Dengue infections this year have surged past the 10,000 mark this week. The 872 cases last week are more than double the 391 cases just five weeks ago.
The National Environment Agency (NEA) said on its website: "This is the highest number of cases in the first five months of the year since 2013, the largest outbreak year recorded in Singapore's recent history."
In 2013, 22,170 people were infected and eight died. So far this year, 12 people aged between 56 and 80 have died of dengue.
The highest number of dengue deaths was in 2005, when 25 people died. Last year, 20 people died.
NEA warned that the hot and wet conditions suitable for the growth of the Aedes mosquito population are likely to last till October.
Dengue is spread through mosquito bites and not from person to person. But people with dengue are urged to use mosquito repellent to prevent themselves from being bitten by mosquitoes, which would then pass the virus to other people.
There are now 190 active dengue clusters. The biggest is in the Woodleigh area along Upper Serangoon Road, with 200 people infected, 33 within the past fortnight. It is one of five large clusters with more than 100 infected. There are 59 high-risk clusters with 10 or more people located within 150m of one another who were infected within a fortnight of one another.
Mr Sitoh Yih Pin, MP for the area, said: "Since the first case in Wood-leigh around early April, we have been working tirelessly with NEA."
This involves NEA officers stepping up enforcement in the common areas and construction sites, and visiting almost all the households in the vicinity.
The citizens' consultative committee has distributed insecticides and repellents to all households, said Mr Sitoh, adding: "We hope to resolve this as soon as possible."
Associate Professor Alex Cook, an epidemiologist at the NUS Saw Swee Hock School of Public Health, said experts had looked at whether the Covid-19 circuit breaker measures in April and May caused the jump in infections, as more people were staying at home, but found this was not the case.
The increase follows the normal seasonal patterns. But this year, because of the change in the dominant strain of the dengue virus, fewer people would be immune.
This strain, DenV-3, has not been dominant in the past three decades. But it accounted for more than 40 per cent of infections in the first quarter of the year and now shares dominance with DenV-2.
People who have been infected are protected against only that strain of the virus, and not against the other three dengue strains.
Prof Cook said: "For those of us who are spending more time at home due to the ongoing restrictions, it would be wise to take extra precautions, especially removing stagnant water from around the household and common corridor.
"We really want to avoid having the hospitals stretched by two outbreaks at the same time."
Roughly one in five people diagnosed with dengue is sick enough to require hospital care.
Dengue causes nausea and vomiting, aches and pain in the muscles, joints and bones, and behind the eyes, and a red rash. Some people might get the more serious dengue haemorrhagic fever that causes bleeding from the nose or gums, as well as internal bleeding that shows up as blood in the stools or vomit.
