More mozzie-busters are being sent this weekend to the dengue-riddled part of Bukit Batok, which has become the largest single cluster recorded in the last nine years, to try and get the situation under control.

Forty environmental health officers from the National Environment Agency (NEA) will be on yet another seek-and-destroy mission for Aedes mosquito breeding in the area bound by Bukit Batok streets 31, 32 and 34, which has seen 77 cases so far.

Dengue has been actively transmitted in the area for 58 days.

This is the third time NEA is sending its officers to the stubborn dengue hot spot, one of five in Bukit Batok right now, said Mr S. Satish Appoo, director of the NEA's Environmental Health Department. The first two times, 10 officers went in, and the second time, 20 did.

Then, 26 indoor and seven outdoor breeding spots were uncovered, and profuse breeding was found in places like vases, pails and roof gutters.

So far this year, Bukit Batok has seen a record of 241 cases, with a total of 21 dengue clusters identified.

One reason for the unusually high level of dengue in the area: Its population is more susceptible because dengue has only recently moved into the western parts of the island, so fewer people have immunity, explained Mr Appoo.

In the 1970s, the Aedes aegypti, the primary culprit, was confined to the east, he said, adding that its eggs - which, when dried, can last for half a year - could have been brought over when people moved homes.

Still, before 2004, each dengue season saw fewer than 30 cases. The numbers started picking up only after that: 88 cases in 2004, 203 in 2005 and 122 last year.

Yet another factor: Aedes aegypti numbers in the area have exploded in the last four years, jumping from 1 per cent of the area's Aedes mosquito population in 2003 to 66 per cent this year, said NEA.

While the Aedes albopictus can also cause dengue, outbreaks are associated with the Aedes aegypti because they bite more than one person. So more Aedes aegypti mosquitoes mean higher risk for a population with low immunity.

'It has all the conditions making it prime for an outbreak. And we can't control the immunity, so we have to control the vector,'' Mr Appoo added.

But each time the mozzie-busters return, they find new breeding sites and more eggs that may have already matured, he said.

'This has been going on for too long...If even a small number disregard the message, they put the entire community at risk,'' he said.

But despite the roadshows and pamphlets distributed, and representatives from the town council and grassroots leaders working the ground, some are clearly not getting the message.

He said: 'The only way to eliminate dengue is to stop the breeding...It is in the hands of the public.'