Dengue: A Tale Of Two Lockdowns

COVID-19 lockdown measures decreased the rate of dengue among migrant workers but raised it in Singapore’s general population.

AsianScientist (May 14, 2021) – While COVID-19 lockdown measures led to a marked increase in cases of dengue among Singaporeans, they also led to a fall in dengue cases in the country’s migrant worker population. These were the surprising findings of a pair of studies published in the Journal of Infectious Diseases and the Journal of Travel Medicine.

Having claimed over three million lives around the globe, COVID-19 is rightly at the top of the news cycle. However, other less headline-grabbing killers like heart disease and cancer continue to exert their toll—pandemic or not. In Singapore, where mosquito-borne dengue is endemic, the country experienced its largest dengue outbreak to date in 2020, with over 35,000 people infected and at least 29 deaths.

“This outbreak coincided with the pandemic measures, and given the unprecedented changes in our behavior and mobility during lockdown periods, it seemed natural that one unprecedented event might have influenced the other,” said Alex Cook, an associate professor at the Saw Swee Hock School of Public Health, National University of Singapore (NUS).

To investigate the impact of Singapore’s ‘circuit breaker’ social distancing policy on dengue infections, Cook and his team compared dengue case counts before and after the implementation of lockdown measures in 2020. Focusing on those aged between five and 65, the researchers found that there was a 37 percent increase in case counts compared to baseline levels.

“We know that in regular times, many dengue cases are not linked to a domestic cluster. This could be due to under-diagnosis of infections in an actual domestic cluster, or because of infections happening far from home—at work or hawker centers for instance,” Cook said. “It was a bit of a surprise then that infection rates in the general community increased during the period of lockdown.”

The situation was reversed, however, for migrant workers. Controlling for potential confounders such as seasonality and population size, Cook and his team found that there was a reduction of about 432 cases of dengue in migrant workers during the lockdown period from April 7 to June 1.

“Our finding that dengue infections went down for foreign workers living in dormitories is, in a way, expected,” Cook said, noting that having common toilets make it easier for dorm operators to prevent mosquito breeding.

“Working outdoors at a worksite exposes workers to a higher risk of being bitten than working in an air-conditioned office, so by removing that risk for the period of lockdown, the infection rate among foreign workers was expected to fall.”

While the studies do not explain why the shutting down of workplaces led to different dengue infection rates for migrant workers and the general population, they highlight the need to remain on the lookout for other diseases even as the levels of COVID-19 infections rise and fall.

“As with COVID-19, in the long run, the best bet for reducing dengue transmission lies in an effective, widely used vaccine. However, until we have that, our studies show the importance of families implementing the ‘mozzie wipeout’ in and around their homes,” Cook concluded.

The articles can be found at:
Lim et al. (2021) Increased dengue transmissions in Singapore attributable to SARS-CoV-2 social distancing measures.
Lim et al. (2021) Decreased dengue transmission in migrant worker populations in Singapore attributable to SARS-CoV-2 quarantine measures.


Copyright: Asian Scientist Magazine; Illustration: Alexandra Valino/Asian Scientist.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Charlene Kok is pursuing medicine at the University of Glasgow, UK. She has a keen interest in scientific discovery and is passionate in applying them to aid others.

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