Increasing Aedes aegypti mosquito population detected across the island. Higher circulation of less common Dengue virus serotypes 3 and 4 (DENV-3 and DENV-4) is of concern, as more people are susceptible due to lower population immunity. People may have higher exposure to Aedes mosquito bites and dengue transmission, while staying in and working from home.  

Singapore, 1 June 2021 – Over 2,700 dengue cases have been reported since the start of this year, and there are currently 22 active dengue clusters. Recent weekly dengue cases have been lower than in the same period in 2020, when Singapore experienced a historic outbreak year. However, these figures are still higher than those reported in 2017 and 2018. As we have now entered the warmer months of the year, the increased risk of higher dengue transmission is a concern. NEA expects an increasing number of dengue cases due to the accelerated breeding cycle and maturation of the Aedes mosquito vectors, as well as the shorter incubation period of the Dengue virus.

2          Of significance is the increasing Aedes aegypti mosquito population across the island. The population increased by about 30 per cent in the month of April 2021 compared to January 2021, and remains high in some areas of Singapore. These areas include Clementi West Street 1, Hougang Avenue 10 / Hougang Avenue 6 / Hougang Avenue 8, Jurong East Avenue 1 / Jurong East Street 32, and Mei Chin Road / Mei Ling Street / Stirling Road.

3          Cases due to the less common Dengue virus serotypes 3 and 4 (DENV-3 and DENV-4) make up more than half the serotypes sampled since February 2021. DENV-3 has not been dominant since about three decades ago, and the incidence of DENV-4 has been consistently low. Thus the population immunity for DENV-3 and DENV-4 is low, and more people are susceptible to transmission of the virus. DENV-3 has been detected in the dengue cluster at Cashew Terrace / Hazel Park Terrace. DENV-4 has been detected in clusters at Hougang Central and Pasir Ris Street 21.

4          The COVID-19 Phase 2 (Heightened Alert) measures from 16 May to 13 June 2021 are seeing more people staying in and working from home, which could translate to more biting opportunities for the day-biting Aedes aegypti mosquito (the primary dengue vector), and thus potentially higher risk of dengue transmission. 

5          In August 2020, NEA and Saw Swee Hock School of Public Health, National University of Singapore (NUS), carried out an epidemiological study to examine the independent effect of the Circuit Breaker period on the number of reported dengue infections. The study found almost 50 per cent more infections during the Circuit Breaker period than there should have been, based on mathematical modelling. Most of the excess infections were among adults of working age (20 to 64 years old) – people who would normally have been in workplaces, some of which would have been air-conditioned, instead of their homes.

6          If left unchecked, the current high Aedes aegypti mosquito population, coupled with the circulation of previously uncommon Dengue virus serotypes and a sizeable proportion of people staying in and working from home, would add to the dengue risk this year. NEA therefore urges all members of the public to prevent mosquito breeding, by immediately practising the following Mozzie Wipeout steps at least once a week, to remove stagnant water:

Mozzie Wipeout ‘B-L-O-C-K’

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          All premises owners and operators should ensure that comprehensive vector control measures and good housekeeping are in place. NEA continues to conduct targeted inspections at areas with higher mosquito population, and has stepped-up operations at dengue clusters. All residents, especially those living in dengue cluster areas are encouraged to carry out the three protective actions against dengue:

Protective actions against dengue: ‘S-A-W’ 

Spray insecticide in dark corners around the house
Apply insect repellent regularly
Wear long-sleeve tops and long pants

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