Source: Asia Pacific Region 2 – Singapore
Collective efforts of all stakeholders have helped to bring this year’s dengue outbreak under control, with weekly cases since the second half of November below the number of weekly dengue cases at the start of 2020. With mosquito population still high in some areas and many residents still working from home, NEA urges continued vigilance in eradicating stagnant water to prevent mosquito breeding. NEA will continue to adopt a high tempo of preventive inspections to further slow down dengue transmission during this year-end period, to lower the risk of another dengue outbreak in 2021.
Singapore, 18 December 2020 – As of 17 December 2020, there have been 34,844 reported dengue cases this year, with 228 cases reported last week. The latest weekly dengue case number is about seven times lower than the peak of 1,792 seen in July this year. Besides being the lowest weekly case number this year, last week’s figure is also the fourth successive week where case numbers have gone below 300. Due to a confluence of factors, some of them COVID-19 related, 2020 will end as the historic dengue outbreak year. The year started with a high of 303 weekly cases, and it was only in the third week of November that the weekly case count dropped below 300. This progress was made possible through sustained outreach and intensive dengue control efforts by the Inter-Agency Dengue Task Force (IADTF), Town Councils and the National Environment Agency (NEA), throughout most of this year.
2 The year started with high weekly dengue cases of between 300 – 400, and the relative dominance of the more unusual dengue virus serotype (DENV-3) in the first four months of the year. Weekly cases rose sharply in May 2020, shortly after the start of the Circuit Breaker, and eventually peaked in July 2020. In response, our community stakeholders rallied together to fight dengue, despite the exceptional challenges posed by the COVID-19 outbreak and the unprecedented high number of dengue cases. These efforts included residents checking their homes frequently for potential mosquito breeding habitats, and using insect repellent and insecticides to protect themselves and loved ones, which will also help to break the dengue transmission chain. Town Councils and stakeholders were also mobilised to step up inspections and vector control operations in the common areas of estates, and worked closely with Grassroots Leaders and community volunteers to reach out to residents on dengue prevention and control efforts. Together, these efforts have been critical in bringing down dengue transmission from August onwards (refer to ANNEX A for factors leading to dengue surge and recap of NEA’s enhanced dengue control efforts).
3 However, the present weekly case number of between 200 and 300 is still relatively high for this time of the year. While this is below the weekly case number last year (2019), it is still about three times the average number of cases reported in the preceding three years (2016-2018), which saw fairly low dengue case numbers. Two other indicators that bear watching are the 20 per cent increase in adult Aedes aegypti mosquito population in November – there are currently over 230 residential areas with high Aedes aegypti mosquito population, and the relatively higher proportion of DENV-3 and DENV-4 serotype cases which are less common in Singapore. We therefore urge everyone to stay vigilant against the dengue threat, and to sustain the good efforts and efforts so far in stemming dengue transmission.
4 “NEA would like to thank all our community stakeholders who have played a key role in leading dengue prevention efforts during this historic dengue outbreak year, in spite of the exceptional challenges posed by COVID-19. The steady decline in weekly dengue case numbers since August shows how far we have come together in fighting dengue. Community support will always be an important part of our fight against dengue, and we must continue to keep up our efforts to eliminate mosquito breeding habitats and take steps to protect ourselves from dengue”, said Mr Chew Ming Fai, Deputy Chief Executive Officer and Director-General of Public Health, NEA.
Dengue Situation in 2020
5 57 dengue clusters have been reported as of 17 December 2020, a decrease of 7 clusters from the previous week. Overall, NEA has closed about 98 per cent, or 3,003 of 3,060, of the dengue clusters notified since the beginning of this year. However, large dengue clusters remain at Tampines Street 11, Geylang Road, Bukit Batok Street 21 and Admiralty Drive, where intensive vector control operations are ongoing. NEA is also focusing on clusters with the less common dengue virus serotypes (DENV-3 and DENV-4), and has been working closely with key stakeholders in the IADTF, including Town Councils, on sustained environmental management efforts.
6 Despite the recent decline in dengue cases, NEA and its IADTF partners are not letting their guard down, as the Aedes aegypti mosquito population remains high in some areas in Singapore. NEA will continue to adopt a high tempo of preventive inspections to remove mosquito breeding habitats and further slow down dengue transmission. In addition to efforts in dengue cluster areas, NEA will also be focusing on areas with high Aedes aegypti mosquito population that are adjacent to dengue clusters or have not experienced dengue transmission this year. Construction sites and industrial premises in close proximity to residential areas will also continue to be areas of focus.
7 NEA has been working closely with Grassroots Advisers and community volunteers, to reach out to and advise residents on dengue prevention efforts. Between January and November 2020 , NEA conducted about 954,000 inspections for mosquito breeding islandwide, including about 6,900 checks at construction sites, and uncovered about 21,500 mosquito breeding habitats. During the same period, 7,060 enforcement actions have been taken against owners of premises for mosquito breeding. About 370 summonses and 34 Stop Work Orders were issued to construction sites, and 18 contractors were charged in court for repeat offences. Since the implementation of the heavier penalties against homes from 15 July 2020, about 260 of NEA’s subsequent inspections at residential premises were found with repeated mosquito breeding. 26 out of these 260 inspections also yielded multiple mosquito breeding habitats.
Figure 1. Number of dengue cases from 2016 to 2020 (as at Epidemiological week (E-week) 50)
Mosquito-Proof Homes Before Going On Staycation
8 As there is a higher tendency for water to remain stagnant in unused premises, those planning to go on staycation spanning a few days should take the following extra steps to prevent mosquito breeding:
• Cover all toilet bowls in your home, and seal off overflow pipes of the flushing cisterns
• Cover all floor traps
• Add Bti to places where mosquitoes could potentially breed, and places where stagnant water cannot be removed
• Clear debris and blockages, and place Bti insecticide in roof gutters and drains within compounds
• Turn over all water storage containers and wipe the rims dry
• Ensure that flower pots, plates and trays do not collect water, after watering your plants
• Ask a relative or close friend to check your home regularly for stagnant water, if you will not be around 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 reached if needed
9 It is critical that stakeholders and the community continue to work together with NEA, to arrest the high Aedes aegypti mosquito population in the community and break the disease transmission. The risk of dengue is real given that the virus is endemic in Singapore, the historic dengue outbreak seen this year, and with a sizeable proportion of residents still working from home. Residents, especially those residing in dengue cluster areas, should do their part and carry out the three protective actions against dengue – spray insecticide in dark corners around the house, apply insect repellent regularly, and wear long-sleeve tops and long pants. Repellents containing DEET (N,N-diethyl-m-toluamide), picaridin or IR3535 as the active ingredient are the most effective in repelling mosquitoes. The community should also continue to do the Mozzie Wipeout at least once a week, and ensure that their homes, premises and immediate surroundings are free from stagnant water.
 Provisional figures for inspections, mosquito breeding and enforcement, as of 9 December 2020.
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Factsheet on Factors Leading to Dengue Surge and Recap of NEA’s Enhanced Dengue Control Efforts in 2020
Factors leading to the dengue surge
- A confluence of factors contributed to the surge in dengue cases this year. First, an increase in the less common Dengue virus serotype 3 (DENV-3) since the beginning of this year. This serotype is uncommon in Singapore, which means that there is low immunity in our population. This contributed to the unusually high number of weekly cases.
- Second, there has been an increase in the population of the primary mosquito vector, Aedes aegypti, since 2019, as revealed by NEA’s Gravitrap surveillance system.
- While the two factors were driving the dengue situation in the first quarter of the year, signalling an imminent large dengue outbreak, the situation was exacerbated by the COVID-19 situation and the measures against COVID-19. Our analysis estimated 50 per cent more dengue infections during the Circuit Breaker period, compared to what we would expect for that period in 2020.
- Female Aedes aegypti mosquitoes are day-biters and harbour within the indoor environment. The work-from-home arrangement to allow social distancing has led to most people working from naturally ventilated homes, rather than offices, shops and factories. This increased the probability of contact between Aedes aegypti mosquitoes and humans, and would have contributed to the increase in dengue cases.
- At the same time, the mosquito population continued to rise in the middle of the year. The impact of the suspension of construction sites is seen in the three-fold increase in the proportion of mosquito breeding found in construction sites from April to June, compared to from January to March.
- At home, more mosquito breeding was also found, perhaps due to the challenges faced by residents in juggling working from home, higher housekeeping load, and home schooling of children.
- Other factors at play during the Circuit Breaker period could also have compounded the dengue situation. These include the reduction in some landscaping works due to manpower shortages, and cessation of the bulk of construction activities, which would have hampered good housekeeping at construction sites.
NEA’s enhanced dengue control efforts
- NEA takes a multi-pronged approach to dengue control, comprising vector control measures, stakeholder engagement, as well as community mobilisation and public communications. In anticipation of the surge this year, several enhanced efforts were undertaken this year and are still ongoing.
- NEA completed roll-out of the Gravitrap surveillance system to landed estates in early 2020. This enhanced surveillance complements the Gravitrap surveillance data collected from HDB estates, and has enabled NEA to conduct more targeted and effective inspections and vector control operations.
- Since end-2019, NEA has also made available information on areas with higher Aedes aegypti mosquito population on the myENV app and website. This is to increase the awareness of residents living in these areas, so that they can take preemptive steps with source reduction to bring down the mosquito population. Mosquito population is a lead indicator of a dengue cluster, and by putting out this information, NEA aims to equip residents with information that they can act on, to take proactive steps to prevent dengue.
- NEA convened the IADTF meeting in January, with six more meetings carried out this year, to collectively intensify source reduction efforts and sustain good environmental management within members’ premises.
- Responding to the COVID-19 situation in dormitories, NEA stepped up inspections at dormitories (including decanted ones) and Construction Temporary Quarters (CTQ), to ensure stringent mosquito control measures were put in place and sustained by operators.
- As visual cues within neighbourhoods have been found to be effective in creating awareness, NEA has expanded the number of dengue alert banners displayed at neighbourhood precincts of dengue cluster areas, and brought this awareness closer to homes by putting up dengue posters at the individual HDB block level. SMS blasts have also been sent to targeted dengue cluster areas, to remind residents to check their homes for stagnant water and Do the Mozzie Wipeout regularly.
- NEA has been stepping up outreach efforts at dengue cluster areas, including conducting house visits and distributing mosquito repellent and outreach materials to residents. Volunteers and poster walkers have also been deployed at town centres at dengue cluster areas, to augment outreach efforts.
- In May 2020, NEA worked with the Ministry of Health, Polyclinics and General Practitioners, to provide over 300,000 bottles of mosquito repellent for distribution to patients who are suspected to have dengue. This aimed to help break the dengue transmission chain, especially in dengue cluster areas or where the mosquito population is high. The messages on spraying aerosol insecticide in dark corners of the home have also been enhanced, to educate residents on how to protect themselves and their loved ones.
- In July 2020, NEA worked with all Town Councils to step up inspections and vector control operations in common areas, to ensure that drains are well maintained, common areas are kept litter-free, and stagnant water is removed or treated. This was part of a two-week intensive vector control effort to help break the dengue transmission chain. Town Councils were also urged to work with NEA to coordinate chemical treatment, such as fogging, misting and larviciding, in dengue cluster areas, to bring down the adult mosquito population.
- NEA continues to work closely with Grassroots Advisers and Leaders and community volunteers, to reach out to more residents to advise them to get rid of mosquito breeding habitats at home, and on the importance of applying repellent and spraying insecticide regularly.
- Since 15 July 2020, NEA has also imposed heavier penalties for households found with repeated mosquito breeding offences, multiple mosquito breeding habitats detected during a single inspection, and mosquito breeding detected after having received a legal notice from NEA. Enforcement has also been tightened for construction sites and Town Councils.
- With the high weekly dengue case numbers and the large number of households located in dengue cluster areas islandwide, NEA worked with partners to distribute mosquito repellent and educational materials to residents in dengue cluster areas, to protect themselves and their loved ones against dengue. This effort was also expanded to schools located in dengue cluster areas with high numbers of cases.
- To keep the awareness of dengue high and sustain preventive action amongst the community, NEA worked with Grassroots Leaders to step up dengue prevention efforts at landed residential estates during the year-end holiday season. This included distributing Mozzie-Proof Your Home tool kits to close to 75,000 landed residential homes in Singapore.