Knowledge and practice of household mosquito breeding control measures between a dengue hotspot and non-hotspot in Singapore.

INTRODUCTION: The aim of this study was to compare the knowledge and practices of household mosquito-breeding control measures between a dengue hotspot (HS) and a non-hotspot (NHS). MATERIALS AND METHODS: Eight hundred households were randomly sampled from HS and NHS areas, and an National Environment Agency (NEA) questionnaire was administered to heads of the households. Interviewers were blinded to the dengue status of households. We included subjects aged above 16 years, who were communicative and currently living in the household. Chi-square test was used to compare proportions and multiple logistic regression was used to adjust for socio-demographic differences between both areas. RESULTS: The overall response rate was 59.0% (n = 472). There were significant differences in gender, educational level, employment status and housing type between HS and NHS (all P <0.05). NHS residents were less knowledgeable in 6 out of 8 NEA-recommended anti-mosquito breeding actions: changing water in vase/bowls [AOR (adjusted OR), 0.20; CI, 0.08-0.47; P <0.01], adding sand granular insecticide to water [AOR, 0.49; CI, 0.31-0.71; P <0.01], turning over pails when not in use [AOR, 0.39; CI, 0.17-0.89; P = 0.02], removing flower pot/plates [AOR, 0.35; CI, 0.18-0.67; P <0.01], removing water in flower pot/plates [AOR, 0.36; CI, 0.17-0.75; P <0.01] and putting insecticide in roof gutters [AOR 0.36; CI, 0.13-0.98; P = 0.04]. Hotspot residents reported better practice of only 2 out of 8 NEA-recommended mosquito-breeding control measures: changing water in vases or bowls on alternate days [AOR, 2.74; CI, 1.51-4.96; P <0.01] and removing water from flower pot plates on alternate days [AOR, 1.95; CI, 1.01-3.77; P = 0.05]. CONCLUSION: More HS residents were knowledgeable and reported practicing mosquito-breeding control measures compared to NHS residents. However, a knowledge-practice gap still existed.

Climate variability and increase in intensity and magnitude of dengue incidence in Singapore.

INTRODUCTION: Dengue is currently a major public health burden in Asia Pacific Region. This study aims to establish an association between dengue incidence, mean temperature and precipitation, and further discuss how weather predictors influence the increase in intensity and magnitude of dengue in Singapore during the period 2000-2007. MATERIALS AND METHODS: Weekly dengue incidence data, daily mean temperature and precipitation and the midyear population data in Singapore during 2000-2007 were retrieved and analysed. We employed a time series Poisson regression model including time factors such as time trends, lagged terms of weather predictors, considered autocorrelation, and accounted for changes in population size by offsetting. RESULTS: The weekly mean temperature and cumulative precipitation were statistically significant related to the increases of dengue incidence in Singapore. Our findings showed that dengue incidence increased linearly at time lag of 5-16 and 5-20 weeks succeeding elevated temperature and precipitation, respectively. However, negative association occurred at lag week 17-20 with low weekly mean temperature as well as lag week 1-4 and 17-20 with low cumulative precipitation. DISCUSSION: As Singapore experienced higher weekly mean temperature and cumulative precipitation in the years 2004-2007, our results signified hazardous impacts of climate factors on the increase in intensity and magnitude of dengue cases. The ongoing global climate change might potentially increase the burden of dengue fever infection in near future.

Dengue virus infection rate in field populations of female Aedes aegypti and Aedes albopictus in Singapore.

We developed a single-step reverse transcription-polymerase chain reaction (RT-PCR) followed by a semi-nested PCR using an upstream consensus primer and four type-specific primers within the non-structural protein gene (NS3) of dengue viruses to type dengue viruses in field populations of female Aedes mosquitoes. This yielded diagnostic fragments of 169, 362, 265 and 426 base pairs for dengue virus types 1, 2, 3 and 4, respectively. From 1997 to 2000, 54 (6.9%) of 781 Aedes aegypti and 67 (2.9%) of 2256 Aedes albopictus screened were positive for dengue viruses, with a declining trend. The most common dengue virus type detected in the Aedes mosquitoes was dengue-1. Details on the change of one serotype to another in the mosquito population over three consecutive years are discussed.