Household use of insecticide consumer products in a dengue-endemic area in México

Authors


Abstract

Objectives

To evaluate the household use of insecticide consumer products to kill mosquitoes and other insect pests, as well as the expenditures for using these products, in a dengue-endemic area of México.

Methods

A questionnaire was administered to 441 households in Mérida City and other communities in Yucatán to assess household use of insecticide consumer products.

Results

A total of 86.6% of surveyed households took action to kill insect pests with consumer products. The most commonly used product types were insecticide aerosol spray cans (73.6%), electric plug-in insecticide emitters (37.4%) and mosquito coils (28.3%). Mosquitoes were targeted by 89.7% of households using insecticide aerosol spray cans and >99% of households using electric plug-in insecticide emitters or mosquito coils. Products were used daily or every 2 days in most of the households for insecticide aerosol spray cans (61.4%), electric plug-in insecticide emitters (76.2%) and mosquito coils (82.1%). For all products used to kill insect pests, the median annual estimated expenditure per household that took action was 408 Mexican pesos ($MXN), which corresponded to approximately 31 $US. These numbers are suggestive of an annual market in excess of 75 million $MXN (>5.7 million $US) for Mérida City alone.

Conclusion

Mosquitoes threaten human health and are major nuisances in homes in the study area in México. Households were found to have taken vigorous action to kill mosquitoes and other insect pests and spent substantial amounts of money on insecticide consumer products.

Abstract

Objectifs

Evaluer l'utilisation des biens de consommation insecticides par les ménages pour tuer les moustiques et autres insectes nuisibles, ainsi que les dépenses pour l'utilisation de ces produits, dans une région du Mexique endémique pour la dengue.

Méthodes

Un questionnaire a été soumis à 441 ménages dans la ville de Mérida et d'autres communautés dans le Yucatan afin d’évaluer l'utilisation des biens de consommation insecticides par les ménages.

Résultats

86,6% des ménages ont pris des mesures pour tuer les insectes nuisibles avec des biens de consommation insecticides. Les types de produits les plus couramment utilisés sont des bombes pulvérisateurs d'aérosols insecticides (73.6%), des émetteurs électriques d'insecticides (37.4%) et des spiraux anti-moustiques (28.3%). Les moustiques ont été ciblés par 89.7% des ménages utilisant des insecticides en pulvérisateurs d'aérosols et > 99% des ménages utilisant des émetteurs électriques d'insecticides ou des spiraux anti-moustiques. Les produits ont été utilisés quotidiennement ou tous les 2 jours dans la plupart des ménages pour les bombes pulvérisateurs d'aérosols insecticides (61.4%), les émetteurs électriques d'insecticides (76.2%) et les spiraux anti-moustiques (82.1%). Pour tous les produits utilisés pour tuer les insectes nuisibles, la dépense annuelle moyenne estimée par ménage ayant pris des mesures était de 408 pesos mexicains ($ MXN), ce qui correspond à ~ 31 $ US. Ces chiffres sont évocateurs d'un marché annuel de plus de 75 millions $ MXN (> 5.7 millions $ US) pour la seule ville de Mérida.

Conclusion

Les moustiques menacent la santé humaine et constituent d'importantes nuisances dans les habitations dans la zone d’étude au Mexique. Les ménages sont amenés à prendre des mesures vigoureuses pour tuer les moustiques et autres insectes nuisibles et dépensent des sommes importantes d'argent pour des biens de consommation insecticides.

Abstract

Objetivos

Evaluar el uso de insecticidas domésticos en hogares para matar mosquitos y otras plagas de insectos, al igual que el gasto de utilizar estos productos, en un área de Méjico endémica para el dengue.

Métodos

Se administró un cuestionario a 441 hogares en la Ciudad de Mérida y otras comunidades del Yucatán para evaluar el uso insecticidas domésticos.

Resultados

Un 86.6% de los hogares realizaban acciones concretas para las matar plagas de insectos utilizando productos de uso doméstico. Los tipos de productos más comúnmente utilizados eran latas de insecticida en aerosol (73.6%), difusores eléctricos de insecticida (37.4%) y espirales para mosquitos (28.3%). Los mosquitos se contralaban en un 89.7% de los hogares utilizando insecticida en aerosol y en más del 99% de los hogares utilizando difusores eléctricos de insecticida o espirales para mosquitos. Los productos eran utilizados a diario o cada dos días en la mayoría de los hogares; insecticida en aerosol (61.4%), difusores eléctricos de insecticida (76.2%), y espirales para mosquitos (82.1%). El gasto medio anual calculado para todos los productos utilizados para matar plagas de insectos, por hogar que realizaba la acción, era de 408 pesos mejicanos ($MXN) lo que correspondía ~31 $U.S. Estos números sugieren un mercado anual en exceso de 75 millones $MXN (>5.7 millones $U.S.) solo para la ciudad de Mérida.

Conclusión

Los mosquitos amenazan la salud humana y son una molestia importante en los hogares del área de estudio en Méjico. Se encontró que los hogares tomaban medidas activas para matar los mosquitos y otras plagas de insectos y gastaban cantidades sustanciales de dinero en productos pesticidas de uso domésticos .

Introduction

In a previous study on the effectiveness of insecticide-treated window curtains to prevent entry into homes in Mérida City, Yucatán State, México, by the dengue virus (DENV) mosquito vector Aedes aegypti, we reported common household use of insecticide consumer products to kill mosquitoes: aerosol spray cans with insecticide were used to kill mosquitoes in approximately 70% of homes, and insecticide emitters were used in 10–20% of homes (Loroño-Pino et al. 2013). This heavy use of insecticide consumer products is not surprising in the light of our previous reports of large numbers of A. aegypti and another human-biting mosquito, Culex quinquefasciatus, being present in homes in Mérida City (García-Rejón et al. 2008; Loroño-Pino et al. 2013). Other studies have reported use of insecticide consumer products for 28–89% of households in dengue-endemic settings in Asia (van Benthem et al. 2002; Itrat et al. 2008; Syed et al. 2010; Naing et al. 2011; Al-Dubai et al. 2013; Mayxay et al. 2013) or the Americas (Shuaib et al. 2010). However, details are very scarce in these and our previous publication with regard to the extent of insecticide consumer product use – for example, how often and in which parts of the home they are used – and the amount of money spent on the products. This is unfortunate because, as shown by a recent study from a malaria-endemic area in Africa, much can be learned from in-depth assessments of household use of pest control products (Nalwanga & Ssempebwa 2011). Moreover, there are potential negative health effects, particularly for asthma and respiratory diseases, from inhalation of pesticide aerosols or vapours (Hernandez et al. 2011).

Improved knowledge of the extent of household use of insecticide consumer products is important not only to determine the willingness of households to invest in the use of domicile-targeted insecticide-based products – to kill mosquitoes, cockroaches and other indoor pests – but also to help assess the overall insecticide exposure in the environment stemming from household use, vector control programme applications to suppress mosquitoes or other arthropods spreading pathogens to humans or domestic animals, and agricultural applications to protect crops. Here, we report on a study aiming to generate detailed knowledge of household use of insecticide consumer products to kill mosquitoes and other common household insect pests, and the expenditures for using these products, in the dengue hyperendemic Yucatán State, México.

Methods

Study area and study population

The study was conducted in Yucatán State in southern México. This subtropical area is hyperendemic for dengue – with co-circulation of multiple DENV serotypes – with A. aegypti being the primary local mosquito vector for DENV (Loroño-Pino et al. 2004, 2013; García-Rejón et al. 2008, 2011). Study communities included Mérida City, which is the major urban centre in Yucatán State, two of this city's adjacent satellite communities (Caucel & Umán) and three more rural outlying communities (Hunucmá, Maxcanú and Motul) located 20–50 km from Mérida City (Figure 1). The grouping of Mérida City, Caucel and Umán is hereafter referred to as the urban area; the grouping of Hunucmá, Maxcanú and Motul is referred to as the rural area.

Figure 1.

Location of study communities in Yucatán State in southern México and of study neighbourhoods in the western and eastern parts of Mérida City (shaded areas).

Across these communities, we recruited clusters of households to participate in a study aiming to determine the protective effect of insecticide-treated window curtains against intrusion by A. aegypti in relation to the local insecticide resistance profile for this mosquito. Paired clusters of study homes were to receive insecticide-treated window curtains or similar but non-treated window curtains, respectively, in September 2012. The results reported here are based on a questionnaire administered in 441 households in July–August 2012 – before the homes received window curtains – to generate detailed baseline knowledge of household use of insecticide consumer products and the expenditures for their use. Of the 441 study households, 350 were located in the urban area (294 in Mérida City, 17 in Caucel and 39 in Umán) and 91 in the rural area (18 in Hunucmá, 36 in Maxcanú and 37 in Motul). Study households in Mérida City were spread across multiple neighbourhoods in the western and eastern parts of the city. The study participant answering the questionnaire on behalf of the household most commonly was female (87%). Approximately 62% of the respondents reported working in the home or being retired vs. 38% working or studying outside of the home. The vast majority of study homes were one-storey cement block buildings equipped with electricity and running water but lacking central air conditioning.

Study questionnaire

The questionnaires were administered (in Spanish) in person during home visits by professional anthropologists (co-authors Chan-Dzul and Zapata-Gil) or a professional nurse (co-author Carrillo-Solís) trained by the anthropologists in administering the questionnaire. The questionnaire content was informed by our previous study in Mérida City (Loroño-Pino et al. 2013) and through pre-study visits to households in the area by the anthropologists to gather preliminary information about actions taken to kill household insect pests. Administering the questionnaire typically took between 20 and 40 min, depending on the need to clarify questions to the respondents and the amount of information they shared. The full questionnaire is available as supplementary online material, in the original Spanish version and as an English translation.

The initial question was: Is anyone in the family doing something to kill insect pests (like mosquitoes, flies, cockroaches, ants or termites) either inside or outside the home (Yes or No)? If the answer was No, a single follow-up question determined the reason for not taking action. If the answer was Yes, the questions outlined below were pursued. A first set of questions focused on the following: the specific methods/product types used to control insect pests (insecticide aerosol spray can, electric plug-in insecticide emitter, mosquito coil, smoke, electric insect racquet, candle and/or other methods); the brand names and brand name varieties of the products used; and what type of pests for which a specific product type was used (mosquitoes, flies, cockroaches, ants, termites, scorpions and/or other pests).

To ensure that product types and brand varieties of consumer products were remembered correctly by the respondents, the householders were asked to show the products they used and also to pick them out from a product catalogue designed by the anthropologist/nurse team specifically for this purpose. This product catalogue showed colour images of 63 locally marketed products, including 35 brand varieties of insecticide aerosol spray cans, 15 brand varieties of electric plug-in insecticide emitters, 10 brand varieties of mosquito coils, one electric insect racquet and two types of candles.

A second set of questions focused on the following: when the products were used (year around, only during the rainy season, only when there are mosquitoes or other times); how frequently, as well as how many of, the products were purchased and used (every day, every 2 days, once a week, once every 15 days, once per month or other options); the approximate cost per item; and where the products were purchased (small store, supermarket, street salesperson and/or other options). Another question determined whether the householder followed the manufacturer's instructions for use of a given product (Yes, No or I don't know). Based on their additional verbal description of the product's use in the household, the anthropologist/nurse team then classified each product's use as correct or incorrect. Correct use of an insecticide aerosol spray can entailed the following: (i) closing windows and doors, covering food, and moving people and pets outdoors; (ii) shaking the spray can before applying the insecticide aerosol and then allowing 20 min before opening windows and doors and going back indoors; (iii) applying the insecticide aerosol directly over the insects to the extent possible; and (iv) applying the insecticide aerosol in corners and under or inside furniture, moving from the interior of the home to the exit door. Correct use of an electric plug-in insecticide emitter entailed using the product in a power outlet located close to a window or door that was open at least part of the time to encourage mosquitoes to leave the home. Correct use of a mosquito coil entailed burning it near an open door or window or in an open space such as a patio.

A third set of questions focused on the rooms of the home where the specific methods used to control insect pests were employed (living/dining room, kitchen, bedroom of children <18 years of age, bedroom of adults 18 years or older, bathroom, storage room, laundry room, other room type, all rooms in the home and/or patio/terrace), as well as the reason(s) for use of the product in those room types. Finally, we estimated the total expenditures per year for specific methods/product types to kill household insect pests, as well as for all methods/product types combined. These estimations were based on the answers given for each household for the frequency of purchasing specific products, the numbers of items purchased and the item cost. The estimated product-specific expenditures were then summed to obtain the total expenditure for a given method/product type (e.g. insecticide aerosol spray cans) and for all products combined in each household.

Data management and statistical analysis

Field-collected data were entered into a research electronic data capture (REDCap) database (Harris et al. 2009) and were exported to Microsoft Excel (Microsoft Corporation, Redmond, WA, USA) prior to data analysis. Statistical analyses were carried out using the JMP® statistical package (Sall et al. 2005), and results were considered significant when < 0.05. Differences in the percentage of households that engaged in a specific activity were compared statistically using the likelihood ratio chi-square test within contingency table analysis. Data on household expenditures for the use of insecticide consumer products were highly skewed and therefore were compared statistically using the Wilcoxon rank-sum test; application of the two-sample t-test to log transformation of these data produced statistically similar results (not shown).

Human subjects research approval

The study was approved by the Bioethics Committee of Centro de Investigaciones Regionales Dr. Hideyo Noguchi, Universidad Autónoma de Yucatán and the Institutional Review Board of Colorado State University.

Results

Percentage of households taking action to kill insect pests and methods used

For all 441 study households combined, 86.6% took action to kill insect pests – such as mosquitoes, flies, cockroaches, ants or termites – inside or outside the home (Table 1). The percentages of households taking such action were similar for the urban area and the rural area (85.7% and 90.1%, respectively) (Table 1). Among the 59 households not taking action to kill insect pests, the most prominent specific reasons given were that no mosquitoes were found inside the home (25), that residents had allergies (22) or that the home had window screens (9).

Table 1. Percentage of households taking action to kill household insect pests inside or outside the home, and the methods most commonly used by those taking action
 All study householdsUrban areaRural area
Number%Number%Number%
  1. The statistical significance for the observed differences between the urban area and the rural area are indicated as follows: NSP > 0.05; *< 0.05; **< 0.01; and ***< 0.001.

Action taken to kill household insect pests (e.g. mosquitoes, flies, cockroaches, ants or termites)
Number of households441 350 91 
Yes38286.630085.78290.1NS
No5913.45014.399.9NS
Methods used to control household insect pests (a household can report use of >1 method)
Number of households382 300 82 
Insecticide aerosol spray can28173.623879.34352.4***
Electric plug-in insecticide emitter14337.49933.04453.7***
Mosquito coil10828.38227.32631.7NS
Smoke195.0155.044.9NS
Electric insect racquet112.9103.311.2NS

For the 382 households that took action to kill household insect pests, the most commonly used method was insecticide aerosol spray cans (73.6%), followed by electric plug-in insecticide emitters (37.4%) and mosquito coils (28.3%) (Table 1). Other methods reported less frequently included burning various items (e.g. egg cartons, herbs or wood) to produce smoke, use of electric insect racquets or citronella candles, or physically killing mosquitoes by hitting them with various objects. Insecticide aerosol spray cans were used by a greater percentage of households in the urban area as compared with the rural area (79.3% and 52.4%; < 0.001), whereas use of electric plug-in insecticide emitters was more prevalent in the rural area than in the urban area (53.7% and 33.0%; < 0.001) (Table 1). The use of mosquito coils was similar between the community groupings.

With regards to the household insect pest for which a specific type of product was used, mosquitoes were named by 89.7% of 281 households using insecticide aerosol spray cans, 99.3% of 143 households using electric plug-in insecticide emitters and all households using mosquito coils, smoke or electric insect racquets. Insecticide aerosol spray cans were used extensively against mosquitoes by households in the urban area (89.1%), as well as in the rural area (93.0%). They also were used against other household insect pests, including cockroaches (73.3% of households using insecticide aerosol spray cans), ants (36.7%) and flies (29.2%). Percentages of households using insecticide aerosol spray cans against specific pests were similar (> 0.05) between the urban and rural households.

Based on the assessment by the anthropologist/nurse team of the descriptions given by respondents for how they employed a given product type, the use was classified as correct for 88.9% for insecticide aerosol spray cans, compared with 64.9% for mosquito coils, and only 42.3% for electric plug-in insecticide emitters.

Timing of actions to kill household insect pests for the most commonly used methods

Of the households that used a specific method, 69.5% reported using insecticide aerosol spray cans year around, 46.3% reported using electric plug-in insecticide emitters year around and 47.6% reported using mosquito coils year around (Table 2). The remaining households used these products only seasonally (during the rainy season) or sporadically (when mosquitoes or other insect pests were seen). Year-round use of insecticide aerosol spray cans was reported by 71.1% of households in the urban area and 60.0% of households in the rural area (Table 2). Corresponding year-round use of electric plug-in insecticide emitters or mosquito coils was reported for 44.0% and 46.8%, respectively, of households in the urban area vs. 51.2% and 50.0%, respectively, of households in the rural area (Table 2). There were no statistically significant differences between urban and rural households in the likelihood of using insecticide aerosol spray cans, electric plug-in insecticide emitters or mosquito coils year around vs. only during parts of the year (P > 0.05).

Table 2. Timing of actions to kill household insect pests for the most commonly used methods
 All responding study householdsUrban areaRural area
Number%Number%Number%
  1. The statistical significance for the observed differences between the urban area and the rural area are indicated for use year around vs. only seasonally (noted with the percentage value for year around use) as follows: NSP > 0.05; *< 0.05; **< 0.01; and ***< 0.001.

Part(s) of the year when insecticide aerosol spray cans were used
Number of households272 232 40 
Only during the rainy season4014.72812.11230.0
Only when there are mosquitoes4315.83916.8410.0
Year around18969.516571.12460.0NS
Frequency of use of insecticide aerosol spray cans
Number of households277 235 42 
Daily7226.06025.51228.6
Every 2 days9835.47933.61945.2
Once per week6824.55925.1921.4
Less often than weekly3914.13715.724.8
Part(s) of the year when electric plug-in insecticide emitters were used
Number of households134 91 43 
Only during the rainy season3929.12426.41534.9
Only when there are mosquitoes3324.62729.7613.9
Year around6246.34044.02251.2NS
Frequency of use of electric plug-in insecticide emitters
Number of households139 95 44 
Daily5741.03132.62659.1
Every 2 days4935.33637.91329.6
Once per week1712.21313.749.1
Less often than weekly1611.51515.812.3
Part(s) of the year when mosquito coils were used
Number of households105 79 26 
Only during the rainy season3331.42126.61246.2
Only when there are mosquitoes2221.02126.613.9
Year around5047.63746.81350.0NS
Frequency of use of mosquito coils
Number of households106 80 26 
Daily4744.33138.81661.5
Every 2 days4037.73543.8519.2
Once per week1312.3810.0519.2
Less often than weekly65.767.500.0

When a given method was used, the reported frequency of use for all study homes combined was either daily or every 2 days in 61.4% of households for insecticide aerosol spray cans, 76.3% of households for electric plug-in insecticide emitters and 82.1% of households for mosquito coils (Table 2). The corresponding percentages for use either daily or every 2 days in households in the urban area or the rural area were 59.1% and 73.8%, respectively, for insecticide aerosol spray cans, 70.5% and 88.6%, respectively, for electric plug-in insecticide emitters, and 82.5% and 80.8%, respectively, for mosquito coils (Table 2). Use of electric plug-in insecticide emitters either daily or every 2 days was more prevalent in the rural area than in the urban area (= 0.014), whereas there were no statistically significant differences between the urban and rural areas for the other methods.

Intradomicile and outdoor patio use patterns for the most commonly employed methods to kill household insect pests

The pattern of intradomicile and outdoor patio use of insecticides varied by method, as well as between urban and rural households. For all study households combined, insecticide aerosol spray cans were used most commonly in bedrooms (88.6%) but were also used extensively in bathrooms (74.4%), living/dining rooms (69.8%) and kitchens (61.9%) (Table 3). Use of insecticide aerosol spray cans in the outdoor patio was sporadic (6.0%). Electric plug-in insecticide emitters were used commonly in bedrooms (81.1% of households), to a lesser extent in living/dining rooms (44.8%), only rarely in kitchens or bathrooms (<15%), and not in the outdoor patio (Table 3). Mosquito coils were used commonly in living/dining rooms (68.5% of households) and bedrooms (49.1%), but less frequently in kitchens (31.5%), bathrooms (15.7%) or outdoor patios (13.0%) (Table 3).

Table 3. Use of the most commonly employed methods to kill household insect pests in selected room types and the outdoor patio
 All responding study householdsUrban areaRural area
Number%Number%Number%
  1. The statistical significance for the observed differences between the urban area and the rural area are indicated as follows: NSP > 0.05; *< 0.05; **< 0.01; and ***< 0.001.

Parts of the home where insecticide aerosol spray cans were used (a household can report >1 room type)
Number of households281 238 43 
Bedroom24988.621088.23990.7NS
Living/dining room19669.816067.23683.7*
Kitchen17461.913958.43581.4**
Bathroom19074.415866.43274.4NS
Outdoor patio176.0177.100.0*
Parts of the home where electric plug-in insecticide emitters were used (a household can report >1 room type)
Number of households143 99 44 
Bedroom11681.18585.93170.5*
Living/dining room6444.84040.42454.5NS
Kitchen2114.777.11431.8***
Bathroom1510.566.1920.5*
Outdoor patio00.000.000.0
Parts of the home where mosquito coils were used (a household can report >1 room type)
Number of households108 82 26 
Bedroom5349.13846.31557.7NS
Living/dining room7468.55668.31869.2NS
Kitchen3431.52328.01142.3NS
Bathroom1715.7911.0830.8*
Outdoor patio1413.01214.627.7NS

The likelihood of insecticide aerosol spray cans being used in a given room type in households was similar in the urban and rural area households for bedrooms and bathrooms ( 0.292) but was higher in the rural area for living/dining rooms (= 0.023) and kitchens (= 0.003) (Table 3). The likelihood of electric plug-in insecticide emitters being used in a given room type in households in the urban area was similar to that in rural area households for living/dining rooms (= 0.117) and was higher in the urban area for bedrooms (= 0.035), but was higher in the rural area for kitchens and bathrooms ( 0.013). The likelihood of mosquito coils being used in a given room type in households was similar in the urban and rural areas for bedrooms, living/dining rooms and kitchens ( 0.180) but was higher in the rural area for bathrooms (= 0.023). For outdoor patios, households in the urban area were more likely to use insecticide aerosol spray cans than rural area households (= 0.016), whereas the likelihood of using mosquito coils was similar between urban and rural households (= 0.335).

Expenditures for actions to kill household insect pests

For all methods used to kill household insect pests combined, the median annual estimated expenditure per household that took action was 408 Mexican pesos ($MXN) (Table 4). Using a conversion rate of 1 $US to 13.30 $MXN for July 2012 when the survey was undertaken, this corresponded to approximately 31 $US. The median annual expenditure per household was significantly (= 0.028) higher in the rural area (453 $MXN) than in the urban area (384 $MXN) (Table 4). For all households combined, 69.4% were estimated to spend >200 $MXN (>15 $US) per year on products to kill insect pests, 39.0% were estimated to spend >500 $MXN (>37 $US) per year and 17.5% were estimated to spend >1000 $MXN (>75 $US) per year (Table 4). The likelihood of households spending >200 $MXN or >500 $MXN per year on products to kill insect pests was similar between the community groupings, whereas a significantly (= 0.036) higher percentage of households in the rural area reported spending >1000 $MXN per year. In Table 4, we also present similar summary statistics on annual expenditure for insecticide aerosol spray cans, electric plug-in insecticide emitters or mosquito coils separately.

Table 4. Estimated annual expenditures for methods to kill household insect pests
 All responding study householdsUrban areaRural area
  1. The statistical significance for the observed differences between the urban area and the rural area are indicated as follows: NSP > 0.05; *< 0.05; **< 0.01; and ***< 0.001.

Approximate annual expenditure ($MXN) for all methods combined in households taking action to kill household insect pests
Number of households38230082
Median expenditure408384453*
Range for expenditure<10–6173<10–617310–4514
% of households spending >200 $MXN69.468.074.4NS
% of households spending >500 $MXN39.037.345.1NS
% of households spending >1000 $MXN17.515.325.6*
Approximate annual expenditure ($MXN) for use of insecticide aerosol spray cans in households using that method
Number of households28123843
Median expenditure336324420NS
Range for expenditure30–364030–240030–3640
% of households spending >200 $MXN66.265.172.1NS
% of households spending >500 $MXN29.529.032.6NS
% of households spending >1000 $MXN7.57.19.3NS
Approximate annual expenditure ($MXN) for use of electric plug-in insecticide emitters in households using that method
Number of households1439944
Median expenditure270180584***
Range for expenditure<10–3650<10–1,80010–3650
% of households spending >200 $MXN55.247.572.7**
% of households spending >500 $MXN35.728.352.3**
% of households spending >1000 $MXN16.813.125.0NS
Approximate annual expenditure ($MXN) for use of mosquito coils in households using that method
Number of households1088226
Median expenditure135118140NS
Range for expenditure<10–5011<10–501124–1460
% of households spending >200 $MXN36.134.142.3NS
% of households spending >500 $MXN12.012.211.5NS
% of households spending >1000 $MXN6.56.17.7NS

Discussion

Our most important findings were that the vast majority (87%) of households in a dengue-endemic area in México take vigorous action to kill mosquitoes and other household insect pests and that a substantial amount of money (median annual estimated expenditure per household of 408 $MXN) was spent on insecticide consumer products to control nuisance insects and pathogen vectors. Our data indicate that the market for insecticide consumer products is substantial both in urban and rural settings in dengue-endemic areas in México. For example, Mérida City alone includes approximately 230 000 households (based on data for 2010 from Instituto Nacional de Estadística y Geografía). Based on a median annual estimated expenditure per household that takes action to kill insect pests in this urban area of 384 $MXN, and with 86% of all households taking action, the annual market for insecticide consumer products exceeds 75 million $MXN (>5.7 million $US) in Mérida City alone. To the best of our knowledge, this is the first study to provide a detailed description of household insecticide consumer product use in a dengue-endemic setting and to estimate the household expenditure for these products. The main weakness of the study is the usual problem in any retrospective survey – that is, recalling actions taken over a long time period (1 year). To minimise recall bias, the questionnaires were administered in person during home visits. This practice allowed for clarification of questions that were confusing to some of the respondents, as well as for the individuals administering the questionnaire to aid the respondents in recalling their actions as accurately as possible.

The extensive use of household insecticide consumer products in the study area likely is related, in large part, to heavy infestation of homes by human-biting mosquitoes, most notably the DENV vector A. aegypti and the nuisance-biter C. quinquefasciatus. During the rainy season, single households can harbour very large numbers – sometimes >100 – of these mosquitoes (García-Rejón et al. 2008; Loroño-Pino et al. 2013). Our main findings likely are relevant across much of the American subtropics and tropics where socioeconomic conditions are comparable to México. As a case in point, a study from the dengue-endemic island of Jamaica in the Caribbean reported use of insecticide sprays by 62% of households, without giving further details of use or cost (Shuaib et al. 2010). In our study area, mosquitoes were the most important targets for use of insecticide aerosol spray cans, as well as electric plug-in insecticide emitters and mosquito coils. Insecticide aerosol spray cans also were used commonly to kill cockroaches, ants and flies. Occasionally reported non-standard use of the products included splitting mosquito coils into multiple pieces to be burned in different rooms, using individual electric plug-in insecticide emitters longer than recommended, or burning the portion of the emitter containing the insecticide after it had been used.

Year-round use of insecticide consumer products to kill mosquitoes by many people, most often with applications daily or every 2 days, as observed in this study (Table 2), is consistent with our previous findings that mosquitoes infest homes in the study area year around (García-Rejón et al. 2008; Loroño-Pino et al. 2013). Likewise, the extensive use of insecticide consumer products, particularly insecticide aerosol spray cans and electric plug-in insecticide emitters, in bedrooms (Table 3) is consistent with our previous studies showing that this room type is where most of the mosquitoes are found (García-Rejón et al. 2008; Loroño-Pino et al. 2013). The percentages of households taking action to kill household insect pests were high (>85%) in both the urban area and the rural area, and most households in both settings used insecticide consumer products year around and with high frequency. However, we found some notable differences between the urban and rural areas. Households in the urban area were more than twice as likely to use insecticide aerosol spray cans compared with electric plug-in insecticide emitters, whereas the extent of use was similar for these product types in the rural area (Table 1). These different use patterns could result from variable access to products in the urban and rural areas or to difference in cost per product item. We also found that the intensity of use and expenditures for insecticide consumer products were greater in the rural area (Table 4). Despite being used in a lower percentage of households (Table 1), the median annual estimated expenditure for use of insecticide aerosol spray cans per household (Table 4) was greater in the rural area than in the urban area (420 and 324 $MXN, respectively). Moreover, the median expenditure per household for electric plug-in insecticide emitters was more than twice as high in the rural area than in the urban area (584 and 180 $MXN, respectively). The most likely explanation for the more intensive use of insecticide consumer products in the rural area – with very high percentages (>95%) of households using insecticide consumer products at least weekly (Table 2) and application often including most room types (Table 3) – is that household insect pests are more prevalent and abundant in the rural area compared with the urban setting.

One important but poorly understood issue is to what extent household use of insecticide consumer products may contribute to build-up of insecticide resistance in local mosquito populations. Although our study cannot answer this question, we nevertheless documented extensive household use of specific products (brand varieties) containing pyrethroid insecticides in insecticide aerosol spray cans (allethrin, cyfluthrin, cypermethrin, cyphenothrin, imiprothrin, permethrin, prallethrin, tetramethrin and/or transfluthrin), electric plug-in insecticide emitters (allethrin) and mosquito coils (allethrin or transfluthrin). Of 25 total products reported to be used commonly (by ≥10 households) in the study area, only one brand variety of insecticide aerosol spray can contained a non-pyrethroid insecticide, the carbamate propoxur (in combination with the pyrethroid cyfluthrin). Four other rarely used (by ≤5 households) brand varieties of insecticide aerosol spray cans also contained propoxur in combination with pyrethroids or with a pyrethroid and the organophosphate dichlorvos. The nearly exclusive use of pyrethroid insecticides in household consumer products is problematic because we previously demonstrated that A. aegypti from Mérida City have become strongly knock-down resistant to pyrethroid insecticides (Ponce-García et al. 2009; Loroño-Pino et al. 2013). We therefore speculate that use of available insecticide consumer products in Mérida City has limited effectiveness to kill the DENV vector A. aegypti. Research is urgently needed to address this important issue.

Acknowledgements

We thank Moisés Novelo-Canto and Dora Camas-Tec of Universidad Autónoma de Yucatán for assistance with the study and the surveyed households for participating. The study was supported by the United States National Institutes of Health/National Institute of Allergy and Infectious Diseases (International Collaborations in Infectious Disease Research Program U01-AI-088647). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIAID or NIH.

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