More than 4,000 people in Singapore have been infected with dengue fever this year - double the number of cases reported for the same period last year.
The surge in cases, ahead of the traditional peak dengue season between June and October, has been fuelled by several factors - the rise of a less common dengue virus serotype, as well as warmer temperatures and more rain which have caused the population of the Aedes aegypti mosquito to multiply.
"This unusually high number of cases outside the typical peak dengue period is a cause for concern for all of us. Entering the warmer months of the year, there could be more instances of transmission," said Environment and Water Resources Minister Masagos Zulkifli at the launch of the National Dengue Prevention Campaign in Ang Mo Kio yesterday.
The National Environment Agency's (NEA) annual campaign typically begins next month or in May, but starts earlier this year in view of the grimmer dengue outlook. The island has seen 300 to 400 new cases a week since the start of the year. There are now about 100 active dengue clusters islandwide, including 28 "red" clusters that have at least 10 cases. Parts of Jurong West and Ang Mo Kio Avenue 10 are in these high-risk areas.
Dengue fever is caused by four different virus serotypes, or strains. Outbreaks here tend to be caused by the DenV-1 serotype as well as DenV-2, the main dengue virus serotype here since 2016. But DenV-3 infections have been rising in the past four months. Last month, they made up 48 per cent of cases, almost double the 26 per cent for DenV-2 cases.
Mr Masagos said since Singapore has not had a dengue outbreak driven by DenV-3 in almost three decades, the population's immunity to this serotype is lower. It is "still too early" to tell if there has been a switch of predominant dengue virus type, and the NEA is monitoring the situation closely, he added.
"We have a less common dengue virus serotype emerging and lower immunity against it, and second, we have more Aedes mosquitoes carrying this virus. This has resulted in a higher number of dengue cases, which in turn increases the chances of dengue transmission. So that is the third reason for the surge in dengue cases we are seeing...
"If the three factors I mentioned persist, this number could rise beyond the historical weekly peak of 891 cases recorded in July 2014, during the peak season."
Dengue fever, which can cause a very high fever, severe headache and joint and muscle pain, claimed 20 lives last year.
Over the past three years, the detection rate of Aedes mosquito larval habitats in homes has also gone up by 90 per cent - which Mr Masagos attributed to "better surveillance and analytics capabilities".
The NEA has been taking steps to fight dengue, he said.
From January to last month, it conducted 161,000 inspections in public areas and housing estates and found about 3,200 mosquito-breeding habitats, most of which were in people's homes. At the start of the year, the NEA also laid 14,000 Gravitraps in newly completed Housing Board blocks and landed housing estates. More than 64,000 of these devices islandwide trap female Aedes adult mosquitoes that are looking for places to lay their eggs, and also stop young mosquitoes in these traps from emerging.
Everyone must continue to do their part to keep the community safe, Mr Masagos said. He added that the SG Clean campaign launched last month "addresses the immediate risks from Covid-19, (but) also sets out to improve public hygiene and cleanliness for the long term".
IT technician Viknesh Jayasekaran, 34, who lives near a high-risk dengue cluster in Ang Mo Kio, takes the usual precautions - leaving pails upturned and emptying water from plates below plant pots as Aedes mosquitoes can breed in bodies of stagnant water as small as a 20-cent coin.