SINGAPORE — The number of dengue cases this year is expected to exceed the caseload reported last year, even surpassing the peak of 22,170 cases that was reported in 2013, the National Environment Agency (NEA) said.

In a statement on Wednesday (June 3), the agency also said that there were 9,261 dengue cases reported as of June 2 this year, the highest for the same period of the year since 2013, which saw the largest outbreak year in Singapore’s recent history.

NEA also observed a five-fold increase in the incidence of Aedes mosquito larvae detected in homes and common corridors in residential areas during the two-month circuit breaker period in April and May compared with the two months before that.

The circuit breaker, which ended on Monday, was the Singapore Government’s term for stay-home curbs, to restrict social interaction and non-essential business activities. People had to work from home where possible and office buildings were largely closed.

NEA said that the weekly number of reported dengue cases this year has climbed steadily from 300 to 400 cases in the first four months of the year to 735 cases last week.

It highlighted that Singapore has not seen such a high weekly figure since the peak years in 2013 and 2014.

“The number of dengue cases this year is expected to exceed the 15,998 cases reported in 2019, and may even surpass the 22,170 cases reported in 2013,” it said, adding that the Ministry of Health (MOH) had been notified of 12 dengue deaths this year alone.

The victims were aged between 56 and 80, and of the 12 who died, 10 had worked or resided in dengue cluster areas, NEA said.

WHY THE JUMP IN CASES

NEA said that a “confluence of factors” had contributed to the recent spike: A less common dengue strain had surfaced and increased, warmer weather that ties in with the traditional dengue peak period, as well as a spike in cases that coincided with the circuit breaker period.

The agency’s Gravitrap surveillance system has also revealed more areas with high Aedes aegypti mosquito populations.

1. Increase in a less common dengue strain

NEA said that there had been an increase in the less common dengue virus serotype 3 (DENV-3) since the start of the year.

This strain was last dominant in Singapore about three decades ago, which means that there is low immunity among the human population and a rapid disease transmission.

“This likely explains the unusually high number of weekly cases — hovering between 300 and 400 — since the start of the year.”

2. Traditional dengue peak period

Singapore is entering the traditional dengue peak season, with the warmer weather facilitating faster growth of the Aedes mosquito and dengue virus, increasing the chances of disease spread.  

3. Cases coincided with circuit breaker period

The dengue spike occurred over a short four-week period since early May.

The Aedes mosquito dwells mainly in indoor spaces and primarily bites during the day.

“With a shift in human concentration from offices to homes, more people staying at home during the day also means more blood meals for the female mosquitoes, especially in residential areas where the mosquito population is also high,” NEA said, adding that together with the availability of breeding habitats for larvae, this produced even more mosquitoes.

WHAT HAS BEEN DONE FOR PREVENTION

NEA said that it had taken a “multi-pronged approach to dengue control”, comprising vector control measures, engagement with stakeholders, as well as community mobilisation and public communications.

In anticipation of the surge in cases this year, it has also:

• Rolled out the Gravitrap surveillance system to housing estates with landed property

• Brought forward the National Dengue Prevention Campaign launch to March

• Ramped up dengue prevention outreach via digital and mobile platforms

• Put up more dengue alert banners at cluster areas

• Worked with MOH, polyclinics and general practitioners to provide more than 300,000 bottles of mosquito repellent for distribution to patients suspected to have dengue

WHAT IS URGENTLY NEEDED

NEA said that it urgently seeks the community’s support to ensure that their homes and gardens in their compounds are free of possible breeding grounds for mosquitoes and they should use aerosol insecticide spray and mosquito repellent to protect themselves and their families.

From January to May, NEA had conducted about 341,000 checks for mosquito breeding islandwide and uncovered about 7,800 such habitats.

Homeowners and occupants are strongly urged to do their part as well, NEA said, by paying close attention to any mosquito breeding spots or adult mosquitoes present in their homes, and taking the necessary steps to prevent or remove them.

It added that all residents living in dengue cluster areas are strongly encouraged to cooperate with NEA officers, and facilitate their checks and indoor misting in their homes.

“Allowing NEA to access all homes in dengue cluster areas as quickly as possible helps keep your family members, neighbours and the community safe from being infected with the dengue virus,” it said.

To help residents do their part to remind family members and neighbours to regularly inspect their own homes, NEA has developed a “Check and Protect checklist” highlighting the common mosquito breeding spots. The checklist will be distributed via grassroots and partners’ networks and is also available online for download. 

Mr Chew Ming Fai, director-general of NEA’s environmental public health division, said that even as Singapore continues to manage the Covid-19 crisis, “we need to be mindful that dengue is another serious public health threat that the country faces”.

“Lack of care or diligence in maintaining one’s premises or home could easily lead to mosquito breeding, putting the whole community at risk. Weekly dengue case numbers are likely to continue to rise, and more dengue clusters will form in the coming weeks to months,” he said.

TWO-FOLD INCREASE AT CONSTRUCTION SITES

Preventive surveillance has also been stepped up at construction sites, given their closure during the circuit breaker period.

NEA said that it has prioritised inspections at higher-risk construction sites such as those within dengue clusters and residential areas, as well as sites with past records of having been found breeding mosquitoes.

Since early April, 82 per cent of these sites have been inspected and it has observed a two-fold increase in the incidence of Aedes mosquito larvae detected at construction sites during the circuit breaker period.

From January to May this year, 52 summonses and two stop-work orders were issued to construction sites, and two contractors will be charged for repeat offences.

Mr Chew said: “NEA will continue with our inspection and enforcement efforts, and we will not hesitate to take action against anyone found to have created conditions favourable for the propagation or harbouring of vectors. All of us must do our part in our collective fight against dengue.”