SINGAPORE: 2020 will be remembered primarily for the COVID-19 pandemic, which killed more than a million people and infected countless more worldwide.
But in the shadow of the pandemic, another plague lurks, a long-standing public health threat in tropical and subtropical regions of the world.
We’re referring, of course, to dengue, which infected over 30,000 people in Singapore this year, with more than 1,000 cases per week for most of June through August.
This is an all-time high, beating the highest previous record of 22,170 dengue cases in 2013 and the highest weekly high of 891 cases in 2014.
Earlier this year we saw signals of an impending major dengue outbreak, both in the high number of dengue cases and in the increase in the incidence of the unusual DENV-3 serotype.
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The National Dengue Prevention Campaign was therefore launched in March by the National Environment Agency (NEA) before the usual start in May, which coincides with the start of the “dengue season”, to mobilize the nation to conscientiously keep the budget get rid of standing water and deprive the Aedes mosquitoes of breeding habitats.
Despite preventive measures and extensive public communications, the infection numbers reported weekly soon surpassed previous outbreak trends, suggesting that other factors may have exacerbated the surge.
Use for dengue prevention in a city center. (Photo: NEA)
Dengue transmission increases when there is more contact between Aedes mosquitoes and humans, either because people are more exposed to the bites of Aedes mosquitoes or because the mosquito population increases. Could these have been a by-product of our response to the COVID-19 pandemic?
CIRCUIT BREAKER CONTRIBUTE TO THE DENGUE OUTBREAK, HOW MORE STAYS AT HOME
The answer is yes. As more and more people spend more days in naturally ventilated homes, the likelihood of mosquitoes getting the infection from dengue-infected people and passing it on if they bite healthy people had increased.
This is due to the biology of the Aedes aegypti mosquito, the main vector of dengue fever. The mosquito is known to bite during the day, peak at dusk rather than at night, and live in human habitats.
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In August, NEA and the Saw Swee Hock School of Public Health conducted an epidemiological study to examine the independent impact of the breaker period on the number of reported dengue infections.
We detected nearly 50 percent more infections during the breaker period than our modeling should have been. This also applies after taking into account the typical increase in dengue cases in the middle of the year and the high level of infection in the first two months of the year.
Most of the excessive infections affected adults of working age (20 to 64 years old) – people who had spent much more of their day at home and normally would have been to offices, factories, and stores.
Use for dengue prevention in a city center. (Photo: NEA)
The younger population (ages 5 to 19) had only 12 percent more cases, possibly because schools were closed for a shorter period than the full duration of the breaker.
In addition, unlike working adults, school children would have spent much of Aedes’ peak bite time at home at dusk, even before the circuit breaker was turned on.
Mosquito exposure is less likely to change for elders and preschoolers as they would spend more time at home prior to the breaker period and therefore constitute a suitable reference population for analysis.
It is clear that the increasing proximity of people and mosquitoes has led to a rapid increase in the number of new dengue infections.
CIRCUIT BREAKER MEASURES INCREASED MOSQUITO GROWTH
Despite repeated public notices of dengue risk, Aedes aegypti mosquito breeding in Singapore continued to increase during the breaker period.
The average percentage of inspected construction sites found in mosquito breeding from January to March was six percent. That number tripled to 18 percent from April to June, though it has since fallen to about 10 percent in August.
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This is likely because the cessation of construction activity since the start of the breaker period on April 7, 2020 had left the construction sites largely unattended and exposed to tropical weather with regular rainfall.
Additionally, the lockdown of many of our essential staff to curb COVID-19 transmission in dormitories has reduced the frequency of cleaning public spaces.
NEA officer checks for mosquito breeding in public areas. (Photo: NEA)
The number of mosquitos in private households also remained high during the breaker, which contradicted some expectations that those who spend more time at home would be able to remove standing water.
NEA reported a five-fold increase in the incidence of Aedes mosquito larvae detected in residential areas and shared corridors in residential areas during the two-month breaker period compared to the two months prior.
Could the unexpected increase in home mosquito breeding be due to the challenges residents face when working from home, the increased household burden with more people at home, or the fact that housewives are more focused on preparing home-cooked meals and the Have to watch out for monitoring children who would otherwise be in school?
Although dengue cases have decreased over a seven-week period in the past few weeks, it remains high at 595 in the past week. With a significant portion of our workforce continuing to work from home and at a higher risk of developing dengue fever, the decline in dengue cases could be long and slow.
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Dengue has killed more than 20 people so far this year, and there may be more if we don’t work together to take immediate and decisive action.
INDIVIDUAL ANSWERS REQUIRED TO PROTECT FAMILIES
Everyone has a role to play in the fight against dengue because each of us can become a hub for dengue transmission and the Aedes aegypti mosquito breeds in our homes.
One way to fight dengue is to keep yourself from getting bitten. This is especially important for people with dengue fever as they are a potential source of infection for others.
If you live in a dengue-risk area, you and your family should wear long pants, long-sleeved clothing, and use mosquito repellants to protect yourself from mosquito bites, especially during the peak Aedes aegypti mosquito bite periods in the early morning and late morning afternoon.
A worker sprays insect repellant as a preventative measure against the spread of dengue fever in a neighborhood garden in Singapore on Aug. 25, 2020. (AFP / Roslan RAHMAN)
You can protect your home by spraying insecticides in the mosquito’s hiding spots. These spots can be under sofas, tables or shelves, behind curtains or in dark parts of the kitchen.
A light, targeted spray of insecticide in these areas – not vaguely in the air – can help kill mosquitoes around the home. NEA has a video that shows how to do this.
Another longer-term solution is to put mosquito screens on your windows.
To remember to check for and remove stagnant water, at a convenient time (such as after dinner), you should put a reminder on your phone with a two-day repetition.
REQUIRED SOCIAL RESPONSES: PROTECT COMMUNITIES
During a major outbreak like this, we must take a common approach to preventing dengue fever in our neighborhood. Pro-social neighborhood encouragement can help overcome one of the main barriers to dengue prevention, which is the indolence resulting from the habit of not taking action.
There are inspiring initiatives in the church. For example, members of an east coast housing council, concerned about the increase in dengue cases infecting many people in their neighborhood, made proactive efforts to vet the residents of their property and make sure they knew how they were and theirs Protect families can get infected.
File photo of a fog operation in Geylang. (Photo: Try Sutrisno Foo)
What makes the COVID-19 pandemic so different from the pandemic past is that we have launched an unprecedented response to it – closing schools, borders, mosques, churches and temples, shops, cinemas, workplaces, wearing masks, social distancing , Travel restriction and contact tracking.
As a society, we have done more recently to stop the spread of COVID-19 than we have done with any other disease.
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The response, both how we have accepted it and how the pandemic has been kept in check so far, shows what can be achieved if we work together to contain a public health threat.
Associate Professor Alex Cook is the Vice Dean of Research at the Saw Swee Hock School of Public Health at the National University of Singapore.
Associate Professor Ng Lee Ching is the Group Director of the National Environment Agency’s Environmental Health Institute. She provided expert advice to the World Health Organization.