Reasons for Recent Surge in Dengue Cases

Mr Liang Eng Hwa asked the Minister for Sustainability and the Environment (a) what are the reasons for the recent surge in dengue cases; and (b) what are the short- and medium- term measures to reduce overall dengue cases.

Mr Yip Hon Weng asked the Minister for Sustainability and the Environment whether the reduction in grass-cutting and tree-pruning activities due to the COVID-19 pandemic has caused the rise in dengue cases in housing estates.

Mr Leon Perera asked the Minister for Sustainability and the Environment (a) what is the number of dengue cases in the past six months; (b) what has been the progress of anti-dengue efforts; and (c) what has been the progress of Project Wolbachia.

As of 29 August 2020, there were 27,281 dengue cases reported this year. Of these, about 24,000 cases were reported in the past six months, from March to August 2020.

A confluence of factors contributed to the surge in dengue cases. First, the less common DENV-3 was dominant in the first four months of this year and remains high. As this serotype had not been prevalent in the last three decades, our population has low herd immunity and this facilitates rapid disease transmission.

Second, NEA's Gravitrap surveillance system detected a 30 per cent increase in the Aedes aegypti mosquito population from May to June 2020, compared to the period February to March 2020. Coupled with the warmer and wetter weather as we entered the traditional peak dengue season from May onwards, the momentum of the high dengue case load sustained the high number of cases seen in June and till today.

Third, the spike in dengue cases coincided with the two-month Circuit Breaker (CB) period. The weekly number of dengue cases started to rise sharply from May 2020. With more people staying at home, there were more human targets for the female Aedes aegypti mosquitoes.

Finally, the scaling back of services for cleaning and facilities maintenance during the CB period, including stoppage of work at construction sites, could have also compounded the dengue situation. In some cases, overgrown grass may have concealed discarded receptables which could become potential breeding sites. However, this issue is being addressed as cleaning and associated services have resumed.

NEA has scaled up efforts on all fronts since the end of the CB, working with stakeholders.

First, NEA has an intensive inspection regime. Majority of breeding was found in homes. In May and June alone, it carried out 107,000 inspections of homes, and detected and destroyed about 2,600 mosquito breeding habitats. Another 2,700 mosquito breeding habitats were destroyed during inspections of condominium grounds, construction sites, common areas and other premises.

Second, to deter mosquito breeding, NEA has tightened the enforcement regime for Town Council managed areas, construction sites, and residential premises since 15 July 2020. For example, NEA has increased composition fine amounts in instances of repeated breeding offences, or multiple breeding habitats detected during a single inspection.

Third, on 24 July, NEA launched an intensive vector control exercise with Town Councils, Grassroots Advisers and leaders, and community volunteers. Town councils were called upon to step up housekeeping efforts to keep common areas litter-free, remove stagnant water, maintain drains, as well as work with NEA to conduct coordinated chemical treatment such as fogging, misting and applying larvicide in common areas. Most Town Councils have completed desilting and flushing of drains in the larger dengue clusters, and have moved on to also tackle other areas with high mosquito population. NEA has been auditing Town Councils to ensure that housekeeping efforts are satisfactory.

Fourth, NEA has stepped up collaboration with stakeholders on dengue prevention. For example, NEA is working with community partners, such as Grassroots Advisers and Leaders, as well as community volunteers, to reach out to residents with messages on how to prevent mosquito breeding and protect themselves against mosquito bites. Together with the People's Association and Ministry of Health, 700,000 bottles of repellent were distributed to residents in active dengue clusters and another 300,000 bottles were distributed by Polyclinics and General Practitioners to suspected dengue patients. Recently, NEA partnered the Ministry of Education to provide 46,000 bottles of repellent to students in 37 schools located in large dengue clusters, to protect the students and educate them and their families on how to protect themselves against dengue.

Fifth, NEA has launched successive public communications campaigns on both mainstream and online media. NEA has expanded the number of dengue alert banners displayed at neighbourhood precincts of dengue cluster areas, and brought the message closer to residents with dengue alert posters at the individual HDB blocks. Residents living in cluster areas are also receiving SMS reminders to check their homes for stagnant water and do the Mozzie Wipeout.

These efforts have borne some initial results. We have seen about a 20% decline in dengue cases in recent weeks. About 84 per cent of the 2,253 clusters reported in 2020 have closed as of 31 August 2020. This includes the large dengue clusters at Bartley Road, Tampines Avenue 7, Cassia Crescent, Dakota Crescent, Leicester Road, Potong Pasir Avenue 1 and Braddell Road. However, the overall number still remains high and we cannot let our guard down.

While NEA puts in concerted efforts on dengue control, we are continuing with the Project Wolbachia trials and expanding to new areas. The phased field studies at Yishun and Tampines have been promising, with the Aedes aegypti population being suppressed by 90 per cent. Preliminary analysis has shown that 65 to 80 per cent fewer dengue cases are observed at the study sites, compared to areas without releases. NEA has progressed to Phase 5 of Project Wolbachia in July 2020, which will involve releases for the whole towns of Tampines and Yishun, covering 1,455 blocks or about 15 per cent of all HDB blocks in Singapore. In addition, since May 2020, NEA has been testing a more targeted release strategy in areas with higher risk of dengue in Choa Chu Kang and Bukit Batok towns, to pre-emptively suppress the high Aedes aegypti population in these areas. These releases cover an additional 207 blocks.

Despite the success of the trials, Wolbachia is not a silver bullet; nor is it ready for immediate deployment. Constant efforts are still required to find innovations and engineering solutions to automate and sustain the mosquito production and release processes, before Wolbachia can be implemented on a larger scale. More importantly, Wolbachia technology cannot replace the community's efforts to ensure good housekeeping, which will always be needed to keep our homes and estates free from mosquitoes and dengue.

The current conditions are challenging. We are still in the peak dengue season and an all-out national effort is necessary to win the battle against dengue. NEA and partner agencies are committed to do our best to sustain the efforts. I urge all residents, especially those residing in dengue cluster areas, to do their part and take the three protective actions against dengue – spray insecticide in dark corners around the house, apply insect repellent regularly, and wear long sleeves and long pants. Residents should also continue to do the Mozzie Wipeout and ensure that their homes and surroundings are free of stagnant water.