SG’s cramped migrant worker dorms prone to COVID-19 outbreaks

While the strict and rapid implementation of border restrictions, contact tracing, case isolation, social-distancing, and quarantine protocols can effectively suppress COVID-19 transmission, densely populated environments, as in the case of migrant worker dormitories in Singapore, remain at risk of outbreaks, according to a recent study.

“Prioritization of these settings in vaccination strategies should minimize the risk of future resurgences and potential spillover of transmission to the wider community,” the researchers said.

Two prospective serological cohort studies were conducted: one in a SARS-CoV-2-affected migrant worker dormitory including 478 residents (mean age 35 years, 100 percent men) and another in 937 community-dwelling adult Singapore residents (mean age 52 years, 51.2 percent women). Incidence rates of COVID-19, the main outcome measure, were compared between cohorts.

A total of 117 migrant workers tested positive for SARS-CoV-2-neutralizing antibodies at baseline, corresponding to a prevalence rate of 24.5 percent. Positivity rose to 37.2 percent after 2 weeks and 51.3 percent after 6 weeks of follow-up. [Int J Infect Dis 2022;155:72-78]

Accounting for test-related factors resulted in a cumulative seroprevalence rate of 30.4 percent at baseline, climbing to 46.5 percent and 63.8 percent after 2 and 6 weeks, respectively. Notably, workers who were initially seronegative saw a 22.9-percent risk of conversion after 2 weeks, which worsened to 54.3 percent after 6 weeks.

Moreover, the researchers reported significant clustering of cases by room, an effect that was strongest at baseline. As seropositivity rose during the second and sixth weeks, such clustering became less evident.

Most migrant workers were asymptomatic, with only five (4.3 percent) of those seropositive at baseline experiencing COVID-19 symptoms; only six seroconverters (3.8 percent) showed symptoms during follow-up.

The community cohort, on the other hand, showed a 0.21-percent seropositivity rate as compared to prepandemic levels. Accounting for test-related factors yielded a cumulative seropositivity of 0.16 percent. A total of 2,272 community cases were reported in Singapore up until the end of 2020 with a cumulative incidence rate of 0.042.

“Our results demonstrated the continuing effectiveness of nationally implemented, wide-ranging control measures for minimizing community transmission of SARS-CoV-2, while emphasizing the challenges to mitigating risk in densely populated settings,” the researchers said. “Our study also documented evidence of high rates of asymptomatic infection in migrant workers.”

“Although the routes of transmission within the migrant worker dormitory were not specifically investigated, the strong clustering of infection within rooms highlights the role of crowding in transmission and emphasizes the need to reduce density in dormitory settings in order to reduce vulnerability to outbreaks,” they added. Prioritizing these populations for vaccination should also be considered.