SINGAPORE — It was not so much the increase in mosquito breeding spots, but rather its coupling with the population’s low herd immunity to the new variant of dengue that led to the worst dengue outbreak here.

Minister for the Environment and Water Resources Vivian Balakrishnan said this yesterday, as he addressed questions from Members of Parliament (MPs) about the effectiveness of dengue- control measures during the debate on the ministry’s budget

The National Environment Agency (NEA) will deploy new tools to fight against dengue. For instance, the use of Gravitrap surveillance systems — cylindrical devices with sticky surfaces to trap Aedes mosquitoes — deployed in Bukit Panjang and Clementi will be extended to other parts of the island.

Dr Balakrishnan said the NEA found an increase of about 10 per cent in the number of mosquito breeding sites, a figure that was “not all that significant”. “But this 10 per cent increase in breeding, superimposed with the new virus which we have very low immunity (against), led to this explosive situation that we have now,” he said.

Last year, dengue cases hit a historic high of 22,170 — 50 per cent more than the previous peak in 2005. Since the start of this year, there have been 3,147 cases.

Dr Balakrishnan agreed with the MPs that vaccines would offer a long-term solution, but as of now, there are no vaccines for all four serotypes of dengue, which is why the authorities are focusing on “source eradication”.

He highlighted construction sites as an area of concern — mosquito breeding sites were found at 10 per cent of the 12,000 inspections conducted at constructions sites last year. The authorities issued 55 stop-work orders and 26 contractors were taken to court and fined S$3.5 million.

“We need to strengthen our housekeeping and our environmental management on-site. We will not hesitate to take strong and tough action because 10 per cent is an unacceptably high rate for breeding,” he said.

While the figure has since dropped to 4 per cent, Dr Balakrishnan added there is room for improvement. Siau Ming En