Risk of surge in dengue cases as previously dominant virus strain rapidly spreading: NEA

SINGAPORE - There is a risk of a surge in dengue cases in the coming months, as mosquitoes have been rapidly spreading a previously dominant virus strain, DenV-1.

The National Environment Agency (NEA) has seen an increase in DenV-1 cases over the past two months, replacing the DenV-3 serotype which drove Singapore's dengue outbreak in 2022 and mainly contributed to cases in the first half of 2023.

In July, the proportion of DenV-1 cases was about 55 per cent, more than thrice the amount of DenV-3 cases, which stood at 17 per cent, said the NEA on Wednesday (Sept 6).

"The rise in proportion of a previously less prevalent dengue virus serotype is of concern, as this has historically been associated with a surge in dengue cases months later," NEA said.

As at Sept 5, more than 6,200 dengue cases have been reported in 2023. In 2022, a total of 32,325 dengue cases were reported, the second highest number of cases in a year. The record high was 35,315 cases in 2020.

Before the DenV-3 serotype became prevalent from late 2021, the dominant strains in the past were DenV-1 and DenV-2. There are a total of four distinct dengue virus variations, or serotypes, which means a person can be infected with dengue up to four times. Repeated infections in a person increase the risk of severe dengue fever.

DenV-3 was a less common strain that many residents were vulnerable to, due to lack of exposure and immunity.

There are currently 48 active dengue clusters, 13 of which are large clusters with 10 or more cases. The clusters at Science Park Drive (29 cases) and Lentor Loop (24 cases) have a fast rate of dengue transmission, noted NEA.

The largest cluster at Lorong 1 and Lorong 2 Toa Payoh, with 319 cases to date, are among some clusters with persistent transmission.

NEA said: "There is a risk of a surge in dengue cases as Denv-1 gains dominance against a backdrop of high weekly dengue cases, several large and persistent dengue clusters, and high Aedes mosquito populations in many places."

Apart from removing stagnant water, the agency urged households and offices, especially those within existing clusters, to take measures to prevent infection. These include applying insect repellent regularly, wearing long-sleeve tops and long pants, and spraying insecticide in dark corners of the house.

NEA also urged people diagnosed with or suspected to be infected with dengue to take those measures to prevent spreading the virus to mosquitoes and others in their neighbourhoods.

In dengue clusters, about 68 per cent of Aedes mosquito breeding sites detected were in homes, with 29 per cent at public areas, and the rest at construction sites and other areas.

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This article was first published in The Straits Times. Permission required for reproduction.