Dengue cases in Singapore fell to under 600 in September from 1,568 in May: NEA

Male Wolbachia-aedes aegypti mosquitos are released at a public housing estate test site in Singapore on 27 August 2020. (PHOTO: Reuters)
Male Wolbachia-aedes aegypti mosquitos are released at a public housing estate test site in Singapore on 27 August 2020. (PHOTO: Reuters)

SINGAPORE — The weekly number of reported dengue cases in Singapore fell from a high of 1,568 in May to under 600 in September, said the National Environment Agency (NEA) on Wednesday (28 September).

The number of dengue clusters also declined to 147 from a high of 422 in June while the total number of reported cases was 27,996 so far this year as of Wednesday.

About 11,300 mosquito breeding habitats were detected in the first half of this year, of which 63 per cent was detected in households, four per cent in construction sites, 25 per cent in public areas, and eight per cent in other premises types such as dormitories, factories, and schools.

NEA closed about 72 per cent of dengue clusters found between January and June.

These figures were released alongside NEA's Integrated Sustainability Report 2021/2022.

About 409,000 inspections were conducted by NEA islandwide in the first half of this year, including 2,800 inspections at construction sites. During the same period, NEA issued fines to 1,300 households for mosquito breeding, and 6,565 legal notices to homeowners and occupiers.

NEA also issued 70 stop work orders to construction sites and charged 28 contractors in court.

Singapore experienced early signs of a dengue outbreak in February, with weekly dengue cases rising to above 200. Some factors for the surge then include waning immunity, a high Aedes aegypti mosquito population, circulation of previously uncommon Dengue 3 virus serotype (DENV-3), as well as warm, rainy, and humid weather, said NEA.

Studies have also shown that Singapore population’s immunity towards dengue is low, said NEA. Nonetheless, the probability of getting a first infection each year is now lower at less than 1 per cent, compared with about 5 per cent in the 1970s and 10 per cent in the 1960s.

"Despite the unusual early rise in dengue cases this year, the collective efforts of stakeholders and the community have allowed us to manage the outbreak, without reaching the peak dengue case numbers seen in the huge 2020 outbreak," NEA added.

NEA, however, warned that weekly dengue cases remain high and persist beyond the traditional peak dengue season from June to October.

To complement existing dengue control efforts, NEA said it started the release of male Wolbachia-Aedes mosquitoes at eight additional field sites since July.

Since April, releases of these male mosquitoes at Tampines and Yishun have been expanded to cover the entire towns. High-risk areas in Choa Chu Kang and Bukit Batok also continued to see targeted releases of such mosquitoes.

"The results have been promising, with up to 98 per cent reduction in the Aedes aegypti mosquito population and up to 88 per cent reduction in dengue cases observed in Tampines and Yishun, after more than a year of releases," said NEA.

In 2021, Singapore recorded 96 local dengue cases per 100,000 population, according to NEA's annual report. In total, 5,258 cases were reported, almost seven times lower than the 35,266 cases reported in 2020.

Last year, NEA conducted 631,000 inspections for mosquito breeding, of which 6,300 were at construction sites.

A total of 11,000 enforcement actions were taken against premises owners and occupiers for mosquito breeding, including 690 enforcement actions, 43 stop work orders issued to construction sites, and charging of 64 contractors in court for repeat offences.

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