SINGAPORE- The number of dengue cases so far this year has fallen by almost half compared to the same period last year but the National Environment Agency (NEA) has urged Singaporeans to remain vigilant against the dengue threat.

Between January and May this year, a total of 3,309 dengue cases were reported - 45 per cent lower than last year's figure of 6,015 during the same period, said the NEA.

However, the NEA has warned that dengue cases may rise in the next few months. This is due to the traditional warmer months of June to October which could pose risk of higher transmission of dengue due to faster breeding and maturation cycles for the Aedes mosquitoes.

There has also been a proportionately higher number of dengue cases detected with dengue virus serotype DENV-2 compared to DENV-1, which may lead to a spike in dengue cases afterwards.

The DENV-1 virus has been the dominant circulating virus since March 2013. However, the proportion of DENV-2 cases has risen from 18.3 per cent in 2014 to approximately 44 per cent in mid-May 2015.

"Historically, a change in the predominant dengue serotype has been followed by a spike in dengue cases. The last serotype switch, from DENV-2 to DENV-1, took place in March 2013 accompanied by a sharp dengue outbreak that year," said the agency in a press release.

NEA also reminded all stakeholders to ensure that their premises are free of mosquito breeding and "step up their efforts to stem dengue transmission, regardless of the circulating virus serotype".

Of the over 6,000 mosquito breeding habitats which were destroyed through the NEA's inspections as of mid-May this year, the majority of them were found in homes.

Mosquito breeding was also found in 7.4 per cent of the more than 4,000 inspections conducted at construction sites, said the NEA.