60 per cent increase in Aedes aegypti mosquito population in December 2016 compared to that in October 2016
Singapore, 19 January 2017 – While the current number of dengue cases is relatively low, the National Environment Agency (NEA) is forecasting that the number of cases could increase in the next few months, peaking in the middle of the year. A contributing factor and key concern is the higher Aedes aegyptimosquito population in the past month. NEA’s Gravitrap surveillance system has detected about 60 per cent more Aedes aegypti mosquitoes in December 2016 than in October 2016. If left unchecked, the high Aedes aegypti population may lead to a surge in dengue cases in 2017. NEA therefore urges all members of the public and stakeholders to stay vigilant, and work together as a community to stem dengue transmission.
2 Another factor which may lead to an increase in dengue cases is the high diversity of circulating dengue serotypes. The predominant serotype for 2017 thus remains uncertain, following the dominance of DENV-2 in much of 2016. Historically, a change in predominant dengue virus serotype has been followed by a spike in dengue cases. The Ministry of Health (MOH) and NEA will continue to monitor the situation closely.
Dengue Situation in 2016
3 In early 2016, NEA alerted the community of a possible outbreak following a switch in predominant serotype from DENV-1 to DENV-2. Despite an early surge in the number of cases early in 2016, the situation was brought under control and remained so for the rest of the year (see Figure 1). A combination of factors is assessed to have kept dengue cases in check last year, include strong community action, sustained and localised vector control efforts by all stakeholders, and weather conditions.
4 The ‘Do the Mozzie Wipeout’ Campaign 2016 was launched on 28 February 2016 – two months earlier than in typical years – to mobilise everyone to take immediate action to remove mosquito breeding habitats from the environment. Another concerted campaign was carried out in response to the Zika outbreak in August 2016. The Aedes aegypti mosquito population dropped by 80 per cent in the month following each of these two campaigns. Besides the community effort, the unusually warm weather in 2016 may also have contributed to the lower mosquito population, as studies have shown that very high temperatures can reduce the life span of mosquitoes.
Figure 1. Graph showing projected dengue cases versus actual dengue cases in 2016
5 In 2016, NEA conducted more than 1.2 million inspections, including 7,400 conducted on construction sites. NEA uncovered more than 16,000 instances of mosquito breeding habitats and about 3,900 households were fined for mosquito breeding. More than 660 Notices to Attend Court and over 60 Stop Work Orders were issued to construction sites. Over 60 court prosecutions were also taken against contractors for repeat offences. We will continue to take enforcement action against recalcitrant errant contractors and premises owners for mosquito breeding found on their premises.
Chinese New Year Advisory
6 As the Chinese New Year festive season approaches, residents are urged to prevent mosquito breeding, such as in ornamental plant containers, by practising the following steps:
- Turn over all water storage containers when not in use
- Change water in vases on alternate days
- Remove water from flower pot plates on alternate days
- Loosen hardened soil on alternate days.
7 Homeowners doing spring cleaning are also reminded to properly dispose of any refuse, including large furniture or household items, to avoid the discarded material from becoming unintentional mosquito breeding habitats. Those planning to go overseas for vacation during the upcoming holiday period should also mosquito-proof their homes before they travel. Residents can keep their neighbourhoods safe from dengue by taking these mosquito prevention measures:
- Cover all toilet bowls in the home
- Seal off the overflow pipe of the flushing cistern
- Cover and seal off all floor traps
- Add sand granular insecticide to areas where stagnant water cannot be easily removed, such as flower vases and toilet bowl collar
- Clear blockages and add Bti insecticide in roof gutters
- Turn over all water storage containers and wipe the rims dry
- Ask a relative or close friend to check your home regularly for stagnant water if you are going away for a long period of time
- Leave your contact details with your neighbours or the neighbourhood police post/centre so that you can be reached easily.
8 Persons infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see their doctors early to be diagnosed. The latest updates on the dengue situation can be found at the Stop Dengue Now Facebook page, www.dengue.gov.sg or the myENV app.
 Aedes aegypti is the main vector of dengue, and dwells in urban areas. The same mosquito vector also transmits Zika, Yellow fever and Chikungunya viruses. Hence, the preventive measures implemented will also help to prevent the transmission of these vector-borne diseases in Singapore.
 NEA has deployed 50,000 Gravitraps islandwide. The catches from these traps have helped NEA officers focus inspections and vector control activities on areas with high risk of dengue or Zika transmission.
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For more information, please contact us at 1800-CALL NEA (1800-2255 632) or submit your enquiries electronically via the Online Feedback Form or myENV mobile application.