The NEA mounted its annual pre-emptive strike two months earlier this year, in January instead of March.

The sweep of potentially productive mosquito breeding sites in housing estates was completed last month, which is when this phase of the mosquito war usually starts.

More than 400 NEA officers combed every drain and water tank in HDB estates, on top of the routine surveillance and extermination of breeding sites by the town councils.

Their mission: to seek out and destroy as many breeding sites as possible before the onset of warmer mid-year weather, which puts mosquitoes in breeding mode.

At around this time last year, which was warmer, the number of people down with dengue had shot past 100 cases a week.

Singapore, emerging from the coolest March in two decades this year, is already starting to see a rise in the number of dengue patients.

Last week, 97 people were infected, 20 more than in the previous week.

Read the full story in Tuesday's edition of The Straits Times.