By Philip R. Fischer, MD, DTM&H

Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN; Department of Pediatrics, Sheikh Shakhbout Medical City, Abu Dhabi, United Arab Emirates

SYNOPSIS: In areas where daytime-biting Aedes mosquitoes transmit dengue virus, lockdowns and stay-at-home orders can either increase or decrease the incidence of dengue fever — depending on whether there are more mosquitoes in the home or work environment.

SOURCES: Lim JT, Chew LZX, Choo ELW, et al. Increased dengue transmissions in Singapore attributable to SARS-CoV-2 social distancing measures. J Infect Dis 2021;223:399-402.

Lim JT, Dickens BL, Ong J, et al. Decreased dengue transmission in migrant worker populations in Singapore attributable to SARS-CoV-2 quarantine measures. J Travel Med 2021;28:taaa228. doi 10.1093/jtm/taaa228

Aedes mosquitoes are responsible for transmitting dengue virus and causing more than 100 million cases of dengue fever each year. These mosquitoes bite during daytime hours. Dengue fever is common in Singapore.

Singapore adopted strict stay-at-home programs to supplement personal social distancing to reduce the spread of SARS-CoV-2. Approximately 95% of workplaces were closed, as were schools and recreational facilities. Lim and colleagues wondered if staying at home altered the risk of getting dengue fever.

In the Journal of Infectious Diseases, Lim and colleagues reported on the use of weekly and seasonal dengue incidence rates prior to and during the COVID-19-induced lockdowns as relevant to individuals ages 5 to 65 years, thus including those who normally would be at school or in offices during the daytime hours. There was a 37% increase in cases of dengue fever during the weeks of the pandemic-induced lockdown. In Singapore, dengue transmission seems to be greater in windowed homes than in air-conditioned offices and schools, so it was not surprising that there would be more dengue infection when people spent more days in areas to which mosquitoes had free access.

In the Journal of Travel Medicine, Lim and colleagues reported on dengue fever transmission in migrant worker populations in Singapore. The migrant workers usually live in high-occupancy dormitories with controlled air flow and work in outdoor settings, such as in jobs related to construction. Migrant workers living in dormitories had nearly 100-fold higher incidences of COVID-19 than did the population living in family residences. Lim and colleagues extended their work on dengue transmission in the era of COVID and sought to evaluate the risk of dengue in migrant workers. Indeed, migrant workers had a 69% reduction in the incidence of dengue during the weeks they stayed at home. Thus, while staying with groups in dormitories facilitated transmission of SARS-CoV-2, it kept migrant workers indoors in environments less conducive to Aedes mosquitoes and reduced transmission of dengue virus.

COMMENTARY

In March 2021, Infectious Disease Alert reported on unexpected benefits of social distancing for children. Staying away from groups of people was associated with reductions in acute illness visits, emergency department visits, and overall hospitalizations for medical problems. Now, these new data from Singapore show how staying at home can alter the risk of mosquito-borne illness.

Lim and colleagues evaluated the risk of dengue fever for school-attending and office-working groups, and they similarly evaluated the risk of dengue for migrant workers. Although there had been previous concern about the risks of dormitory living on disease transmission (and there was a corresponding increased risk of getting COVID-19), it turns out that dorm living is safer, in terms of dengue acquisition, than either working outdoors or living in single-family residences.

Wherever in the world we live, COVID-19 and its necessary social distancing have altered our interactions with other people. However, Lim’s papers remind us to remain vigilant to avoid spending time socially approximated to mosquitoes at times when they are seeking blood meals. In areas where Aedes transmit viruses such as dengue, Zika, chikungunya, and yellow fever, daytime mosquito avoidance measures become more important when social distancing leaves people in closer proximity to fresh circulating air.