Falling immunity and better detection behind rise in dengue cases: Expert

NEA inspection officer Sindhusha Selvakumar checking areas that could be mosquito breeding spots in May. PHOTO: ST FILE

SINGAPORE - The spike in dengue cases this year can be attributed to lower immunity in the population from historical falls in infections and better detection of cases, said a public health expert.

Better diagnostics have led to more infections being diagnosed, Associate Professor Alex Cook from the National University of Singapore's Saw Swee Hock School of Public Health told The Straits Times.

More than 19,000 cases of dengue have been reported so far in 2022, based on figures from the National Environment Agency (NEA) - nearly a fourfold increase from the 5,258 cases reported last year.

Prof Cook said the soaring rate of dengue cases this year is mainly due to conducive weather conditions for mosquito breeding and the circulation of DenV-3 virus, to which the population has lower immunity.

The dengue tally to date is also more than half of the 35,315 cases reported in 2020 - the worst dengue outbreak in Singapore's history, claiming 28 lives.

There have been four deaths so far in 2022, said Senior Parliamentary Secretary for Sustainability and the Environment Baey Yam Keng earlier this month.

There are 343 dengue clusters still active, with 119 of these having 10 or more cases and designated as high risk. The largest, at the Toh Tuck estate along Upper Bukit Timah Road, has recorded 529 cases.

At construction sites, 73 stop-work orders have been issued this year. Five are still active as of last Friday.

The NEA has carried out around 389,000 inspections in the first half of this year, uncovering 10,800 mosquito breeding habitats. It noted that at least half of these breeding sites are found in homes.

On their part, home owners can opt for devices like In2Care's mosquito traps, which utilise a fungal-based larvicide that kills mosquito larvae before they reach the pupal stage. The larvicide is also spread to other breeding sites via female mosquitoes.

The product is not yet licensed for consumer use as the trap needs to be professionally maintained to ensure its efficacy, but Singaporeans who wish to deploy it in their homes can do so through pest control companies such as Rentokil, PestBusters or Anticimex.

Prof Cook said Singaporeans could take precautions such as wearing long sleeves or applying mosquito repellent. Spraying store-bought insecticide indoors is another option, he added.

"There are places the mosquito likes to rest so spraying there can help reduce the density. Finally, you might consider installing anti-mosquito screens on windows like they do in Japan," Prof Cook said.

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