ABSTRACT.
The use of household insecticides in the formulation of mosquito coils and vaporizers is common among the public to protect against mosquito-borne diseases. However, information regarding the use of these commonly practiced household insecticides is scarce in Sri Lanka. A questionnaire-based survey was directed to 600 households in Colombo, Gampaha, Kandy, Kalutara, Jaffna, and Galle districts in Sri Lanka. Household insecticides were used by the majority of the respondents (57.0%), and electric liquid vaporizers (46.7%) and mosquito coils (45.7%) were the commonly used forms. The active ingredients in mosquito coils were d-trans-allethrin (w/w 0.12%), metofluthrin (w/w 0.005%), and dimefluthrin (w/w 0.01%); in liquid vaporizers, they were prallethrin (w/v 1.24% and w/v 1.26%) and transfluthrin (w/v 0.9%). The majority of the household insecticide consumers were moderately satisfied with the effectiveness of the products (68.6%), and most of the participants used household insecticides daily (35.5%), especially during the evening (41.6%). Most of the consumers were unaware of the chemicals included in household insecticides (62.8%). Mosquito coils were abundantly used by rural area participants (75.8%), whereas liquid vaporizers were the most common among the urban participants (56.4%). The findings indicate that demographic and socioeconomic factors influence household insecticide practices. To our knowledge, this study reveals the use of household insecticides to control mosquitoes for the first time in Sri Lanka and highlights the importance of awareness programs and the proper utilization of these products.
INTRODUCTION
Vector-borne diseases are one of the major global public health threats, accounting for more than 17% of all infectious diseases and are responsible for more than 700,000 deaths each year globally.1 Mosquito-borne diseases such as dengue, chikungunya, malaria, yellow fever, and Zika pose a significant threat to human populations in many tropical and subtropical regions.1 Dengue in particular, has seen a 30-fold increase in global incidence over the past 50 years, making it the most rapidly spreading mosquito-borne viral disease.2 Dengue has evolved from a sporadic disease to a major public health problem due to its increased geographical extension, number of cases, and disease severity.3
Sri Lanka has experienced more than 50 years of dengue virus transmission,4 and dengue is considered hyperendemic in Sri Lanka, with the circulation of all four dengue virus serotypes.5 Large epidemics occur regularly, affecting the entire population of the island. In 2019, 104,500 cases were reported to the health authorities, with approximately 20% of dengue fever cases originating in the Colombo district.6
Integrated vector management is a strategic approach promoted by the WHO to control mosquito vectors. This strategic approach aims to reduce disease transmission by minimizing mosquito breeding through source reduction and decreasing human–vector contact.7 To reduce such contact, the WHO recommends using barriers such as insect screens, closed doors and windows, long clothing, space-spraying with insecticide, and household insecticide use.7 Personal or household insecticide products are prominent among these barriers. Taking personal protective measures against mosquito bites may prevent these diseases and reduce mosquito annoyance and itching.
Household insecticides are formulated mainly in the form of mosquito coils, liquid vaporizers, aerosols, and mats.8–11 These insecticide products are easy to use and obtain because they are available in local grocery shops, supermarkets, and other commercial outlets.9,12 The general public often uses them as personal protection around their homes and worksites to avoid mosquito bites.10,12 Indoor premises are expected to be the primary site for human exposure to the dengue virus in Sri Lanka because Aedes aegypti, the major dengue vector in Sri Lanka, rests, blood feeds, mates, and reproduces mainly indoors.13
Although pyrethroid-based household insecticides can induce adverse health effects with chronic exposure,10 mosquito coils and vaporizers are commonly used as personal protection methods to avoid mosquito bites. Several brands of household insecticides to control mosquitoes are available on the Sri Lankan market, and local people commonly use these products. However, increasing dengue incidences each year suggest that vector control efforts are futile. Community participation is one of the major roles in controlling dengue and other disease-carrying mosquito vectors. Community participation, in turn, depends on people’s awareness, knowledge, and practices related to the disease and its prevention.14 Several studies have been conducted to evaluate community knowledge, attitude, and practices to prevent dengue and other mosquito-borne diseases in Sri Lanka.15–18 However, we were unable to trace any previous comprehensive studies regarding household insecticide practices and usage patterns in Sri Lanka, and thus scientific details are scarce regarding whether the community uses household insecticide practices properly to control mosquitoes or needs education on the proper use of these products. The success of personal protective measures largely depends on consumers’ access to, acceptability, and proper use of them.19 Thus, it is of utmost importance that people be aware of the proper use of household insecticides.
In the present study, a questionnaire-based survey was conducted to fill this gap and gain a better understanding of household insecticide practices, consumer’s perspectives, and the influence of the demographic and socioeconomic factors (sex, urbanized level of the area, education level, and monthly income) on the use of commercial household insecticides for mosquitoes in Sri Lanka.
MATERIALS AND METHODS
Study design.
A preliminary survey was conducted to identify the popular household insecticides in the market; based on that data, the three main commonly available brands of household insecticides were selected. A questionnaire was prepared using the commercial brand names for ease of identification, but due to ethical concerns, the main active ingredients of the products are used in this article instead of brand names.
The questionnaire was administered in the three official languages of Sri Lanka (English, Sinhala, and Tamil) and was conducted via the online platform to collect data by sharing the Google form link via WhatsApp, e-mail, Facebook, and Telegram in February–March 2021. However, because an online survey was not familiar to the older adult group (older than 50 years old) and rural populations, questionnaires were printed and distributed in each district from November to December 2021 (Supplemental Document 1).
Study area.
Districts that recorded the highest cumulative dengue incidences in 2019 based on the data from the epidemiology unit were selected as the study sites. Supplemental Figure 1 shows the six main dengue high-risk districts Colombo (20,718), Gampaha (16,573), Kandy (8,940), Kalutara (8,395), Jaffna (8,261), and Galle (7,378).6 According to census reports in 2011, Colombo is the most populated district (2,324,349), where both the administrative capital (Sri Jayewardenepura Kotte) and the commercial capital (city of Colombo) of the country are situated. Gampaha and Kalutara districts border the Colombo district and are located in the western region of the country. Jaffna and Galle districts are situated in the northern and southern parts of the island, respectively, and the Kandy district represents the central region. Not all of these districts are fully urbanized; some parts consist of semiurban and rural areas.
Study participants.
The participants were from selected districts at high risk for dengue and were older than 18 years (inclusion criteria) because the questionnaire contains several questions that could be understood and correctly answered only by adults with specific experiences. Participation was voluntary, and participants could ask the investigator any questions at any time. The investigator’s contact details were included in the questionnaire. In addition, participants had the freedom to withdraw from the study at any time.
The questionnaire was directed at 600 households located in the six main dengue high-risk districts with the aim of collecting at least minimum of 50 eligible responses from each district because it is recommended that a minimum 30 samples is available to obtain a normal distribution. Only 521 responses were included in the analysis and others were rejected because they did not meet inclusion criteria.
Participants were informed in writing about the main objective of the project and the project investigators, assured that there would be no harm from participation in the project and that participation was voluntary, and told of the benefits to the community from their participation. The information was read or clarified upon participant request, and their consent was granted after indicating they fully understood.
The questionnaire was mainly prepared to collect data regarding the consumers’ satisfaction and usage of the products, the influence of the demographic and socioeconomic factors (sex, urbanized level of the area, education level, and monthly income) on their use and the local public knowledge about the chemicals used in those commercial household insecticide products.
Data management and statistical analysis.
The information recorded was confidential, and the questionnaire was anonymous. All data collected were entered into Google Forms and exported to Microsoft Excel 2010. By using the pivot table option of Microsoft Excel, all data were summarized into subgroups. All summarized data were statistically analyzed using a χ2 test to test the associations using minitab version 2017. A P-value ≤ 0.05 was considered statistically significant.
Ethical approval.
The study protocol was reviewed and approved (Ref No.: 44/20) by the Ethics Review Committee of the Faculty of Medical Sciences, University of Sri Jayewardenepura, Gangodawila, Nugegoda, Sri Lanka.
Secondary data collection.
The annual importation of household insecticide chemicals to the country in 2020 was collected from the Office of the Pesticides Registrar.
RESULTS
Six hundred households were included in the survey, the majority of which (521 responses) were from the dengue high-risk six districts. The highest number of responses (n = 178) were received from Colombo district (34.2%) and the lowest number (n = 55) from Jaffna district (10.6%). A total of 15.5% of responses were from Galle (n = 81), 14.6% from Kandy (n = 76), 13.8% from Gampaha (n = 72), and 11.3%. of participants were from the Kalutara district (n = 59).
Dengue incidence and control measures.
A high percentage (86.1%, n = 447) of respondents and/or any of their family members had no history of dengue. The highest number of respondents who had a history of dengue fever was from the Kalutara district (25.4%, n = 15), followed by Galle (14.8%, n = 12), Gampaha (13.9%, n = 10), Colombo (12.9%, n = 23), Kandy (11.8%, n = 9), and Jaffna (5.7%, n = 3).
Demographic and socioeconomic characteristics of the participants.
Supplemental Table 1 shows the demographic and socioeconomic characteristics of the survey participants. The majority (75.5%) of the participants from all six districts were female, and 24.5% were male. The highest percentage (79.2%) of respondents were between 18 and 30 years old. Among the heads of household, 39.5% were graduates, and 36.8% had secondary education as their highest level of education.
Among the 521 respondents, 507 (97.3%) were comfortable sharing their monthly income. It was categorized as follows: monthly income less than rupee (Rs.) 40,000 as lower-income households, between Rs. 40,000 and 80,000 as middle-income households, and more than Rs. 80,000 as higher-income households. Most of the participating households from Galle (39.8%), Gampaha (47.1%), Kalutara (40.5%), and Kandy (40.5%) districts reported being a middle income household. More respondents from the Colombo district (42.6%) were from higher-income households (more than Rs. 80,000). In comparison, most of the participating households from Jaffna district (50.9%) belonged to lower income households (less than Rs. 40,000).
Most of the responses were from semiurban residents (50.5%), followed by urban (36.2%) and rural households (13.3%). More than half of the respondents from the Colombo district (55.1%) lived in urban areas, whereas most of the other districts’ participants belonged to semiurban areas.
Insecticide practices to control mosquitoes.
Table 1 shows the types of insecticides used to control mosquitoes. Insecticide thermal fogging was not done in the majority (51.4%) of the participants’ houses; only 32.6% of the surveyed households had undergone fogging within the previous 2 years (2019 and 2020), and among them, a major share (39.0%) was distributed in the Kalutara district. More than half (57.0%) of the participants used household insecticides to control mosquitoes. Half of the respondents (50.0%) in the Kandy district did not use any household insecticide for mosquitoes. In the other five districts, most participants used household insecticides to combat mosquitoes.
Table 1.
Applications of insecticides taken to control mosquitoes
| Control practices | Colombo (%) | Galle (%) | Gampaha (%) | Jaffna (%) | Kalutara (%) | Kandy (%) | Total (%) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| When was fogging applied to your home? | ||||||||||||||
| A few days ago | 7 | (3.9) | 1 | (1.2) | 0 | (0.0) | 0 | (0.00) | 2 | (3.4) | 0 | (0.0) | 10 | (1.9) |
| A few weeks ago | 2 | (1.1) | 0 | (0.0) | 0 | (0.0) | 2 | (3.8) | 0 | (0.0) | 2 | (2.6) | 6 | (1.2) |
| A few months ago | 27 | (15.2) | 8 | (9.9) | 4 | (5.5) | 4 | (7.6) | 2 | (3.4) | 1 | (1.3) | 46 | (8.9) |
| 6 months ago | 6 | (3.4) | 4 | (4.9) | 3 | (4.2) | 8 | (15.1) | 0 | (0.0) | 0 | (0.0) | 21 | (4.0) |
| Within 2 years | 63 | (35.4) | 26 | (32.1) | 26 | (36.1) | 11 | (20.7) | 23 | (39.0) | 20 | (26.3) | 169 | (32.6) |
| Never | 73 | (41.0) | 42 | (51.9) | 39 | (54.2) | 28 | (52.8) | 32 | (54.2) | 53 | (69.8) | 267 | (51.4) |
| Are you using any commercially available household insecticides to control mosquitoes? (Example: mosquito coil, vaporizer, aerosol) | ||||||||||||||
| Yes | 92 | (51.7) | 51 | (63.0) | 41 | (56.9) | 40 | (75.5) | 34 | (57.6) | 38 | (50.0) | 296 | (57.0) |
| No | 86 | (48.3) | 30 | (37.0) | 31 | (43.1) | 13 | (24.5) | 25 | (42.4) | 38 | (50.0) | 223 | (43.0) |
| If “Yes,” in which formulation? | ||||||||||||||
| Mosquito coil | 40 | (43.5) | 17 | (36.2) | 21 | (51.2) | 28 | (70.0) | 10 | (30.3) | 16 | (34.8) | 132 | (45.7) |
| Liquid vaporizer | 44 | (47.8) | 27 | (57.4) | 16 | (39.0) | 11 | (27.5) | 20 | (60.6) | 27 | (58.7) | 135 | (46.7) |
| Aerosol | 8 | (8.7) | 3 | (6.4) | 4 | (9.8) | 0 | (0.0) | 2 | (6.1) | 3 | (6.5) | 20 | (6.9) |
| Mat | 0 | (0.0) | 0 | (0.0) | 0 | (0.0) | 1 | (2.5) | 1 | (3.0) | 0 | (0.0) | 2 | (0.7) |
The liquid vaporizer was the most common product used by the respondents of Colombo (47.8%), Galle (57.4%), Kalutara (60.6%), and Kandy (58.7%) districts. In contrast, mosquito coils were the most widely used household insecticide in the Gampaha (51.2%) and Jaffna districts (70.0%). A minority of the participants used aerosol (6.9%) in all districts, and only 0.7% of respondents used the mat.
Three active ingredients were available in the local market from three brands; the distribution of the use of the brands of liquid vaporizers is shown in Figure 1. The majority of the liquid vaporizer consumers used prallethrin (w/v 1.24%) (83.7%), and prallethrin (w/v 1.26%) was used by 80.0%. A total of 40.0% of the liquid vaporizer consumers never used transfluthrin (w/v 0.9%).
Figure 1.
Distribution of the use of different liquid vaporizer brands by participants.
The respondents commonly used three brands of mosquito coils with three active ingredients (Figure 2). A higher percentage of mosquito coil consumers used d-trans-allethrin (w/w 0.12%) (87.1%); 72.0% used mosquito coils containing dimefluthrin (w/w 0.01%), and 64.4% used metofluthrin (w/w 0.005%). Most of the respondents (68.6%) mentioned moderate satisfaction with commercially available household products. In comparison, 20.0% had poor satisfaction, and only 11.4% had higher satisfaction regarding the effectiveness of a product (Figure 3).
Figure 2.
Distribution of the use of different mosquito coil brands by participants.
Figure 3.
Overall consumer satisfaction with commercially available products.
Supplemental Table 2 shows the patterns of household insecticide practices. Most consumers (41.6%) used household insecticides during the afternoon and evening (3:00–6:00 pm) followed by the whole night (starting at 6:00 pm; 24.3%). A lower percentage of respondents (3.0%) used household insecticides in the morning (6:00–10:00 am). A total of 22.3% of the participants used household insecticides only during sleeping time, and 8.8% used them just before sleeping. A total of 35.5% of consumers used household insecticides daily, whereas 30.4% used them only during the high mosquito breeding seasons. The majority (68.2%) of the household insecticides to control mosquitoes were used to protect all the family members from mosquito bites. Some people (31.8%) used household insecticides to avoid mosquito bites for both family members and pets. None of the participated consumers use household insecticides only for pets.
Supplemental Table 3 displays consumers’ and nonconsumers’ knowledge of the chemicals used in household insecticides. Out of all the participants, a higher percentage of consumers did not have knowledge (62.8%) about the chemicals used in household insecticides to control mosquitoes; 46.2% of the nonconsumers respondents knew about the chemicals.
Less/no mosquito nuisance was the main (44.8%) reason the nonconsumer participants were not using any household insecticide to control mosquitoes, although 30.5% of the nonconsumers were concerned about their safety (Supplemental Figure 2). In addition, allergies, smell, high cost, and limited knowledge were some of the reasons (Supplemental Figure 2), and 3.6% of nonconsumers used alternative strategies to avoid mosquitoes, such as natural repellents, fans, and bed nets, which made them nonconsumers of household insecticides.
Urban areas recorded a higher percentage of fogging spray related to dengue incidence (69.1%) followed by semiurban areas (69.1% and 40.5%; P < 0.001). Mosquito coils were highly used in rural areas (75.76%; P < 0.05), whereas mosquito coil utilization was more prevalent in semiurban areas than in urban areas (47.1% and 43.6%; P < 0.05). In contrast, a higher percentage of liquid vaporizers were used by urban respondents, followed by semiurban respondents, whereas a lower percentage of liquid vaporizer users were from rural areas (56.4%, 52.9%, and 24.2%, respectively; P < 0.05). There were no statistically significant differences among urban, semiurban, and rural households with recorded dengue cases within the previous 2 years and household insecticide consumption (P > 0.05; Table 2).
Table 2.
Urbanization level, dengue incidence, and mosquito control measures
| Variable | Rural (%) | Semiurban (%) | Urban (%) | |||
|---|---|---|---|---|---|---|
| Dengue cases recorded in the house within a year | ||||||
| Yes | 7 | (10.1) | 31 | (11.8) | 34 | (18.1) |
| No | 62 | (89.9) | 231 | (88.2) | 154 | (81.9) |
| P = 0.110 | ||||||
| Household income-level (rupees) | ||||||
| < 40,000 | 38 | (55.9) | 54 | (21.1) | 33 | (18.0) |
| 40,000–80,000 | 23 | (33.8) | 116 | (45.3) | 70 | (38.3) |
| > 80,000 | 7 | (10.3) | 86 | (33.6) | 80 | (43.7) |
| P = 0.000 | ||||||
| Application of fogging spray | ||||||
| Applied | 16 | (23.8) | 106 | (40.5) | 130 | (69.1) |
| Not applied | 53 | (76.2) | 156 | (59.5) | 58 | (30.9) |
| P = 0.000 | ||||||
| Using household insecticide | ||||||
| Consumers | 40 | (58.0) | 146 | (55.7) | 110 | (58.5) |
| Nonconsumers | 29 | (42.0) | 116 | (44.3) | 78 | (41.5) |
| P = 0.829 | ||||||
| Mode of application (household insecticide) | ||||||
| Mosquito coil | 25 | (75.8) | 66 | (47.1) | 41 | (43.6) |
| Liquid vaporizer | 8 | (24.2) | 74 | (52.9) | 53 | (56.4) |
| P = 0.004 | ||||||
Liquid vaporizers were used extensively by the high-income participants; comparing low- and middle-income households, utilization was more prevalent among middle-income households than low-income households (63.2%, 49.5%, and 29.7%, respectively; P < 0.001). However, mosquito coils were used by a greater percentage of low-income households than middle-income households, and a lower percentage of mosquito coils were used by high-income participants (70.3%, 50.0%, and 36.8%, respectively; P < 0.001). According to the χ2 likelihood, there was no statistically significant differences between the income level and dengue or household insecticide practices (P > 0.05; Table 3).
Table 3.
Household income level, dengue incidence, and household insecticide consumption
| Variable | Low income (%) | Middle income (%) | High income (%) | |||
|---|---|---|---|---|---|---|
| Dengue cases recorded in the house within a year | ||||||
| Yes | 15 | (12.0) | 30 | (14.4) | 25 | (14.5) |
| No | 110 | (88.0) | 179 | (85.6) | 148 | (85.5) |
| P = 0.791 | ||||||
| Using household insecticide | ||||||
| Consumers | 72 | (57.6) | 111 | (53.1) | 103 | (59.5) |
| Nonconsumers | 53 | (42.4) | 98 | (46.9) | 70 | (40.5) |
| P = 0.431 | ||||||
| Mode of application (household insecticide) | ||||||
| Liquid vaporizer | 19 | (29.7) | 51 | (49.5) | 60 | (63.2) |
| Mosquito coil | 45 | (70.3) | 50 | (50.5) | 35 | (36.8) |
| P = 0.000 | ||||||
Supplemental Table 4 shows the percentage of control measures taken by participating dengue recorded and nonrecorded households within the previous 2 years. Fogging spray was applied to a greater extent when dengue patients were recorded in households (65.3%; P < 0.05); there were statistical differences between household insecticide users or different modes of insecticide applications in households with a record of dengue (P > 0.05).
The highest education level of the head of the surveyed household and their likelihood differences with dengue incidence and household insecticide consumption were analyzed (Table 4). Mosquito coil use was more prevalent among the households with primary education as the highest education of the heads of the household, followed by diploma holders (82.4% and 57.9%, respectively; P < 0.05). Among participants where the head of household had a postgraduate degree, used mosquito coils was less common; they used liquid vaporizers to a greater extent than other education levels (30.0% and 70.0%, respectively; P < 0.05). Liquid vaporizers were rarely used by the households in which the heads had completely only primary education (17.6%; P < 0.05). There were no significant differences between education level and dengue incidence or household insecticides used (P > 0.05).
Table 4.
Head of household education level, dengue incidence, and household insecticide consumption
| Variable | Primary education (%) | Secondary education (%) | Diploma (%) | Graduate (%) | Postgraduate (%) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Was there a dengue patient in your family within the past 2 years? | ||||||||||
| Yes | 4 | (16.7) | 23 | (11.9) | 7 | (10.8) | 30 | (15.5) | 8 | (18.1) |
| No | 20 | (83.3) | 170 | (88.1) | 58 | (89.2) | 163 | (84.5) | 36 | (81.9) |
| P = 0.658 | ||||||||||
| Use of household insecticide | ||||||||||
| Consumers | 17 | (70.8) | 96 | (49.7) | 40 | (61.5) | 120 | (62.2) | 23 | (52.3) |
| Nonconsumers | 7 | (29.2) | 97 | (50.3) | 25 | (38.5) | 73 | (37.8) | 21 | (47.7) |
| P = 0.058 | ||||||||||
| Mode of application (household insecticide) | ||||||||||
| Liquid vaporizer | 3 | (17.6) | 44 | (49.4) | 16 | (42.1) | 58 | (56.3) | 14 | (70.0) |
| Mosquito coil | 14 | (82.4) | 45 | (50.6) | 22 | (57.9) | 45 | (43.7) | 6 | (30.0) |
| P = 0.009* | ||||||||||
In 2020, 900 kg of metofluthrin (5%), 510 kg of transfluthrin (99%), 9,000 kg of dimefluthrin (5%), 100 kg of cyphenothrin (93%), and 120 kg of imiprothrin (50%) were imported. Generally, w/w 0.01% strength metofulthin, w/v 0.90% strength transfluthrin, w/w 0.01% strength dimefulthin, w/w 0.175% strength cyphenothrin, and w/w 0.085% strength imiprothrin were commercially available as active ingredients in household insecticides. Therefore, in 2020 and/or 2021, 450,000 kg metofluthrin (w/w 0.01%), 56,100 kg transfluthrin (w/v 0.90%), 4,500,000 kg dimefluthrin (w/w 0.01%), 53,142.86 kg cyphenothrin (0.175%), and 70,588.24 kg imiprothrin (0.085%) were probably applied to the environment in the form of household insecticides (Supplemental Table 5).
DISCUSSION
The present community-based survey assessed participants’ knowledge and the influence of demographic factors on household insecticide use in dengue-endemic districts in Sri Lanka. The results of the present study reveal that income level, education level, and urbanization influenced household insecticide consumption, especially the preference for different formulations of insecticides. According to our findings, liquid vaporizers were the most widely used formulation compared with mosquito coils, but this was contrary to a survey report, conducted in northern Sri Lanka in 2007,20 in which the majority of the participants used mosquito coils. Given advancements in technology and development in the educated and industrial community, liquid vaporizers have replaced traditional methods of mosquito eradication and use of mosquito coils. Utilization preferences also varied according to the affordability of the product.21,22 According to the recent report of the Department of Census and Statistics,23 the percentage of poor households based on the official poverty line in 2016 was higher in rural areas (3.3%) than in urban areas (1.3%) of Sri Lanka. Preliminary survey results revealed that the cost per product is cheaper for mosquito coils than for electric liquid vaporizers. The results of the survey emphasized that mosquito coil use was prevalent in rural areas where per capita income was low and that liquid vaporizer use was higher in semiurban and urban areas where per capita income was comparably high.
Patterns of insecticide practice revealed peak utilization of household insecticides during the evening (from 3:00 pm–06:00 pm; 41.6%), followed by the whole night (starting at 6:00 pm; 24.3%). The abundance of mosquitoes during a particular period and getting a good night sleep without any disturbance or nuisance from mosquitos could be the primary reasons for this utilization pattern. However, Aedes sp. follows a diurnal feeding pattern, Culex sp. follows a nocturnal one, and Anopheles and Armigeres spp. commonly follow crepuscular behavior in feeding and host-seeking.24 Thus, household insecticide practices align with Aedes peak biting times (between 3:00 pm and 7:00 pm) in Sri Lanka.20 This finding also demonstrates the knowledge of mosquito-borne disease among the general public. As dengue has become an endemic disease in Sri Lanka with major epidemics arising yearly, the study population seems to be aware of Aedes mosquitoes and their biting times, whereas malaria and filaria are not included as frequently in the public awareness campaigns. In a study conducted in Colombo, only 49% of the respondents were aware of the biting behavior of dengue vectors.15 Hence, it is recommended to increase awareness of the general public about biting behavior and other bionomics of the vector mosquitoes through health education activities.
Daily use of mosquito coils and vaporizers targeting anthropophilic and indoor resting mosquitoes may lead to health problems among consumers, especially if they sleep in the vicinity of coils or vaporizers, which could lead to accumulation of the insecticides in an enclosed area, exposing users to the harmful effects of pollutants/particles from household insecticides, especially if they sleep in tightly closed rooms.21 Better ventilation mechanisms or sleeping under bed nets is advisable in such occasions. Thus, consumers should be made aware of alternative preventive measures to minimize the harmful effects of this practice. The majority of the participants used household insecticides daily (35.5%); comparable observations have been reported from Ghana,21 India,25 and Mexico.26 However, a study conducted in India27 reported that the majority of participants used mosquito repellents when the mosquito population was high, typically during or after the rainy season, and 32% of the participants of the present study also used household insecticides only during the high mosquito breeding seasons. Daily practice, even without the mosquito population, may also increase mosquitoes’ resistance to the insecticides, which could result in loss of product efficacy. Several findings from the present study regarding the use of household insecticides reveal that consumers should be properly informed about proper utilization.
The majority (62.8%) of participants were not aware of the chemicals used in household insecticides; some of the participants requested information regarding these chemicals and the side effects of long-term utilization in the comment section of the questionnaire. Among the customers who were aware of the chemicals used, some mentioned that they knew the chemicals might not be good for their health, but they had to use them as there were no other options for avoiding mosquitoes. Therefore, it is possible that the community assumes the use of household insecticide is sufficient to reduce mosquito populations, ignoring routine mosquito breeding site eradication practices.12 Hence, it is important to educate people regarding integrated vector management systems.
In Sri Lanka, space-spraying is mainly carried out in an area after a dengue case has been reported. For a single case of dengue fever, space spray is applied to cover an ∼200-m radius of the patient’s house or the source of infection.28 Interestingly, the current study recorded a higher percentage of dengue cases at sites where fogging was applied within the previous 2 years than in households with no dengue cases recording from January 2019 to March 2021. Space-spraying is primarily performed by health authorities of the country, but we found that 34.7% of the households recording cases of dengue fever had not received any application of fogging. Possible reasons could be unsatisfactory coordination between government entities and other stakeholders, outdated vector management strategies, and local political conflicts.15
The majority of customers of all three brands in this study had moderate and poor satisfaction with the effectiveness of the household insecticide products that they used. It was pointed out that effectiveness was not the main reason for selecting a particular brand. A similar observation was found in Ghana and it was mentioned that several factors mediated users’ choice of coils including the color of the coils.21 Nonusers used smoke from neem leaves, cinnamon leaves, coconut husks, and cashew shells, as well as mosquito bed nets, fans, mosquito shutter rackets, and citronella oils to control mosquitos. The reason for not using insecticides was mainly health issues such as allergies, headache, and wheezing; concern about health and the environment; and unpleasant smells from the mosquito coils.
Although this study reports on commercially available household insecticide practices to control mosquitoes in dengue-endemic areas, it is important to consider the country’s annual use of household insecticides. Because this is the first comprehensive work done in Sri Lanka regarding household insecticides to control mosquitoes, no relevant data were available. Therefore, the study used secondary data from the records maintained by the Office of Pesticide Registrar. In Sri Lanka, metofluthrin (w/w 0.01%) and dimefluthrin (w/w 0.01%) are available as active ingredients in mosquito coils, transfluthrin (w/v 0.9%) is used in vaporizers, and cyphenothrin (w/w 0.175%) and imiprothrin (w/w 0.0855) are used in aerosols. According to these records, in 2020, 5,129,831.1 kg of all the aforementioned five active ingredients of commercially available household insecticide products to control mosquitoes were imported to the island. Prallethrin (w/v 1.24% and w/v 1.26%) and d-trans-allethrin (w/w 0.12%) are also available in two vaporizer brands and a mosquito coil brand, respectively. Data for these were not available in the Office of Pesticide Registrar records because they are not imported as technical materials. Hence, it is not easy to determine which formulation is used most often in the country. It is recommended that a proper database system be established, mainly because these products have reached the environment, and their overuse could reduce the efficacy of the products by creating mosquito resistance.
Interestingly, more than half of the participants (57.0%) used household insecticides, whereas the remaining (43.0%) were nonconsumers, which was a strength of this study to achieve its objectives without bias. This study provides current data on commercial household insecticide use and the influence of demographic and socioeconomic factors in household insecticide consumption in dengue-endemic areas in Sri Lanka. The findings may increase our understanding of community knowledge and practices regarding household insecticides to control mosquitoes, which would help design sustainable integrated vector control strategies and lead to change and the adoption of new strategies. This study suggests that attitudes and practices regarding household insecticide use are not satisfactory. Therefore, there is a need for programs to raise awareness regarding chemicals included in household insecticides, the disadvantages of inappropriate use of these products, a better understanding of correct use, and the best alternative practices to reduce mosquito populations while using household insecticides simultaneously.
Supplemental Materials
ACKNOWLEDGMENTS
We thank the respondents for their valuable time in completing our survey and the Office of the Pesticide Registrar for providing the secondary data. The American Society of Tropical Medicine and Hygiene (ASTMH) assisted with publication expenses.
Note: Supplemental materials appear at www.ajtmh.org.
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