Gravitrap surveillance system will be expanded to newly completed HDB blocks and landed housing estates, to target areas with high mosquito population
Singapore, 7 April 2019 – Mr. Masagos Zulkifli, Minister for the Environment and Water Resources, urged members of the public and stakeholders to stay vigilant and not let their guard down. Over 2,000 dengue cases have been reported in the first quarter of 2019, which is a more than three-fold increase from the approximately 600 dengue cases reported in the same period in 2018. Speaking at the main launch of the National Dengue Prevention Campaign 2019 at the North West District, Minister made the call for a concerted effort to step up our mosquito and dengue prevention efforts, to keep dengue transmission under control in the run up to the peak dengue season.
More cases expected
2 Even though the National Environment Agency (NEA) has detected seven per cent less Aedes aegypti mosquitoes in March 2019, compared to in March 2018, NEA has found from its Gravitrap surveillance system that the mosquito population still remains high. Our neighbouring countries have also reported sharp increases in dengue cases in recent months. The warmer months of June to October usually see higher transmission of dengue in Singapore, due to the accelerated development of the Aedes mosquito and the shorter incubation period of the dengue virus. NEA is thus expecting an increasing trend in dengue cases in the warmer months ahead, if we do not take active steps to keep the mosquito population in check.
Technology and Innovation in NEA’s dengue prevention efforts
3 NEA has deployed about 50,000 Gravitraps islandwide to monitor the Aedes mosquito population in Singapore. The data on mosquitoes caught in these traps has been used to guide NEA’s inspection efforts to focus on areas with high Aedes mosquito populations, thus enabling more efficient deployment of limited manpower resources. The traps have also been effective in helping NEA remove a large number of adult Aedes aegypti mosquitoes, including infected female mosquitoes. Through the deployment of the Gravitrap surveillance system, NEA was able to remove 21 per cent more mosquito breeding habitats last year, compared to 2017. This demonstrates the effectiveness of data analytics and continuous innovation in enhancing the efficacy of NEA’s vector control operations. Deployment of Gravitraps complements the efforts of the community, premises owners and other stakeholders in suppressing the mosquito population. Refer to Annex A for more information on the deployment of Gravitraps.
4 NEA intends to progressively deploy Gravitraps at newly completed HDB blocks, and expand the Gravitrap surveillance system to landed housing estates, in the second half of 2019. Currently, NEA officers routinely carry out inspections for mosquito breeding at landed housing estates, but this is highly resource intensive. By expanding the Gravitrap surveillance system to landed housing estates and newly completed HDB blocks, NEA will be able to gather more information on the adult mosquito population at each locality, enabling us to focus our limited resources in areas with high mosquito population. About 14,000 Gravitraps will be progressively deployed across the island in 2019, in addition to the 50,000 Gravitraps already in place.
5 NEA has embarked on the Phase 3 field study of Project Wolbachia – Singapore at the expanded Tampines West and Nee Soon East study sites, to determine if suppression of the urban Aedes aegypti mosquito population can be sustained in larger areas. In the recently concluded Phase 2 field study, 80 per cent and 70 per cent suppression of the urban Aedes aegypti mosquito population were achieved at the Nee Soon East and Tampines West study sites respectively. The results thus far show that a larger release site yields better results, and community effort in keeping the mosquito population low will enhance the effectiveness of Wolbachia technology. The Nee Soon East and Tampines West study sites have expanded by between 1.6 to 2.2 times, compared to the Phase 2 trial area. Even as NEA explores innovative solutions, such as Wolbachia technology, to complement NEA’s existing mosquito control efforts and suppress the urban Aedes aegypti mosquito population, community vigilance and action remains critical in our fight against dengue and Zika.
Concerted efforts to stem dengue transmission
6 NEA, together with the various agencies and other stakeholders represented in the Inter-Agency Dengue Task Force (IADTF), including Town Councils, have stepped up checks leading up to the traditional peak dengue season to remove potential mosquito breeding habitats in our public areas and housing estates. From January to March 2019, NEA conducted about 224,000 inspections, including about 1,800 inspections carried out at construction sites. NEA uncovered about 2,900 instances of mosquito breeding habitats.
7 NEA also continues to focus on areas with higher potential for dengue transmission such as construction sites. Through our concerted efforts, working with the Singapore Contractors Association Ltd (SCAL) and industry leaders, fewer construction sites have been found to be breeding mosquitoes, from 11 per cent in 2013 to four per cent in 2019. NEA takes strict enforcement action against construction sites found with mosquito breeding. From January to March 2019, NEA issued about 20 Notices to Attend Court and seven Stop Work Orders. In addition, two court prosecutions had also been taken against contractors for repeat offences.
8 While NEA explores more innovative ways to fight dengue, and exploits the potential of Wolbachia technology, source eradication of mosquito breeding habitats and spraying of insecticides where necessary to control the adult mosquito population, will continue to be our key strategies for dengue prevention in Singapore.
Community-led efforts are a key pillar
9 With a short breeding cycle of seven days, keeping the mosquito population in check requires the joint effort of every individual and stakeholder in the community to eradicate mosquito breeding habitats. Community-led efforts also play a key role in protecting our neighbourhoods from dengue and for tackling the problem collectively, whether preventing mosquitoes from breeding at home or at common spaces.
10 The campaign launch will be followed by islandwide outreach efforts across the five districts at different divisions, jointly led by the local Grassroots Advisers and leaders and NEA, working closely with Dengue Prevention Volunteers (DPVs). They will conduct patrols to check for potential mosquito breeding habitats at common areas around their neighbourhoods, and will conduct house visits to advise residents on common mosquito breeding habitats and to share dengue prevention tips. In particular, the campaign this year will focus on making residents aware that clean and stagnant water in their homes can be potential breeding habitats for mosquitoes. All it takes is a small amount of water the size of a 20-cent coin for mosquitoes to breed in, which would jeopardise the efforts that stakeholders have put in place to keep dengue transmission at bay.
11 To-date, NEA has trained more than 8,500 DPVs, comprising Grassroots Leaders, People’s Association Community Emergency and Response Teams (CERT) members, students, senior citizens and residents. These volunteers help to advise residents on common mosquito breeding habitats and dengue prevention tips during house visits and community events, and check for potential mosquito breeding habitats at common areas around their neighbourhoods. Refer to Annex B for the roles of residents and DPVs in preventing dengue.
12 The latest updates on the dengue situation can be found at NEA’s website, www.nea.gov.sg, Stop Dengue Now Facebook page, or the myENV app.
 The campaign was also concurrently launched by Mayor Ms Low Yen Ling together with Dr. Amy Khor, Senior Minister of State, Ministry of Environment and Water Resources at the South West District, Mayor Mr. Desmond Choo and Grassroots Adviser Mr. Chua Eng Leong at the North East District, Mayor Ms Denise Phua at the Central Singapore District, and Grassroots Adviser Mr. Tan Chuan-Jin at the South East District.
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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.
1 The Gravitrap, developed by the National Environment Agency’s (NEA) Environmental Health Institute (EHI), is designed to attract and trap female Aedes mosquitoes that are looking for sites to lay their eggs. Such mosquitoes are not looking for a blood meal and hence will not bite people. Female mosquitoes attempting to lay their eggs in these containers will be captured and thus prevented from biting other people subsequently. The Gravitrap also traps and prevents the emergence of any mosquitoes from eggs that are laid in the trap.
2 Since 2017, NEA has deployed about 50,000 Gravitraps in HDB blocks to monitor the Aedes population in Singapore. When deployed across an area, Gravitraps provide an indication of the Aedes mosquito population in the vicinity. Knowing which Gravitraps are capturing these mosquitoes helps NEA prioritise our resources, by directing our officers to search for and destroy the mosquito breeding habitats at locations with higher Aedes mosquito populations. NEA was able to remove 21 per cent more breeding habitats last year, compared to in 2017. This was achieved through our targeted inspections, which were guided by our Gravitrap surveillance system.
Improvement and deployment of additional Gravitraps
3 With climate change and accelerated urbanisation, there is a need to continually innovate and design sustainable solutions to deal with environmental challenges. A study conducted by NEA revealed that adding covers to the Gravitraps makes them relatively more attractive to mosquitoes than non-covered traps. The covers minimise the exposure of the sticky lining within the traps to external elements like dust, thus allowing the sticky lining to remain effective for a longer period of time. This also means that the sticky linings can be changed less frequently, whilst not compromising the attractiveness of the traps to mosquitoes. Hence, NEA will be incorporating covers to our existing and new Gravitraps. This will help to enhance data collection of the mosquito population, and lead to more effective Aedes mosquito surveillance and better dengue control. A picture of the covered Gravitrap can be found below.
4 Additionally, NEA intends to progressively deploy Gravitraps at newly completed HDB blocks, and expand the Gravitrap surveillance system to landed housing estates in the second half of 2019. Currently, NEA officers routinely carry out inspection for mosquito breeding habitats at landed housing estates, but this is resource intensive. By expanding the Gravitrap surveillance system to landed housing estates and newly completed HDB blocks, NEA will be able to obtain more information on the adult mosquito population at each locality, allowing us to focus our limited resources in areas with high mosquito populations. About 14,000 Gravitraps will be progressively deployed across the island in 2019, in addition to the 50,000 already in place.
5 Gravitraps are usually deployed along the common corridors of residential premises. NEA officers will check and maintain the Gravitraps regularly, to ensure that they are functioning properly. If the Gravitraps are misplaced or toppled, this disrupts our surveillance network and could cause our officers to prioritise search for mosquito breeding habitats at wrong areas, resulting in delays in tackling the mosquito situation. We therefore seek the cooperation of the public not to remove or tamper with the Gravitraps. If members of the public come across Gravitraps that have been toppled, please contact 1800-2255-632 so that our officers can follow up.
Fig 1. Image showing a Gravitrap and its cover
Roles of Residents and Dengue Prevention Volunteers in Preventing Dengue
- Practise the 5-step Mozzie Wipeout regularly
- Apply insect repellent and wear long-sleeved shirts and long pants
- Spray insecticide in dark corners of the home, such as under the bed and sofa, and behind curtains
- Cover toilet bowls, sinks and gully traps and ensure there is no stagnant water at home, before leaving for vacation
- Seek medical treatment early if feeling unwell
- Participate in dengue prevention campaigns in neighbourhoods
Dengue Prevention Volunteers
- Dengue Prevention Volunteers complement NEA’s outreach efforts, in helping to disseminate the knowledge of dengue prevention among residents and the community, so that they can carry out these efforts on a sustained basis.
- Dengue Prevention Volunteers help to:
- Reach out to their family, friends and neighbours to incorporate dengue prevention steps in their daily routines.
- Advise residents on potential mosquito breeding habitats during house visits and community events, and remind residents to remove stagnant water in their homes.
- Share information about mosquitoes, including the characteristics of Aedes mosquitoes, symptoms of dengue fever, how dengue is transmitted, and how residents can look after themselves to stem dengue transmission:
- Advise residents to apply insect repellent to protect themselves, especially for those living in dengue cluster areas.
- Encourage residents showing symptoms suggestive of dengue to see their GPs early to be diagnosed.
- Educate residents infected with dengue to protect themselves from mosquito bites, by applying repellent and wearing long-sleeved tops and long pants to stem further dengue transmission.
- Check for potential mosquito breeding habitats in common areas around their neighbourhoods.
- Encourage fellow residents to participate in dengue prevention activities in their neighbourhoods.
- NEA welcomes more volunteers from the community to join as Dengue Prevention Volunteers. Interested members of the public can do so by contacting our hotline at 1800 2255-632 or signing up at www.cgs.sg/volunteer.