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DENGUE KNOWLEDGE AND PRACTICES AND THEIR IMPACT ON AEDES AEGYPTI POPULATIONS IN KAMPHAENG PHET, THAILAND

ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
A knowledge, attitude, and practice (KAP) survey and an extensive entomologic survey were conducted in two sub-districts of Kamphaeng Phet province, Thailand, to test the hypothesis that correct dengue knowledge and practice reduce dengue vector populations. We found a negative association between respondents’ knowledge of preventive measures and the number of unprotected containers in and around their houses. Knowledge of development sites was positively associated with unprotected containers. No relationships existed between knowledge of dengue and adult mosquito reduction practices. A higher number of unprotected containers increased the likelihood of the house being infested with one or more adult Aedes aegypti. Surprisingly, houses of respondents that used mosquito coils or had screening on doors and windows were significantly more likely to be infested (odds ratio =2.0) with adult Ae. aegypti. We conclude that there is a direct link between knowledge on dengue prevention and container protection practices, whereas measures against adult mosquitoes are used only when people experience a mosquito nuisance problem.

INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Since the first major outbreak of dengue hemorrhagic fever (DHF) in Thailand in 1958, dengue has remained a serious health problem in this country, with epidemics occurring every three to five years.^1–3 The principal vector throughout tropical and sub-tropical areas is the mosquito Aedes aegypti (L.). Females of this species deposit their eggs in a variety of water-holding containers, such as jars used for domestic water storage, tires, and disposed items that have filled with rain water. Because an effective vaccine is not yet available, dengue control is limited to reduction of the vector population.⁴ This can be achieved by making water-holding containers unavailable for immature development (source reduction), by killing adult mosquitoes with insecticides, or by interfering with mosquito-human contact.

Dengue vector control requires effective participation of the local community.⁵ Although education campaigns have increased people’s awareness of dengue, it remains unclear to what extent this knowledge is put into practice, and to what extent this practice actually reduces mosquito populations. Knowledge, attitude, and practice (KAP) surveys provide a suitable format to evaluate existing programs and to identify effective strategies for behavior change. Thus far, such studies have been relatively rare in dengue research.⁶ Dengue KAP studies have primarily been used to evaluate the impact of health education and community-based programs.^7–11 Other KAP studies have been more descriptive,^12–16 and a few have attempted to find statistically significant determinants of knowledge and practices¹⁷ or their effect on vector populations.^18,19 Most of these studies do not include biologic and socioeconomic determinants in one comprehensive model, making relationships harder to detect and explain.

For the present cross-sectional study, we used a stepwise approach (Figure 1) in which the following research questions were addressed: 1) can differences in people’s knowledge of dengue be explained by their demographic background, 2) do knowledge of Ae. aegypti, dengue symptoms, and/or preventive measures contribute to better preventive practices, and 3) do these practices have a positive impact on immature and adult populations of Ae. aegypti? Our KAP study was carried out as part of a larger prospective study that is designed to examine entomologic risk for human infection with dengue virus. We present the results of our KAP study and the impact on vector populations of people at risk of infection.

View larger version (18K): [in this window] [in a new window]       FIGURE 1. Diagram of relationships between demographics, dengue knowledge, practices, and Aedes aegypti populations.

MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

All studied households were part of a larger epidemiologic study that encompassed more than 4,000 households from 19 villages in four sub-districts. A geographic information system, which was developed for our study area, was used to select 611 households for the present study. Each sub-district was represented by two villages or a part thereof.

Study design. A KAP questionnaire was designed to collect data on demographic characteristics, people’s knowledge of dengue, and people’s practices in managing water-holding containers and reducing mosquitoes in their house. To test the general hypothesis that correct dengue knowledge and practice reduce dengue vector populations, the results from the KAP survey were coupled with the results from an extensive entomologic survey during September and October 2004.

KAP survey The KAP survey was carried out between July 15 and October 6, 2004. Before the start of the study, permission was obtained from the head of the local public health office, the village chief, the Thai Ministry of Health (reference # 53/2546), and the University of California at Davis Institutional Review Board (Human Subjects Protocol Number 200311410–3). Informed consent was obtained from all human adult participants before the questionnaire was addressed. The questionnaire was evaluated before the beginning of the actual survey. Two teams of three persons conducted interviews. Each team consisted of a trained interviewer, a local public health volunteer, and one of the first two authors (CJMK or WT). The female head of household was preferably interviewed, but if she was absent, another adult resident was interviewed. A maximum of two attempts to interview the head of household was made during the daytime (between 8:00 AM and 11:00 AM). If that failed, a final attempt was made later in the day (between 5:00 PM and 8:00 PM). A person in 511 of the 611 selected households was interviewed. Two persons refused to participate, approximately half of the non-interviewed houses were unoccupied at the time of visit, and the remainder could not be found at home on all three attempts.

Knowledge of dengue was measured by asking questions related to disease symptoms, the vector, and preventive measures. In addition, questions were asked about the use of preventive measures against adult mosquitoes. Questions concerning knowledge and attitude were open questions and asked before the questions related to preventive measures.

Entomologic surveys. Between September 10 and November 4, 2004, the interviewed households were surveyed for the presence of larvae, pupae, and adults of Ae. aegypti as described in detail by Morrison and others.²² Briefly, seven two-person teams inspected the households between 8:00 AM and 12:30 PM. Two teams were responsible for adult collections, the remaining five teams for immature collections. Each team consisted of one staff member of the United States Armed Forces Research Institute of Medical Sciences Entomology Laboratory in Kamphaeng Phet and one collector was recruited from the village. As a result of residents being absent on at least 3 visits, we collected entomologic data from 492 households that were included in the KAP study.

Larval and pupal survey. All water-holding containers on the plot of a household were inspected for larvae or pupae and described on entomologic survey forms. If pupae were encountered, all pupae were taken. If only larvae were encountered, a sample of these larvae was taken. Recorded container variables included cover status (with/without), Abate ® status (with/without), and fish status (with/without). Immature surveys lasted an average of 42 minutes per household. The duration of collection depended on the number of water-holding containers found on each housing plot (range =10–187 minutes). In the laboratory, samples were crosschecked with the survey forms. Emerged mosquitoes from these samples were killed by freezing and identified as Ae. aegypti,Ae. albopictus, Culex spp., or Toxorhynchites spp.. Their numbers were recorded by the individual container, sex, and species. At least one larva or pupa was identified from 95% of the samples that were positive for immature mosquitoes.

Adult survey. Adult mosquitoes were collected with battery-powered backpack aspirators (John W. Hock Company, Gainesville, FL).²³ Collections were made from all indoor rooms, if permitted. Outdoor collections were made in separate collection cups from walls and objects located within three meters of the edge of the roof, but not from vegetation. For houses elevated on poles (50.3% of the houses), the outdoor area included the area underneath the house. Collections were also made from the toilet area. Adult surveys lasted an average of 13 minutes per household, but the duration of collection depended on size and complexity of the house (range = 6–39 minutes).

In the laboratory, adult mosquitoes were killed and identified as Ae. aegypti, Ae. albopictus, Culex spp., Armigeres spp., or Anopheles spp.. Their numbers were recorded on entomologic survey forms by individual household, location (indoor/outdoor/toilet), and mosquito sex.

Data management. Entomologic and KAP data were entered twice in Microsoft Office Access 2003 (Microsoft Corporation, Redmond, WA). The two databases were then synchronized and cleaned by checking empty cells, extreme values, and variables with inconsistent data when compared with related variables.

Knowledge of symptoms was defined as the respondent mentioning at least one of the following symptoms: fever, headache, nausea/vomiting, rash, bleeding, shock, or muscular pain.²⁴ A person had knowledge of Ae. aegypti development sites if he or she could identify at least one of the following main container types in Thailand: water storage jars, cement baths, ant traps, tires, flower pots/vases, and garbage. Similarly, we assumed that a person had knowledge of preventive measures if he or she mentioned at least one of the following measures: adding Abate ® (temephos) (American Cyanamid, Parsippany, NJ) changing stored water, using a mosquito net, turning containers upside down, insecticide spraying, using mosquito coils, covering containers, disposing of garbage, and placing fish in stored water. Overall knowledge of dengue was defined as the sum of knowledge of symptoms, knowledge of Ae. aegypti development sites, and knowledge of preventive measures. Each respondent obtained a score between 0 and 3.

Practices to prevent transmission of dengue were divided into two strategies: container protection and reduction of mosquito populations. Container protection was evaluated at both the container and the household level. At the household level variables of interest were the absolute number of containers that was not physically protected by a cover, chemically protected by Abate ® or biologically protected by fish and the proportion of protected containers. Mosquito reduction practice was defined as using at least one of the following measures to reduce human-mosquito contact and/or the numbers of adult mosquitoes: repellent, bed net or mosquito coils during the day, and screening on windows/doors.

Statistical analysis. For analysis of the relationships between demographic background, knowledge, practice, and mosquito populations, we used binary logistic and ordinal regression procedures, as well as the general linear model (SPSS version 12.0; SPSS Inc., Chicago, IL). Factors having a screening significance of P < 0.25 in univariate analysis were included in multivariate analysis. This analysis also included all possible two-way interactions in the full model. The final model was selected using a backward procedure. In the first step, all two-way interactions were excluded from the model. If there was no significant loss of fit as evaluated by comparing -2 log likelihoods in binary and ordinal regression (chi square distribution) or by comparing error variance in the general linear model approach (F distribution), the next step was to exclude the least significant factor until the model lost significant information compared with the previous model.

RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
KAP survey. Table 1 shows the demographic characteristics of the 511 respondents by sub-district. Because we intended to interview the female head of household, 82% of the respondents were women. The age of the respondents ranged between 15 and 82 years, of which 71% were between 30 and 60 years of age. There were no significant differences in sex and age distribution between the two sub-districts. Respondents from Na Bo Kham had more formal education than those from Kon Tee (P = 0.004). Overall, 10% of the respondents were unschooled, almost 60% of them had education levels of primary school grade four or less, and the remainder had received secondary schooling. Older persons received less education than younger ones (P < 0.001). Most of the respondents were farmers (65%), small tradesmen (14%), or unemployed (8%). However, in Na Bo Kham more respondents were farmers compared with those in Kon Tee (86% versus 44%). In latter sub-district, more persons made a living as small tradesmen or were unemployed.

Determinants of knowledge are shown in Figure 2. Sub-district, sex, age, and education were significantly related with overall knowledge of dengue in both univariate and multivariate analysis (Table 3). Persons living in Kon Tee had significantly lower knowledge of dengue than those in Na Bo Kham and females were more knowledgeable than males. Younger persons had more knowledge than older ones and people with more formal education knew more about dengue than persons with less schooling.

View larger version (15K): [in this window] [in a new window]       FIGURE 2. Determinants of dengue knowledge in Kamphaeng Phet Province, Thailand. P values are based on univariate ordinal regression and demonstrate the overall significance of differences in knowledge scores between the categories of each determinant.

Covers were the most frequently encountered protection (27% of all containers), followed by containers with Abate ®(13%) and fish (5%) (Table 5). Containers that were protected by Abate ®, a cover, or fish were much more likely to be free of Ae. aegypti pupae (odds ratio [OR] = 4.51, P < 0.001). Nevertheless, 1.8% of the protected containers were infested with pupae.

View larger version (16K): [in this window] [in a new window]       FIGURE 3. A, Likelihood of adult Aedes aegypti infestation in relation to the number of unprotected containers (solid line) with 95% confidence limits (dashed lines). B, Likelihood of adult Ae. aegypti infestation in relation to the proportion of protected containers (solid line) with 95% confidence limits (dashed lines).

DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Compared with studies in other parts of Thailand, knowledge of dengue disease symptoms was slightly lower. Especially the dengue specific symptoms of bleeding/rash, which were mentioned by only 29% compared with 77% in Chiang Mai Province¹⁷ and 48% in Mae Sot.¹⁵ This could indicate that people are not always able to distinguish dengue infection from other diseases. Knowledge of Ae. aegypti development sites was comparable to¹⁷ or slightly higher¹⁵ than in other Thai studies. Interestingly, in our study coconut shells were mentioned by roughly half of the respondents as important source for mosquito breeding, whereas they only accounted for 0.2% of breeding containers in the entomologic survey. This may be explained by the fact that coconut shells received relatively much attention in recent education campaigns in Kamphaeng Phet Province. Knowledge of measures to prevent dengue was similar compared with the other Thai studies.^17,26

Previous studies have reported conflicting results regarding the effects of knowledge on dengue prevention practices. Some studies have shown that dengue knowledge was associated with an increased use of preventive measures against the disease^15,17 and a reduced number of development sites for vector larvae.²⁷ Other studies found a significant reduction in the Ae. aegypti infestation index after community-based prevention campaigns.^8,11,28,29 Consistent with our results, however, were studies in Puerto Rico,⁹ Brazil,¹⁸ and Trinidad en Tobago¹⁹ that found little or no correlation between knowledge of dengue and levels of Ae. aegypti abundance as measured by larval surveys.

Previous investigators measured knowledge of dengue in various ways. Some determine knowledge of dengue by knowledge of the disease,^7,12,17 whereas others included knowledge of the vector and control measures.^{8,10,11,18,19} A few investigators used a score to measure overall dengue knowledge.^9,30 We used both methods in our study. An overall dengue knowledge score was calculated to use as an independent variable in ordinal regression and as a dependent variable in our linear models. Knowledge of symptoms, development sites, and preventive measures were included as independent variables in our statistical analyses. In this way, we obtained a robust picture of the various relations between knowledge, practices, and vector populations.

There were two unexpected results in our study. First, persons with knowledge of Ae. aegypti development sites had more potential development sites in and around their homes compared with persons without such knowledge. An explanation could be that people become more knowledgeable of mosquito development sites when they have a lot of them in and around their houses. Second, use of mosquito coils and the presence of screening on doors and windows were associated with a higher risk for houses being infested with adult Ae. aegypti. We reasoned that the result for screening could have been confounded with socioeconomic background: well-off families may own larger houses and may be more likely to invest in screening. The likelihood of collecting at least one Ae. aegypti may simply be higher in larger houses. We did find that larger houses were more likely to have screening (P=0.025) and when we controlled for house size, we still found a significant effect of screening. Perhaps families that have many Aedes mosquitoes in their house are more bothered by these and, therefore, more likely to invest in anti-mosquito measures. Apparently, these kinds of protective measures have no measurable impact because the number of mosquitoes was not reduced. The fact that results were similar for both mosquito coils and screening supports this notion. Future studies will need to verify if mosquito prevention measures were used thoroughly and effectively.

In accordance with World Health Organization recommendations, the Thai government launched a National Dengue Prevention and Control Plan (H.M. The King’s Project) in 1999. Through an Aedes larvae abatement program and a public education campaign, its main aims were to reduce case fatality rates below 0.2%, reduce dengue incidence below 50 cases per 100,000 population, and to reduce Aedes development containers to less than 50 per 100 houses.³¹ The public education campaign may have been the main reason for the high dengue awareness in our area. However, our entomologic survey demonstrated that vector densities were well above the defined target, especially for Kon Tee sub-district. Apparently, the program was successful in increasing people’s awareness of dengue, but it did not result in practices that led to the desired entomologic targets.

Our results indicate a weak relation between dengue knowledge and practice. Better knowledge does not necessarily lead to better practice, presumably because it is difficult to change a person’s behavior. In addition, better practice may not necessarily lead to a reduction of dengue risk because specific, dynamic targets for reduction of Ae. aegypti populations that will result in desired public health outcomes have not been defined and it is expected that they will be difficult to obtain.³² These issues must be addressed before community-based integrated Ae. aegypti control will provide effective prevention and control of epidemic DF/DHF. Vertically structured approaches have a well documented history of achieving immediate results in dengue control, but require the necessary infrastructure and resources to be sustainable.

Knowledge of preventive measures in our study improved practices by reducing the numbers of unprotected containers, whereas knowledge of dengue symptoms and development sites had no effect and opposite effect, respectively, on unprotected containers. This suggests that more emphasis should be put on practical ways to prevent dengue in educational campaigns, especially on how to get rid of development sites. Although it was not directly associated with better practice, knowledge of symptoms is important to recognize the severity of dengue at an early stage because this can lead to proper case management, which saves lives.

We conclude that there is a direct link between knowledge about dengue preventive measures and container protection practice, whereas measures against adult mosquitoes are probably only used when people experience a mosquito nuisance problem. Closing the gap between knowledge and practice will remain an important challenge for dengue control, as well as defining dynamic targets for reduction of Ae. aegypti populations.

Received October 14, 2005. Accepted for publication November 29, 2005.

Acknowledgments: We thank the residents of Kon Tee and Na Bo Kham, Kamphaeng Phet, Thailand for participating in the KAP survey and allowing us to collect mosquitoes in their houses. The collaboration with the staff at the Public Health Offices of Kon Tee and Na Bo Kham and the local public health volunteers is greatly appreciated. We also thank the staff of the Kamphaeng Phet Entomology Laboratory of the Armed Forces Research Institute of Medical Science for their help in our studies. Jared Aldstadt, Arthur Getis, and Birgit van Benthem are acknowledged for their comments on an earlier version of the manuscript.

Financial support: This study was supported by grant AI-034533 from the National Institutes of Health.

^* Address correspondence to Constantianus J. M. Koenraadt, Department of Entomology, University of California, 1 Shields Avenue, Davis, CA 95616. E-mail: cjmkoenraadt{at}ucdavis.edu

Authors’ addresses: Constantianus J. M. Koenraadt and Thomas W. Scott, Department of Entomology, University of California, 1 Shields Avenue, Davis, CA 95616, Telephone: 530-754-4196, Fax: 530-752-1537, E-mails: cjmkoenraadt{at}ucdavis.edu and twscott{at}ucdavis.edu. Wieteke Tuiten, Ratana Sithiprasasna, Udom Kijchalao, and James W. Jones, Department of Entomology, U.S. Army Medical Component, Armed Forces Research Institute of Medical Sciences, 315/6 Rajvithi Road, Bangkok 10400, Thailand, Telephone: 66-2-644-4888, Fax: 66-2-354-7885, E-mails: ratanas{at}afrims.org, udomk{at}afrims.org, james.jones{at}afrims.org, and wtuiten{at}hotmail.com.

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