Update on Dengue Cases and Measures to Contain Its Spread

Ms Joan Pereira asked the Minister for the Environment and Water Resources whether the Ministry will consider expediting the trial of Project Wolbachia in the top dengue clusters given the high success rate of this project in eradicating the Aedes mosquito populations.

Ms Joan Pereira asked the Minister for the Environment and Water Resources whether the NEA can consider allocating more resources to step up efforts in eradicating mosquito breeding habitats through surveillance and inspections.

Mr Dennis Tan Lip Fong asked the Minister for the Environment and Water Resources what are the reasons for the continuing increase in the number of dengue cases this year despite the increase in mitigation measures such as fogging and inspections that have been taken in reported dengue clusters.

Mr Ang Hin Kee asked the Minister for the Environment and Water Resources (a) whether the measures taken to reduce the instances of dengue fever have been yielding results; and (b) whether there are other reasons for the high number of cases so far.

Thank you. Based on NEA's surveillance, the surge in dengue cases this year is attributable to three key factors – an increase in mosquito population; the relatively warmer weather; and lower herd immunity in our population.

NEA's gravitrap surveillance system has shown an increase in the Aedes aegypti mosquito population by almost three times, since the last major dengue outbreak in 2013. This persistently high Aedes aegypti mosquito population increases the risk of transmission of the dengue virus. In addition, the mean temperature for the first half of this year was 0.7 degrees higher than the same period last year. Warmer temperatures result in higher transmission of dengue due to the accelerated development of the Aedes mosquito and shorter incubation period of the dengue virus. Due to our past successes in dengue prevention, the proportion of adults who have had dengue before has progressively decreased from 59% in 2004, to 51% in 2009, and 41% in 2017. This results, however, in lower herd immunity among our population, and a large proportion of Singapore's resident population remains susceptible to dengue.

NEA, together with agencies in the Inter-Agency Dengue Task Force and Town Councils, have stepped up housekeeping measures and inspections of common areas to eliminate potential breeding areas. In the first six months of the year, NEA has conducted more than 442,000 inspections island-wide and uncovered about 8,200 mosquito breeding habitats. Sixty percent of the breeding habitats detected were found in residential premises. If we look at dengue clusters, the proportion of breeding habitats detected in residential premises is even higher at 70%. This points to an urgent need for home and premises owners to step up their efforts to eradicate mosquito breeding habitats. NEA will enforce against premises owners found with mosquito breeding and has taken about 1,200 enforcement actions against households between January and June.

Since the launch of the National Dengue Prevention Campaign in April, 89 divisions across Singapore have organised more than 1,000 dengue prevention events and activities. Mayors, grassroots advisers, community leaders and dengue prevention volunteers have been visiting homes to share dengue prevention tips, including information on how to identify potential mosquito breeding habitats. To heighten the public's awareness and vigilance against mosquito breeding and dengue, dengue cluster alert banners, posters and notices have also been strategically placed around the estate in dengue cluster areas. Poster walkers have been deployed and dengue prevention advertorials have been displayed at high footfall areas within clusters. NEA has also reached out to the public through TV and radio commercials, as well as digital and social media platforms such as Facebook and Instagram.

We are seeing positive outcomes from these collective efforts. As of 24 August, we have closed 863 of the 1,021 clusters formed in 2019. This weekly number of dengue cases has also come down from a high of 664 cases in the second week of July to the current 478 cases in the third week of August. Some of the largest clusters in Woodlands, Upper Thomson, Chai Chee and Pasir Ris, have closed. I would like to take this opportunity to thank all our stakeholders, including the grassroots advisers, grassroots leaders, dengue prevention volunteers, Town Councils and residents, for your efforts.

NEA will continue to work with our partners to enhance the efforts in dengue control. From the second half of 2019, NEA will progressively deploy an additional 14,000 Gravitraps to new HDB blocks and landed estates. This will augment NEA's current network of 50,000 Gravitraps, and enhance our surveillance capabilities. The Gravitrap surveillance system allows NEA to prioritise its resources and deploy officers to focus on areas with high mosquito population.

In addition, since 25 August, NEA has partnered with People's Association (PA) to step up dengue outreach. Five thousand volunteers from PA grassroots organisations and Community Emergency and Response Teams (CERTs) will work hand in hand with dengue prevention volunteers to conduct house visits and distribute dengue prevention leaflets.

Another new initiative by NEA is the sharing of information on areas with relatively higher Aedes aegypti adult mosquito population on its webpage, to facilitate targeted action by key stakeholders, community partners and residents. The information aims to increase awareness of dengue risk in areas with high mosquito population which might not yet be dengue clusters, so that stakeholders can pre-emptively take measures to reduce potential mosquito breeding habitats and avoid the formation of new dengue clusters.

While the results from Project Wolbachia field studies have shown promise, the Wolbachia technology has only been tested in small study sites in Singapore, and remains under research and development. It is important for NEA to evaluate the technology rigorously before deploying it on a larger scale. NEA's approach to Project Wolbachia is aligned with the World Health Organization's (WHO) and International Atomic Energy Agency's guidelines on developing sterile insect technologies using a phased approach.

Each phase of Project Wolbachia has a clearly defined objective, to progress the study and evaluate the technology systematically. The project is now in Phase 3, which aims to determine if the Aedes aegypti population suppression achieved thus far can be sustained in larger areas. The release area covers 84 blocks in Yishun and 60 blocks in Tampines and is 3.7 times larger than the release area when Wolbachia first started. It also focuses on the development of automation for male Wolbachia-Aedes mosquito production and release, to ensure scalability of the technology. As field studies require prior systematic design, preparation and historical data for comparison, they are not suited for reacting to current dengue clusters, which are very dynamic.

Wolbachia technology is also not a silver bullet. It will not replace the community's efforts to ensure good house-keeping, which is still needed to keep our homes and estates free from mosquitoes and dengue. Comprehensive mosquito surveillance, source eradication of mosquito breeding habitats, and spraying of insecticide where necessary to control the adult mosquito population, continue to be Singapore's key strategies for dengue prevention and control.

Mr Speaker, we are still in the peak dengue season, which stretches from June to October. The region around us is similarly seeing an upsurge in dengue cases this year. We need to remain vigilant, and continue to work as a community to suppress the Aedes mosquito population and keep dengue cases in check. I urge everyone to join in the collective effort to stop the dengue transmission cycle, by regularly doing the five-step Mozzie Wipeout and to remind your family members, friends and neighbours to remove stagnant water from within and around their homes.

Mr Speaker, there was a death due to dengue in my ward this year. Many of my residents are understandably very concerned and many of my residents have asked why fogging is being carried out infrequently as opposed to the past. I would like to ask the Minister if he can clarify, whether fogging is still an effective method to combat the Aedes mosquitoe and if Ministry will continue to use it as a tool.

As I mentioned just now, in areas where there are higher incidences of dengue fever, 70% of the breeding is found in homes. So, even if we carried out more fogging, residents will usually close their windows anyway. Therefore, the best way to prevent dengue from proliferating is to destroy their habitats and most of them are within homes. But do we do fogging? Yes, we can and we must, to kill the adult mosquitoes outside. There is no silver bullet in whichever method we choose and we cannot just use one method to stop this problem.

Speaker, supplementary question for the Minister. Earlier, he talked about lower herd immunity and attributed it to the fact that the dengue prevention efforts of the past years have shown some effectiveness. I would like to ask him whether there has been observed to be a change in the serotypes, the strain of dengue that is now predominant in Singapore, and whether that contributes to the higher incidence of cases?

There is no known significant switch in serotype of dengue strains found in Singapore. So, as I have mentioned, the three factors, among which is the low herd immunity, is one major factor which is causing the spike in the number of dengue cases in Singapore, rather than serotype switch.

I have two follow-up questions. First, is there any discernible difference in terms of breeding sites and residents contracting dengue for private estates and HDB estates? Secondly, a lot of residents and Singaporeans travel overseas. Are there incidents of them contracting dengue overseas because they let their guards down or they are not aware that the regions that they visit are also experiencing a dengue outbreak?

There are clear differences between breeding places in private estates and public housing. For public housing, some of them are found in common areas and the Town Councils must and should take all precautions possible to prevent breeding and mosquitoes. Some of these places are really hard to access. Whereas for private housing, most of the breeding places, in addition to being found within homes, are also found in their gardens, usually in pots which are not probably treated or pots which collect water.

For cases of dengue contracted overseas, as I had mentioned, our region is now suffering from a spike in the number of dengue cases. Therefore, as we travel, please take the necessary precautions, put on insect repellent on yourselves and especially on your children, so that they do not get bitten by mosquitoes and inadvertently, contract dengue.

I would like to ask the Minister, does NEA face any difficulties in accessing individual homes, whether in private estates or HDB estates? What measures are being taken to deal with this issue?

Generally speaking, it has not been difficult to access homes. When our NEA inspectors knock on doors, they would open the doors. But sometimes, there is nobody at home, or sometimes, it could be an elderly at home. So, we try very hard to work with the neighbours to find out how we can get access. Particularly for areas which are dengue clusters, we do not wait long. We will try to gain entry and NEA has the powers to do so.

I want to commend the very diligent NEA ground staff and, of course, the volunteers who walk the blocks and flats with them to educate and to warn residents about dengue prevention. As the Minister mentioned, most of the mosquito-breeding habitats are in-house. We found that, on the ground, many of the NEA staff and the volunteers are very helpless when residents refuse to let them gain entry, sometimes, out of non-cooperation, but a lot is also out of fear of the fine, the stick; thinking that when they open the doors, if they would be punished.

I was wondering if NEA could consider to, first, issue a severe warning, get entrance to the flat, check the premises and then, install the fine only from the second time that they visit. There is a lot of worry, fear and anxiety about someone coming to your house, inspecting your premises and then, punishing you straightaway, when you are not yet educated or aware.

I am quite sure if you go through some Hansard reports, this question had been asked before – can we first give a warning, then issue the fine later, be kind? I think if dengue does not cause death, we probably could do that. But dengue is known to cause death and these could be our loved ones. I think everyone has to be responsible and accountable to take care of their homes, to make sure they do not breed mosquitoes. When NEA officers and dengue volunteers go in to check their homes, they are trying to help, and also point out where possible breeding habitats could be found; and then, if found, they fine them. That sends a strong signal to everybody to take this seriously. We never know which breeding habitat will produce the mosquito that may kill somebody we love.