A 79-year-old man died of dengue fever on Saturday after being admitted to Tan Tock Seng Hospital last Wednesday.

He is believed to be the third person to have died of the disease in Singapore this year.

The other two victims were a 53-year-old woman from China in February and a 60-year-old woman from India who was visiting her son here in September.

It is not known whether he suffered from other conditions that may have affected his immune system and made him more vulnerable to the disease.

Although the man's home in Toa Payoh Lorong 8 is not known to be in an active dengue cluster, officers from the National Environment Agency (NEA) are conducting efforts to kill adult mosquitoes as well as destroy potential breeding sites in the area.

The NEA and the Ministry of Health (MOH) have both advised members of the public to allow NEA officers into their homes to search for potential mosquito-breeding sites and spray insecticide.

They also said that warmer conditions caused by El Niño could result in shorter breeding periods for Aedes mosquitoes and shorter incubation times for the dengue virus.

As of Friday, there were 39 active dengue clusters.

The largest, in the area stretching from Tampines Street 81 to Tampines Street 91, had 42 reported cases of the disease in the last two weeks.

There were 254 dengue cases between Nov 15 and 24, according to the NEA website.

The NEA and MOH advised members of the public to practise the "five-step mozzie wipeout", referring to actions to remove stagnant water to prevent mosquito breeding.

These include inverting buckets and plant pot plates, and regularly changing water in vases.

They also said that those infected with dengue should apply mosquito repellent to prevent mosquitoes from biting them and infecting others, and that those with symptoms of the disease should consult a doctor.