By NewsDesk @bactiman63
In 2013, Singapore reported the largest dengue fever outbreak in recent history recording some 22,318 cases and eight deaths.
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 and eventually peaked in July 2020 with 1792 cases in a week.
Why the dengue fever surge in 2020?
The National Environment Agency (NEA) listed a number of factors:
- 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, signaling 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 harbor 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.