Rodent activity in municipal waste collection premises in Singapore: an analysis of risk factors using mixed-effects modelling.

Refuse storage and collection systems are potential sources of food and harbourage areas for rodents which transmit pathogens. We examined the factors associated with rodent activity in public housing municipal waste collection premises in a highly urbanized city-state. We analysed data from April 2019 to March 2020 in mixed-effects logistic regression models to examine the independent factors associated with rodent activity in central refuse chute rooms (CRCs), individual refuse chute (IRC) bin chambers and bin centres. We accounted for within-year patterns, repeated measures and nested effects. We observed a heterogeneous spatial distribution of rodent activity. Rodent droppings were strongly associated with rodent activity in CRCs (aOR: 6.20, 95% CI: 4.20-9.15), bin centres (aOR: 3.61, 95% CI: 1.70-7.64) and IRC bin chambers (aOR: 90.84, 95% CI: 70.13-117.67). Gnaw marks were positively associated with rodent activity in CRCs (aOR: 5.61, 95% CI: 3.55-8.97) and IRC bin chambers (aOR: 2.05, 95% CI: 1.43-2.95), as were rub marks in CRCs (aOR: 5.04, 95% CI: 3.44-7.37) and IRC bin chambers (aOR: 3.07, 95% CI: 1.74-5.42). Each burrow increased the odds of rodent sightings in bin centres (aOR: 1.03, 95% CI: 1.00-1.06). The odds of rodent sightings in an IRC bin chamber increased with every additional bin chute chamber within the same block (aOR: 1.04, 95% CI: 1.01-1.07). We identified several factors that well predicted rodent activity in waste collection premises. Municipal estate managers with limited resources can adopt a risk-based approach in tailoring the focus of their rodent control interventions.

Distribution and seasonal fluctuations of Ae. aegypti and Ae. albopictus larval and pupae in residential areas in an urban landscape.

Dengue, a vector-borne disease spread by Aedes mosquitoes, is a global threat. In the absence of an efficacious dengue vaccine, vector control is the key intervention tool in Singapore. A good understanding of vector habitats is essential to formulate operational strategies. We examined the distribution, long-term trend and seasonality of Aedes data collected during regulatory inspections in residences and public areas from 2008 to 2017. We also studied the seasonality of climate factors to understand their influence on the detection of Aedes-positive containers. The most frequently reported Aedes-positive containers were domestic containers, drains, discarded receptacles, ornamental containers, flower pot plates/trays, plants, gully traps, canvas/plastic sheet, bins, ground puddle, inspection chambers and roof tops/gutters. We found more Ae. aegypti and Ae. albopictus-positive containers per inspection in residences and public areas, respectively. The seasonality of Ae. aegypti-positive containers in residences and public areas coincided with that of mean temperature. However, the seasonality of Ae. albopictus-positive containers lagged by one month compared to that of mean temperature. Our study demonstrates the seasonal fluctuations of Aedes-positive containers in an urban environment. Understanding the distribution and seasonality of Aedes breeding helps to facilitate resource planning and community awareness to moderate dengue transmission.

The effectiveness of inspections on reported mosquito larval habitats in households: A case-control study.

BACKGROUND: Dengue is an arboviral disease that imposes substantial health and economic burdens across the globe. Vector control remains a key strategy in settings where Dengvaxia (a dengue vaccine) has not been licenced due to safety concerns and where mass immunization programmes are not cost-effective. Though inspections are used as part of arboviral disease control programmes, evidence of their impact on the entomological activity in households is sparse. METHODOLOGY/PRINCIPAL FINDINGS: We analysed nationally representative household inspection data collected from Singapore over a 3-year period, to determine the effect of inspections on reported mosquito larval habitats in households. A case was a household with a positive report of a mosquito larval habitat in its most recent inspection in 2017. A control was a household that was reported free of mosquito larvae in its most recent inspection in 2017. Using multivariable logistic regression, we analysed 3,205 cases and 557,044 controls. Households averaging three inspections per annum were associated with reduced odds of mosquito larval habitat reports [Adjusted Odds Ratio (AOR): 0.49, 95% Confidence Interval (95% CI): 0.38 to 0.63]. The effect of inspections declined with decreasing inspection frequencies but remained protective at lower levels. Longer intervals (30 to 36 months) between the most recent two successive inspections were associated with increased odds of mosquito larval habitat reports (AOR: 1.28, 95% CI: 1.06 to 1.56) compared to those carried out less than 6 months apart. Mosquito larval habitat reports exhibited a dependence on spatial and household-level characteristics such as the location of the community district, housing type and housing floor level. We observed a four-fold increase in the odds of mosquito larval habitat reports in households with an immediate previous report of larval activity compared to those that did not have one (AOR: 4.52, 95% CI: 3.67 to 5.56). CONCLUSIONS/SIGNIFICANCE: Our study confirms the protective effect of inspections on reported mosquito larval habitat reporting in households. Spatial, temporal and household-level characteristics should be accounted for in prioritizing vector control resources. Alternative strategies may help address recurrent entomological activity in households.