/net. Only few nets were found with repairs in the form of stitches (0.07–0.38 per net) and knots (0.03–0.34), open seams (0.02/net) and none with patches. Holes due to fire ranged between 0.07–0.4/net during different intervals [Table 3].

Table 3: Physical aspects of DuraNet© and Interceptor® nets withdrawn at different intervals at three study sites

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Examination of physical aspect of nets after one month of distribution revealed that 95.2% of the total nets were found clean and the rest were a little dirty. Survey after six months showed that 13.3% nets were either clean or very dirty. The proportion of clean nets varied from 6.7% to 26.7% whereas that of very dirty nets was 3.3% to 26% during surveys undertaken after one year and thereafter every six months up to three years of household use of nets [Table 3].

Interceptor®

In Gujarat, survey after six months revealed that 33.3% (10/30) of Interceptor® nets had holes. After one year, 63.3% (19/30) of nets were found with holes. Majority of holes were on the lower side [Table 2]. Proportion of nets with any holes increased from 33.3% after six months to 87% after three years. The most significant increase was observed in holes of size-1 from 2.5 holes per net after six months to 26.5 holes per net after three years. On an average the number of holes of size-2 per net increased from 0.5 after six months to 5.9 holes per net after three years and that of size-3 from 0.3 to 1.1 respectively. The mean hole index increased from 33.6 (95% CI: -19.9, 87.1) after six months to 377.8 (70.7, 684.8) after three years.

Physical examination of 30 nets after six months at Chhattisgarh study site revealed that proportion with any holes was 6.7 (2/30) which gradually increased from 33.3% after one year to 63.3% and 93.3% after two and three years of distribution respectively. The mean hole index increased from 7.3 (95% CI: -5.5, 20.1) after six months to 116.4 (60.2, 172.1) after three years of household use of nets [Table 2].

In Gujarat the number of holes on the lower half ranged from 0.8 to 23.2 per net at different follow up intervals [Table 3]. The number of holes on the upper half ranged from 0.4 to 10.4 holes/net and those on the roof ranged from 0.5–7.7 holes/net. A few nets were found with repairs in the form of stitches (0.6–1.6 per net) and knots (0.5–1.0 per net), open seams (1.7/net), none was with patches and damaged due to fire at different intervals [Table 3].

Survey of all households after one month of distribution revealed that 26.4% of all the nets were clean. After six months, the examination of 30 nets revealed that 33.3% were clean [Table 3] and 20% were very dirty. Proportion of very dirty nets varied from 16.7% to 43.3% in surveys carried out after one year and thereafter every six months up to three years of distribution.

In Chhattisgarh, the number of holes on the lower half ranged from 1 to 12.7 per net at different follow up intervals. The number of holes on the upper half ranged from 0.5-4.3 holes/net and those on the roof ranged from 0.7–2.1 holes/net. Quite a few LNs were found with repairs in the form of stitches (0.3–2.2 per net) and knots (0.2–1.0 per net), open seams (0.05–0.3) and none with patches. Hole due to fire was recorded in one net each in survey carried out after 18 and 30 months [Table 3].

In Chhattisgarh, survey of all households after 1 month of net distribution revealed that 95.1% of the total nets distributed were clean. After six months, the survey of 30 households with LNs revealed that 46.7% nets were clean while 16.7% were found to be very dirty. Proportion of very dirty nets varied from 3.3% to 16.7% in surveys undertaken after one year and thereafter every six months up to three years of net distribution [Table 3].

Perceived side effects

DuraNet^©

In a survey carried out after one month of the net distribution, the proportion of households reported transient side effects while coming in contact for the first time with nets was 64.2% (212/330). There were complains of skin irritation (35.5%), eye irritation (8.7%), itching (14.7%), suffocation (0.6) and rashes on body (0.9%). However, these effects were only transitory in nature lasting for few hours of the first usage and subsided upon washing of the affected body parts. 39.6% respondents reported no adverse effect.

Interceptor^®

In Gujarat, about 34% (149/436) households reported transient side effect in the form of skin irritation at the time of first survey carried out after one month of net distribution. No other side effects were reported by householders in any of the subsequent surveys. In a survey carried out after one month of net distribution in Chhattisgarh the proportion of households reporting transient skin irritation, itching sensation after first time usage of nets was 27% (119/439). Most of the users reported transient side effects at the time of removing the net from the original packing and handling it for first time. All the reported side effects subsided within one or two hours of their own or upon washing of the affected body parts.

Discussion

The role of long-lasting insecticidal nets in controlling malaria in different eco-epidemiological situations is very well documented^{[12],[13],[14]}. However, successful malaria control through LLINs not only depends upon the chemical efficacy of the nets but also on the quality of thread for manufacturing of nets, pattern of use and washing practices of the community thereby leading to the useful life of the net for effective protection against mosquito bites. Keeping these factors in perspective the present studies were undertaken in India following the standard WHO guidelines and procedures^[2].

The most encouraging aspect which came out of the present study was 100% survivorship of the distributed DuraNet© over a period of three years. After three years, a majority of Interceptor® nets were found to be retained (Gujarat: 99.6% and Chhattisgarh: 84.3%) and used (68% and 77.2% respectively) in whatever condition they were at both the study sites. This shows a very high level of net survivorship, usage rate and acceptance of the nets.

In Ethiopia, the net attrition rate was as high as 32% over three years^[15]. The night usage rate of net remained >53% (range 53.3–93.4%), thereby suggesting very high level of net usage rate and acceptance of the nets. In studies carried out in Uganda, 86% of nets were being regularly used by inhabitants even after three years^[16]. The comparative lower usage found in the present study may be due to prevailing hot weather conditions during most part of the year, except colder months from December–February and absence of nuisance insects owing to the adverse climatic conditions.

In Odisha, majority of the householders washed their nets twice a year. However, about 7% households washed their nets at about monthly intervals. Most households use fire wood for cooking resulting in the settling of smoke soot over the nets thereby having dirty look, which was considered to be unhealthy. The washing instructions given to the net owners were complied by most of the households as washing was done mostly with cold water and nets were put for drying outdoors under shade. However, contrary to instructions, about 7% households reported rubbing of nets against rock/stone as per washing practices in the community. As many as nine brands of soap powders were found to be used for washing of nets. A very high frequency of washing was observed in certain communities at Chhattisgarh site owing to cultural practices with a washing frequency of every month in 0.7% households. Thus, these nets would have been washed at least 12 times a year, which is more than the recommended washes for an LLIN during its effective life and reported washing frequency ranging from <2^[15] and 5–7^[17] washes per year. As many as 13 brands of locally manufactured soap bar and soap powder were used for washing the nets. The households at both the study sites are habitual of sweeping the mud floor of houses daily and burning of wood for cooking resulting in settling of dirt and shoot over the nets. The reason for more frequent washes of nets in certain houses was thus related with the dirty look of the nets which was considered to be unhygienic and socially unacceptable similar practices have also been reported in urban Dar-es-Salaam^[18].

Durability was measured by determining the hole index based on number of holes of three different sizes. The mean hole index increased from 2.4 after six months to 92.9 after three years of household use of DuraNet©, which was significantly lower than reported earlier in a study on Interceptor® nets in India^[19] thereby suggesting better upkeep of DuraNet© by the community. In the present Interceptor^® trial at two sites in India, the mean hole index increased from 33.6 after six months to 377.8 after three years in Gujarat and in Chhattisgarh from 7.3 after six months to 116.4.

In Chad, proportionate hole index was used to assess net durability in Interceptor^®, Olyset and PermaNet after one year of household use, and 25% had a hole index greater than 300; these nets were classified as “unserviceable and irreparable”. The remaining nets had proportionate hole indices in the middle ranges of 25–174 and 175–299 and were classified as in partial service^[20]. In the present study, repairs of the nets were also undertaken by the users although the number of nets repaired was not significant. Low repair rates were also reported by different studies in Uganda, Ethiopia, Ghana, and Peoples Democratic Republic of Lao^{[16],[21],[22],[23]}. There were no safety issues with the use of nets as the perceived side effects were only transitory in nature as also reported earlier while using them for the first time^[7].

The present observations on the use rate, washing behaviour, physical aspect and durability of DuraNet© and Interceptor® nets showed that community acceptance and quality of nets was good as was evident from large number of nets being found in useable condition after three years in spite of moderate to harsh climatic conditions prevailing at the study sites in India. Thus, it can be stated that these nets can have a prescribed useful life of at least three years and may be used as an effective intervention tool in a community-based operational malaria control programme.

Conclusion

Phase III evaluation of DuraNet^© and Interceptor^® nets revealed a useful life of at least three years under the prevailing field conditions at three different sites in India. The net survivorship over a period of three years was 84–100% and the net usage rate varied with seasons and was related to perceived mosquito nuisance, but every night use of net was more than 62% in all the seasons. Washing frequency was largely within the prescribed limits except for a small proportion washing the nets every month or so using various brands of local soap powders and bars. Therefore, both DuraNet^© and Interceptor^® nets holds a promise to be used as an effective vector control tool in the Indian operational malaria control programme particularly in malaria endemic areas inhabited by ethnic tribal communities and other difficult to reach areas where intervention tools such as indoor insecticide residual sprays have limited success because of difficulty in operational implementation and logistics.

Acknowledgements

Our sincere thanks are also due to the study population as well as to local leaders, heads of village councils, Accredited Social Health Activist (ASHA) and field staff of the Community Health Centre for their cooperation during the field surveys. Technical support provided by the staff at the National Institute of Malaria Research, New Delhi and Field Units at Nadiad, Raipur and Rourkela is gratefully acknowledged. Authors thankfully acknowledge WHOPES for providing financial and technical support.

Conflict of interest: None

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