New research from Japan suggests that many coronavirus clusters outside of hospitals may have been started by people who are younger than 40 or don’t feel sick.
The findings offer insight into who might be driving coronavirus transmission -- and they underscore the importance of certain measures, such as face coverings, to slow the spread of Covid-19.
Researchers behind the study looked at more than 3,000 coronavirus cases in Japan. They identified 61 clusters linked to places such as health care facilities, restaurants, bars, workplaces and music events. A cluster was defined as five or more cases where people were exposed at a common venue – not including transmission within a household.
The researchers identified 22 patients who likely started clusters outside of hospitals; half of them were between 20 and 39 years old. That is “younger than the age distribution of all COVID-19 cases in Japan,” according to the study.
“We do not know whether social, biological, or both factors play a role in the difference in transmission patterns between the younger and older persons,” the researchers wrote.
“We also noted probable primary COVID-19 case-patients appear to transmit the virus and generate clusters even in the absence of apparent respiratory symptoms, such as cough.”
The research was published last week as an “Early Release” in Emerging Infectious Diseases, a journal from the US Centers for Disease Control and Prevention. That means it could see changes before being published.
Overall, the study found 18 clusters linked to health care facilities and ten linked to other care facilities such as nursing homes and day care centers.
Ten additional clusters were from restaurants or bars, eight were from workplaces, and seven were from music-related events such as live concerts, chorus group rehearsals and karaoke parties.
“The largest non–healthcare-related cluster we observed was among >30 persons who attended a live music concert, including performers, audience members, and event staff,” the researchers wrote. Five other clusters were linked to gyms, two to “ceremonial functions” and one to an airplane.
“We noted many COVID-19 clusters were associated with heavy breathing in close proximity, such as singing at karaoke parties, cheering at clubs, having conversations in bars, and exercising in gymnasiums,” the researchers wrote.