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NEA Urges Continued Vigilance As Aedes Aegypti Mosquito Population Remains High And Dengue Cases Rise At Start Of 2022

25 Jan 2022

Risk drivers for dengue in 2022 include the continued high Aedes aegypti mosquito population and recent increase in dengue cases, amid higher circulation of the less common Dengue virus serotype 3 (DENV-3) in large dengue clusters across the island.

Singapore, 25 January 2022 – Dengue cases have increased in the past five weeks, with 183 cases reported last week. A contributing factor and key concern is the high Aedes aegypti mosquito population detected in the community, which has increased by about 17 per cent in December 2021 compared to in August 2021. More cases of the less common Dengue virus serotype 3 (DENV-3) have also been detected in large dengue clusters across the island. If left unchecked, the current high Aedes aegypti mosquito population – together with circulation of the previously uncommon DENV-3, sizeable proportion of people still staying in and working from home, and current increasing number of dengue cases – may lead to a surge in dengue cases in the coming months. NEA therefore urges members of the public and other stakeholders to stay vigilant and not let their guard down, as dengue remains a serious public health threat.

Review of Dengue Situation in 2021 and Outlook for 2022

2          The total number of dengue cases reported in 2021 was 5,258. This came after a two-year outbreak in 2020 (35, 315 cases) and 2019 (15, 998 cases), which created cross-protective immunity [1] in the community. However, cross-protective immunity against other serotypes is short-lived and likely to be waning, leading to weekly dengue cases rising since end-2021. Contributing to this has been the upward trend in Aedes aegypti mosquito population in the community, which remains high in some areas of Singapore – including Ang Mo Kio Avenue 3, Hougang Avenue 7, Marsiling Drive/ Marsiling Road, and Champions Way/ Woodlands Avenue 1.

3          As of 24 January 2022, there are 24 active dengue clusters, with four large clusters at Cleantech Loop, Jalan Bangau, Denham Close/ Dunearn Road/ Hua Guan Avenue, and Dunearn Road. DENV-3 has been detected in two of these four large dengue clusters. Prior to 2020, DENV-3 had not been the dominant virus serotype during any major dengue outbreaks in Singapore over the past three decades. Thus population immunity against DENV-3 is low, and more people are susceptible to infection with this serotype.

4          Many people are still currently staying in and working from home, which could translate to more biting opportunities for the day-biting Aedes aegypti mosquito, and thus potentially higher risk of dengue transmission. With the presence of key drivers for dengue transmission – including low population immunity to DENV-3, increasing Aedes aegypti mosquito population, and continued work from home arrangements – we are expecting dengue case numbers in 2022 to exceed that in 2021. Concerted community action and sustained vector control efforts are urgently required, to prevent escalation of dengue case numbers to outbreak levels.

5          In 2021, NEA conducted about 631,000 inspections for mosquito breeding islandwide, and uncovered about 18,500 mosquito breeding habitats. During the same period, 8,700 enforcement actions [2] were taken against owners of premises for mosquito breeding. About 480 summonses and 43 Stop Work Orders were issued to construction sites, and 54 contractors were charged in court for repeat offences. Since implementation of heavier penalties against homes on 15 July 2020, NEA has detected multiple mosquito breeding in about 770 residential premises inspected, and repeated mosquito breeding in about 1,100 residential premises inspected.

Figure 1 - Nos of dengue

Figure 1. Number of dengue cases from 2018 to 2022 (as of E-week3)

Advisory for Lunar New Year Period

6           Aedes mosquitoes can breed in clean stagnant water found in homes and other premises. As the Lunar New Year festive season approaches, homes and other premises are decorated with more ornamental plants. In anticipation of this, NEA has completed inspections of all plant nurseries. This year, NEA has distributed to plant nurseries a festive dengue prevention package, which includes red packets, plant pot stickers and posters with dengue prevention messages, to remind both plant sellers and buyers to maintain vigilance and prevent mosquito breeding (refer to Annex for visuals of the package items). To reach out to more plant owners, NEA is partnering plant nurseries in a series of contests hosted on the Clean & Green Singapore Instagram account (@cleanandgreensg). All stakeholders are urged to prevent mosquito breeding and keep the mosquito population low, by regularly practising the following Mozzie Wipeout ‘B-L-O-C-K’ steps:

B-L-O-C-K’ steps

Break up hardened soil
Lift and empty flowerpot plates
Overturn pails and wipe their rims
Change water in vases
Keep roof gutters clear and place BTI insecticide

7         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. Those decorating their homes and premises with ornamental plants are urged to take care of these plants and prevent them from becoming mosquito breeding habitats, by making sure that water does not accumulate in the flowerpot plates or on top of the hardened soil.

[1] Cross-protective immunity to Dengue virus serotypes is the protection against one serotype due to pre-existing immunity developed from past exposure to a different serotype. It is only partial and temporary, with research studies generally showing a timeframe of between a few months and a few years.  

[2] Enforcement figures provisional as of 11 Jan 2022

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Festive Dengue Prevention Package for Plant Nurseries

The Festive Dengue Prevention Package for plant nurseries includes:

1)    An instructional flyer to explain about the items in the package

2)    Red packets (2 designs) to be given out to the nurseries’ customers

3)    Plant pot stickers (2 designs) to be given out to the nurseries’ customers

4)    Festive poster to be displayed within the nurseries

5)    B-L-O-C-K Dengue in our Neighbourhoods poster (2 pages) to be displayed within the nurseries

1) Instructional Flyer

Instructional Flyer 1Instructional Flyer 2
 Front Back

2) Red Packets

Red Packets 1Red Packets 2Red Packets 3Red Packets 4
 Design 1 – Hoya (Front and Back) Design 2 – Pothos (Front and Back)

3) Plant Pot Stickers

Plant Pot Stickers 1Plant Pot Stickers 2
Design 1 – Hoya Design 2 – Pothos  

4) Festive Poster

Festive Poster
Key Visual - Homalomena

5) B-L-O-C-K Dengue in our Neighbourhoods Poster

B-L-O-C-K Dengue 1B-L-O-C-K Dengue 2
 Page 1 – English and Malay Page 2 – Chinese and Tamil