Demographic, economic and behavioural factors are central features underpinning the successful management and biological control of dengue. This study aimed to examine these factors and their association with the seroprevalence of this disease. We conducted a cross-sectional telephone survey of households in a 3 km radius of the schools where we had conducted serological tests on the student population in a previous study. Households were surveyed about their socio-demographics, knowledge, practices, and Health Belief Model (HBM) constructs. The results were then associated with the prevalence rate of dengue in the community, as marked by IgG seropositivity of the students who attended school there. A total of 1,400 complete responses were obtained. The community' s IgG seropositivity was significantly positively associated with high household monthly income, high-rise residential building type, high surrounding vegetation density, rural locality, high perceived severity and susceptibility, perceived barriers to prevention, knowing that a neighbour has dengue, frequent fogging and a higher level of knowledge about dengue. In the multivariate analyses, three major correlates of the presence of IgG seropositivity in the community: (1) high-rise residential apartment house type or condominium buildings; (2) the main construct of the HBM, perceived severity and susceptibility; and (3) the additional constructs of the HBM, lack of preventive measures from the community level and having a neighbour with dengue as a cue to action. Weak correlations were found between self-practices to prevent dengue and the level of dengue seropositivity in the community, and between HBM constructs and knowledge (r = 0. 09). The residential environment factor and the constructs of the HBM are useful and important elements in developing interventions to prevent and control dengue. The study also sheds light on the importance of the need for approaches that ensure the translation of knowledge into practice.
The incidence of dengue has grown dramatically in recent decades [1]. Over 2. 5 billion people, 40% of the world' s population, are at risk from dengue, and each year an estimated 50–100 million dengue infections are reported worldwide [1]. The disease is currently endemic in more than 125 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific [1]. Since the first reported case of dengue fever in Malaysia in 1902, dengue has remained a serious public health problem in this country. Malaysia has experienced several major outbreaks, which were reported in 1974,1978,1982 and 1990 [2]. Likewise in Malaysia, the incidence of dengue fever and its more severe forms have increased dramatically in recent decades. The incidence rate of dengue shows an increasing trend from 44. 3 cases/100,000 population in 1999 to 181 cases/100,000 population in 2007 [3]. High dengue IgG seropositivity (>91%) was found in a sample of Malaysian adults aged 35 to 74 years old in a recent study [4]. Serological tests conducted in Lundu District in Sarawak, Malaysia, found that in >23% of 215 samples, individuals had a history of dengue [5]. In another study, a nationwide sample of 1,410 children aged 7 to 18 years was surveyed and 11. 0% were found to be positive for dengue IgG (Tiong et al. , unpublished data). Among the most frequently applied methods of controlling or preventing dengue is the control of dengue virus transmission through mosquito reduction activities. Human behaviour is an important contributor to creating breeding grounds for mosquitoes and sustaining mosquito populations [6]. It has long been recognized that socio-demographic characteristics, beliefs and practices about dengue have an impact on dengue prevention and control. The basic concepts of the Health Belief Model (HBM) feature individual consideration of the likelihood (susceptibility) and seriousness (severity) of illness and the capacity of the individual to adopt the desired behaviour to prevent it [7]. Since its original conception, two additional concepts have been added to the HBM: self-efficacy, or one' s confidence in the ability to successfully perform an action; and cues to action, external events that prompt readiness to make a health change [8]. A handful of studies have specifically applied the HBM in attempts to understand perceptions of risk and sustained dengue prevention [9]–[11]. In the context of health communication strategies for dengue prevention and control, the HBM provides a framework for understanding how to effectively structure messages and influence behavioural change [12]. Previous studies have primarily focused on investigating the constructs of the HBM in conceptualizing health beliefs and knowledge about the threat of dengue, the barriers to engaging in the desired preventive behaviour, and the subsequent development of self-efficacy to initiate the desired behaviours. This study differs from previous field investigations in that it focuses on investigating the HBM constructs and their association with the seroprevalence of dengue virus-specific IgG in the community. To the best of our knowledge, such a study has never been conducted elsewhere.
The seroprevalence data were obtained from our previous study (Tiong et al. , unpublished data). Between 2008 and 2009, anonymized serum samples of school children, aged 7 to 18, from 26 schools throughout Malaysia were examined for dengue virus-specific IgG. Dengue IgG capture ELISA (Standard Diagnostics, Korea, Cat. no. 11EK10) was used to test for the presence of anti-dengue-specific IgG antibodies. Of the 1,411 samples from 26 schools, 156 (11%) were positive for dengue-specific IgG antibodies. The prevalence of seropositivity for dengue-specific IgG in the student population, calculated for each school, ranged from 0% to 25±1%. The percentage of seropositivity for dengue-specific IgG in the surrounding community (within 3 km) was assumed to be the same as that of the student population in the nearby school. Households within a 3 km radius of a school were therefore assigned a corresponding percentage of seropositivity for dengue-specific IgG. In the current study, the level of IgG seropositivity in the study participants was categorized as being ‘absent’ or ‘present’. Further, a K-means cluster analysis procedure was also used to identify groups by the percentage of positive IgG results in the study participants. The households in a 3 km radius of the schools were surveyed about their knowledge and health belief constructs, the results of which were associated with the absence or presence of seropositivity and with the seropositivity groups identified in cluster analysis. The seroprevalence of dengue amongst the students was used as a surrogate for the prevalence of dengue in the community, as students were not likely to have extensively travelled outside their respective communities. The community around the school was chosen because Malaysian schools usually admit only those students living within a 10 km radius of the respective school. Because of the unmanageably large number of households within a 10 km radius of the schools, this study surveyed only those households within a 3 km radius. The study samples for the present study were households within a 3 km radius of the schools. Residential communities within a 3 km radius of the schools were first identified. Subsequently, we performed a cross-sectional study by contacting all households in the identified residential community with a registered landline telephone (which served as the study sample of the population). To be eligible for a telephone interview, participants had to be Malaysian, aged between 18 and 60 years old, and resident in the contacted household. Only one person per household was surveyed. If more than one eligible person was found in a household, one person was selected randomly by using a random number table. Interviews were conducted between 5. 30 p. m. and 10. 00 p. m. on weekdays in order to avoid over-representation of unemployed participants, and from 10. 00 a. m. to 7. 00 p. m. on weekends or on public holidays. Interviewers made three attempts to call unanswered telephones on different days before regarding them as non-responses. After the survey questions were constructed, a panel of experts, consisting of four members, was assembled to investigate the content validity of the survey. Two parameters were measured in the content validation study: (1) the necessity of each survey item, and (2) the clarity of each survey statement. The panel was asked to comment independently on the necessity and clarity of the items in order to calculate the content validity ratio (CVR) and the content validity index (CVI), respectively. The necessity of the items was assessed by using a three-point rating scale: (1) essential; (2) useful, but not essential; and (3) not necessary. The clarity of the items was also assessed by using a 3-point rating scale: (1) clear, (2) item needs revision, and (3) not clear. Following the experts' assessments, a CVR for the total scale was computed. The CVR in this study for the total scale was 0. 61, indicating a satisfactory result. For the necessity parameter, all CVRs were 1. 0, thus leading to a CVI of 1. 0. The overall CVI for the clarity of survey statements was 0. 87. A satisfactory level of agreement was found (CVI>0. 80) among panellists, suggesting that the scale had good content validity [13]. Several questions were rephrased, as suggested by the panellists, to improve clarity. The modified questionnaire was executed in the form of a preliminary study, which included a random sample of 50 people to investigate the possible problems of the questionnaire and its reliability. The questionnaire inquired about socio-demographic characteristics, house and surrounding environment, beliefs regarding dengue fever, self-reported preventive practices against dengue fever and knowledge of dengue fever. Belief questions were based on the HBM constructs [7]: Self-reported practices for the prevention and control of dengue fever, namely (1) prevention of mosquito breeding and (2) prevention of mosquito bites, were assessed by using 6-item and 7-item questions, respectively. The options for practices (not at all, rarely, sometimes, often, and not applicable) were assigned penalty points of 4,3, 2,1 and 0, respectively. The possible scores ranged from 0 to 36 for mosquito breeding preventive practices, and 0 to 28 for mosquito bite preventive practices. A higher number of penalty points indicates fewer preventive practices. As the dengue prevention scales were newly developed, an initial pilot test was performed to ensure test-retest reliability, the result of which was found to be acceptable (correlation coefficient >0. 70). Cronbach' s alpha measurements were also performed. Cronbach' s alpha coefficients for prevention of mosquito breeding and mosquito bites were 0. 791 and 0. 898, respectively, demonstrating good internal consistency. The scale for the measurement of knowledge of dengue fever consisted of 43 items. For each statement, the respondents could choose between three response categories: yes, no and don' t know. For the analyses, the responses were scored as 1 for a correct response and 0 for an incorrect response or a ‘don' t know’ response. Possible scores ranged from 0 to 43. The higher scores indicate greater knowledge about dengue fever. Cronbach' s alpha was 0. 916, showing high internal consistency. The study was approved by the Medical Ethics Committee of the University of Malaya Medical Centre, Kuala Lumpur, Malaysia (MEC Ref No. 896. 15). Due care was taken to ensure that all those who agreed to participate in the study did so voluntarily. Respondents were assured that their responses would remain confidential and anonymous, and that they were free to withdraw from the interview at any time. As written informed consent is not practical in a telephone survey, verbal informed consent was obtained from the respondents before the beginning of an interview. The verbal consent procedure was approved by the Medical Ethics Committee. The 26 schools throughout Malaysia were sampled randomly from six zones (North, East, West, Centre and South of Peninsular Malaysia, as well as Sabah in East Malaysia). Therefore, conventional statistical analyses with underlying distributional assumptions were inappropriate for variance estimation and statistical testing because of the multistage probability sampling design. Sampling weights were incorporated into the analyses to produce representative estimates. Each observation corresponding to the IgG of the respective school was proportionally weighted according to the overall school samples in the respective zone before analysis to account for the complex sampling design. The dependent variable (percentage of positive IgG) corresponding to each respondent was compared with the independent variable (socio-demographic characteristics, HBM constructs, dengue prevention practices and knowledge) by using t-test analysis, analysis of variance or chi-square analysis to see how the variables were associated independently of level of seroprevalence. In multivariate analysis, multiple linear regression standard errors are computed by using a sandwich estimator. A generalized linear model was used in which the outcome was the presence of a level of dengue seroprevalence vs. its absence. The covariance matrix was estimated by using the robust estimator method. This sandwich standard error estimator assumes independence of the clusters. Correlations of individual level data were conducted with Spearman' s rank correlation coefficient to examine the association between self-reported practices to prevent mosquito breeding and mosquito bites and (1) HBM constructs and (2) knowledge score. Effect sizes of 0. 20 or lower were considered to demonstrate ‘small’ relationships, while those ranging from 0. 30 to 0. 50 were considered to demonstrate ‘medium’ relationships and those of 0. 80 or greater ‘large’ relationships [14]. All statistical analyses were performed with SPSS 16. 0 (SPSS Inc. , Chicago, IL). In all analyses, a P-value of less than 0. 05 was considered statistically significant.
There were no significant differences in the percentage of positive IgG results in the community by ethnicity, gender, educational level or household size (Table 1). Dengue-specific IgG was present in 83. 0% of the group earning a household income of more than MYR4000 monthly (USD1313) and in 70. 4% of the group earning a household income of less than MYR2000 monthly (USD657; P<0. 001). A significantly higher proportion of respondents from the community presenting dengue IgG seropositivity were found to be residing in high-rise residential apartment or condominium buildings than in single (67. 9%) or terraced (61. 1%) houses. There were no clear ascending or descending trends between the proportion of respondents with dengue IgG present and the surrounding vegetation density levels reported, but participants reporting no vegetation in the surrounding environment were found to have the highest proportion of dengue IgG present (82. 1%) compared with those reporting a high vegetation density in the surrounding environment (77. 1%). The proportion of respondents with dengue IgG present was significantly higher among those from high-rise apartment or condominium buildings who reported moderate surrounding vegetation density (66. 0%) than it was for those who reported no vegetation density (15. 0%). The proportion of respondents with dengue IgG present was also significantly higher in rural than in urban areas (76. 5% versus 55. 4%). A higher proportion of rural respondents (44. 7%) reported a high level of vegetation density in their surrounding environment than did their urban counterparts (15. 8%). The mean (SD) rating of perceived severity of dengue fever on a scale from 1 to 10 was 7. 45 (SD = 2. 90) for respondents from communities where positive dengue IgG results were present and 6. 88 (3. 58) for respondents from communities where positive dengue IgG results were absent. Among respondents from communities where dengue IgG was present, the majority (81. 7%) rated the severity of dengue fever as 7 and 8. The mean (and SD) rating of the perceived susceptibility score was 5. 40 (SD = 2. 32) for respondents from communities where dengue IgG was present and 5. 18 (SD = 2. 52) for respondents from communities where dengue IgG was absent. The mean (SD) rating for the perceived barriers to sustain dengue prevention was also higher for respondents from communities where dengue IgG was present (4. 48, SD = 2. 39) than for respondents from communities where positive dengue IgG was absent (3. 79, SD = 2. 70). A higher proportion of respondents from communities where positive dengue IgG results were present reported that they either strongly agreed or agreed (78. 3%) that they lacked efficacy in taking preventive measures, as compared with respondents from communities where positive dengue IgG results were absent (21. 7%). Mosquito problems in the neighbourhood were reported as severe by 84. 9% respondents from communities where dengue IgG was present compared with only 15. 1% among respondents from communities where dengue IgG was absent. A higher proportion of respondents from communities where dengue IgG seropositivity was present (79. 4%) reported that they were aware that dengue was in their community, as compared with respondents from communities where dengue IgG was absent (20. 6%). Respondents from communities where dengue IgG was present reported a higher frequency of mosquito fogging in their community than did those from communities where dengue IgG was absent. A higher proportion of respondents from communities where positive dengue IgG results were present reported that they either strongly agreed or agreed (75. 6%) that there was a lack of preventive measures at the community level, as compared with respondents from communities where positive IgG results were absent (24. 4%). Similarly, a higher proportion of respondents from communities where IgG was present reported that they either strongly agreed or agreed (74. 1%) that there was a lack of preventive measures from the authorities, as compared with respondents from communities where IgG was absent (25. 9%). Thirty-seven per cent of respondents (350 of 944) did not periodically examine mosquito breeding places in their surroundings, 20% (167 of 849) did not cover their water storage containers, and 9% (86 out of 959) did not periodically change water stored at home. The total responses do not add up to 1,400 because some respondents did not practise storing water at home. A higher proportion of urban respondents (53. 9%) did not practise storing water compared with their rural counterparts (34. 4%). The mean (SD) penalty points for self-reported practices to prevent mosquito breeding was slightly higher among respondents from communities where positive dengue IgG results were present (13. 8, SD = 6. 7) than among respondents from communities where positive IgG results were absent (13. 2, SD = 5. 9). Using cluster analysis, we identified three distinct percentages of positive IgG seropositivity clusters. Table 2 shows the characteristic differences of respondents in three subgroups by percentage level of IgG (%) identified by cluster analysis. Cluster I, consisting of nine schools, has the lowest mean percentage of IgG (2. 37, SD±2. 39), whereas cluster III (total of six schools) has the highest mean percentage of IgG (25. 2, SD±3. 02). Cluster III had a higher proportion of high-rise house types (15. 6%) and village houses (61. 7%). Across clusters (Cluster I to Cluster III), an increasing proportion of respondents reported “a lot” of vegetation density. Likewise, an increasing proportion of respondents across clusters agreed that there was a lack of preventive measures at the community level and a lack of self-practice to prevent mosquito bites, as well as fogging. In contrast, we found a decreasing proportion of respondents with a high knowledge score from Cluster I to Cluster III. The Spearman correlation between scores for self-prevention practices and the constructs of the HBM, and between scores for self-preservation practices and knowledge scores, are shown in Table 3. The effect size, Spearman' s rho, indicates that the correlations between self-prevention practices (both prevention against mosquito breeding and against mosquito bites) and the constructs of the HBM can be considered a small effect, according to Cohen' s criteria on effect size. Significant small effect sizes were also found in the correlations between knowledge scores and preventive practices. Findings from multivariate logistic regression analysis (Table 1) indicate that the income group of MYR2001–4000 monthly (USD757-1313) was less likely than the income group above MYR4000 monthly (odds ratio [OR] = 0. 34,95% CI, 0. 22–0. 86, P<0. 01) to be seropositive for dengue IgG. Likewise, the income group below MYR2000 monthly was also less likely than the group above MYR4000 monthly (USD1313) to be seropositive for dengue IgG (OR = 0. 49,95% CI, 0. 34–0. 99, P<0. 05). Compared with those who reported a high level of vegetation density, those who reported moderate vegetation density (OR = 0. 62,95% CI, 0. 40–0. 98, P<0. 05) had a lower likelihood of being seropositive for dengue IgG. Those living in an urban area (OR = 0. 40,95% CI, 0. 30–0. 74, P<0. 001) had a lower likelihood of being seropositive for dengue IgG compared with those living in the reference rural area. The results of multivariate logistic regression analysis also indicated that the two main constructs of the HBM (perceived severity and susceptibility) were significant correlates of seropositivity for dengue IgG. Those with a lower perceived severity (level of severity 7–8) had a higher likelihood (OR = 1. 84,95% CI, 1. 25–2. 87, P<0. 001) of being seropositive for dengue IgG compared with those with a reference level of severity of 9–10. Likewise, those with a lower perceived susceptibility (level 3–4) had a higher likelihood (OR = 4. 50,95% CI, 1. 95–10. 99, P<0. 01) of being seropositive for dengue IgG compared with those with a reference level of 9–10. Having perceived barriers to sustain prevention (on a scale of 1–10) was not found to be significantly associated with being seropositive for dengue IgG in the logistic regression model. Respondents who rated the mosquito problem as' moderate' had a lower likelihood of being dengue seropositive (OR = 0. 45,95% CI, 0. 20–0. 97, P<0. 05) than did those who rated it as' severe' . Respondents who knew dengue was in their community had an increased likelihood of being dengue seropositive (OR = 1. 45,95% CI, 1. 28–2. 53, P<0. 01). There was a significant relationship between the gradual increase in the likelihood of being seropositive for dengue IgG and the frequency of fogging. Self-reported practices to prevent mosquito breeding was not a significant correlate of being seropositive for dengue IgG; however, having lower mean penalty points in the prevention of mosquito bites was associated with a lower likelihood of being seropositive for dengue IgG (OR = 0. 54,95% CI, 0. 49–0. 98, P<0. 001). Lack of preventive measures from authorities was not a significant correlate of being seropositive for dengue IgG; however, lack of preventive measures at the community level was significantly associated with IgG seropositivity (OR = 3. 1 95% CI, 1. 58–3. 85, P<0. 001). A low mean knowledge score (0–14) was associated with a lower likelihood of seropositivity for dengue IgG (OR = 0. 30,95% CI, 0. 25–0. 65, P<0. 001).
Our multivariate analyses revealed three major correlates of IgG seropositivity that should be the prime focus in dengue prevention and control: (1) high-rise residential apartment or condominium building house type; (2) the main construct of the HBM, perceived severity and susceptibility; and (3) the additional constructs of the HBM, lack of preventive measures at the community level and knowing a neighbour has dengue as a cue to action. These findings also suggest that constructs of the HBM can be integrated as ways of motivating the adoption of preventive practices against dengue, and they may work best by complementing other advocacy and mobilization approaches. Another significant outcome of this study is that it sheds light on the importance of the need for approaches that ensure the translation of knowledge into practice. Most important, the findings have profound implications for future studies that should seek more accurate and confirmatory evidence by investigating the socio-demographic and HBM constructs and their association with individual levels of IgG seropositivity.
Demographic, economic and behavioural factors are important to successful control of dengue. This study aimed to examine these factors and their association with the prevalence rate of dengue in a community marked by IgG seropositivity of students attending schools there, as assessed in our previous study. Telephone interviewing was used to try to reach the households in a 3 km radius of the schools where serological tests were conducted. Results showed three major correlates of the presence of IgG seropositivity in the community: (1) high-rise residential apartment house type or condominium buildings; (2) the main construct of the HBM, perceived severity and susceptibility; and (3) the additional constructs of the HBM, lack of preventive measures at the community level and having a neighbour with dengue as a cue to action. The residential environment factor and the constructs of the HBM are useful and important elements in developing interventions to prevent and control dengue.
biology and life sciences
behavior
psychology
social sciences
Community Knowledge, Health Beliefs, Practices and Experiences Related to Dengue Fever and Its Association with IgG Seropositivity