40 per cent increase in Aedes aegypti mosquito population in December 2018 compared to that in December 2017

Singapore, 9 January 2019 – The number of dengue cases has increased over the past three consecutive weeks, with the first week of 2019 reporting 207 cases. A contributing factor and key concern is the higher Aedes aegypti [1} mosquito population detected in the community. NEA’s Gravitrap surveillance system has detected about 40 per cent more Aedes aegypti mosquitoes in December 2018, compared to that in December 2017 [2]. If left unchecked, the high Aedes aegypti mosquito population may lead to a surge in dengue cases in 2019. NEA therefore urges all members of the public and stakeholders to stay vigilant, and work together as a community to stem dengue transmission.

Dengue Situation in 2018 and Outlook for 2019

2          The total number of dengue cases reported in 2018 was 3,285, which is almost 20 per cent more than in 2017, but lower than the annual number of cases reported in the earlier outbreak years (Figure 1). However, the number of dengue cases has been increasing since the end of 2018. Contributing to this has been the upward trend in the Aedes aegypti mosquito population in the community, as registered by the Gravitrap surveillance system. A high Aedes mosquito population (together with other factors such as changes in the circulating virus type and herd immunity levels) are risk factors for the spread of dengue.

3          The predominant virus serotype has remained as Dengue serotype 2 since 2016. Although there is no signal for a major outbreak, the increased Aedes aegypti mosquito population in the community coupled with the high current number of dengue cases may lead to a surge in case numbers in 2019. Concerted community action and sustained vector control efforts are thus needed to prevent further escalation of the Aedes mosquito population, and a surge in the number of people becoming ill with dengue.

4          In 2018, NEA conducted about one million inspections for mosquito breeding, including about 9,000 checks at construction sites, and uncovered about 18,000 mosquito breeding habitats. As at November 2018 [3], about 4,100 households were fined for mosquito breeding. About 500 Notices to Attend Court and 40 Stop Work Orders were issued to construction sites. 25 court prosecutions were also made against contractors for repeat offences. NEA will continue with these inspection and enforcement efforts in 2019.  To safeguard public health, NEA will not hesitate to take contractors and residents to task for mosquito breeding found at their premises. In particular, NEA will take strong enforcement actions against recalcitrant errant premises owners.

5.         To keep dengue in check, NEA has commenced intensive source reduction exercise with our major stakeholders. Together with the members of the Inter-Agency Dengue Task Force [4], as well as all Town Councils, NEA will continue its efforts to remove potential mosquito breeding habitats from public areas and housing estates. Effective dengue prevention requires the vigilance and participation of everyone in the community. NEA strongly urges all members of the public to do their part to prevent and remove any breeding habitats of Aedes mosquitoes, and to remain vigilant in suppressing the Aedes mosquito population. These efforts will also contribute towards preventing the transmission of Zika and Chikungunya viruses.

Figure 1. Number of dengue cases from 2013 to 2018

Chinese New Year Advisory

5          Aedes mosquitoes can breed in clean stagnant water found in homes and other premises. As the Chinese New Year festive season approaches, homes and other premises are decorated with more ornamental plants. To pre-empt dengue, NEA has disseminated advisories to all nurseries ahead of the Chinese New Year period. All stakeholders are urged to prevent mosquito breeding and keep the mosquito population low, by practising the following steps to remove stagnant water:

• Turn the pail
• Tip the vase
• Flip the flowerpot plate
• Loosen the hardened soil
• Clear the roof gutter and place Bti insecticide inside

6          Homeowners doing spring cleaning are also reminded to properly dispose of any refuse, including large furniture or household items, to avoid the discarded materials from becoming unintentional mosquito breeding habitats.

7          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 the following mosquito prevention measures:

• Cover all toilet bowls in the home
• Seal the overflow pipe of the flushing cistern
• Cover and seal all floor traps
• Add sand granular insecticide to areas where stagnant water cannot be easily removed
• Clear blockages and place 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 easily contacted

8          Persons infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see doctors early to be diagnosed. The latest updates on the dengue situation can be found on NEA’s website, the Stop Dengue Now Facebook page, or the myENV app.

[1] 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.

[2] NEA has deployed 50,000 Gravitraps islandwide. The catches from these traps have helped NEA officers to optimise its resources by focusing inspections and vector control activities on areas with high risk of dengue or Zika transmission, leading to a more efficient and effective dengue surveillance programme.

[3] Provisional figures as at end Nov 2018. 

[4] The Inter-Agency Dengue Task Force comprises 28 stakeholders from the People, Public and Private (3P) sectors such as LTA, SLA, HDB, NParks to coordinate nationwide dengue control efforts.

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