The danger from dengue is far from over even as the number of cases in Singapore has fallen, the National Environment Agency (NEA) warned yesterday.
There were 156 cases last week, compared with 236 infections a week in mid-December.
But the population of the Aedes aegypti mosquito, the vector that spreads dengue, increased by 8 per cent last month.
On top of that, DenV-3 and DenV-4 – two dengue serotypes that are less commonly seen here – have increased and now account for more than half the infections.
There are four dengue serotypes. People who have been infected are protected against only that type, and not the other three, which means they remain susceptible.
Over the three decades prior to last year, all dengue outbreaks here were caused by either DenV-1 or, since 2016, by DenV-2. As neither DenV-3 nor DenV-4 has infected large numbers of people in the past, the vast majority of the population would be susceptible.
The rise of DenV-3 last year likely contributed to the largest dengue outbreak Singapore has ever seen, with a total of 35,315 people infected and at least 29 people dying from the disease.
The previous high was 22,170 infections in 2013. The most number of deaths was 25, in 2005.
The NEA said: “If left unchecked, the current high Aedes aegypti mosquito population, coupled with the not insignificant number of dengue cases currently and the sizeable proportion of residents still working from home, would add to the dengue risk this year.”
Calling for greater vigilance against the mosquito-borne disease, the NEA said: “The population immunity for DenV-3 and DenV-4 is low, and more people are susceptible to transmission of the virus.
“This could result in a continued high risk of dengue transmission given the current moderate number of dengue cases and the relatively high Aedes aegypti mosquito population.”
DenV-3 was found in the cluster of 19 cases at the intersection of Upper Aljunied Road and MacPherson Road, which includes Jalan Muhibbah and Jalan Mulia.
DenV-4 was found in the Bedok North Street 3 cluster of 46 cases as well as the Gangsa Road cluster involving 21 cases.
These three clusters are among the top five dengue clusters today. The biggest of the 27 current clusters is in Tampines Place, involving 157 cases.
Last year, the NEA carried out about one million inspections for mosquito breeding and found 23,400 breeding habitats.
It promises to “adopt a high tempo of preventive inspections to remove mosquito breeding habitats, and further reduce the risk of dengue transmission”.