Coronavirus outbreaks most common in homes, transport: Study

Outbreaks at home were the most common type of coronavirus transmission, followed by transportation, researchers in China found.

The research team found that nearly 80% of 318 outbreaks with three or more cases happened in the household. The outbreaks, which included 1,245 confirmed cases in 120 cities, were divided into six categories of venue: home, transportation, food, entertainment, shopping and miscellaneous.

Among the identified outbreaks, almost 54% involved three cases, about 26% involved four cases and less than 2% involved 10 or more cases. Most home outbreaks involved three to five cases, according to the study.

“It emphasizes the importance of indoor space as a place where transmission will occur,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University. “And it looked like the contact was very close. They didn’t have any real evidence of airborne transmission of clusters of people who were widely dispersed, which is also reassuring.”

Transportation followed home outbreaks at 34%. However, the study’s authors noted many outbreaks involved more than one type of venue. If double or triple counting the venues, 318 outbreaks touched 416 venues. The researchers pinpointed only one outbreak in an outdoor environment, which involved two cases.

Similar to other respiratory viruses, the coronavirus appears to transmit more indoors than outdoors, said Dr. Amesh Adalja, senior scholar for the Johns Hopkins Center for Health Security.

“Outdoors, a person is more likely to be able to socially distance than indoors and there are less common touch surfaces. As social distancing guidance is modified, outdoor activities may be relatively safer than indoor activities,” Dr. Adalja said. “It is important to remember, also, that the physical isolation that we’re doing currently is with individuals who are presumably not infected so that would not really have an impact on transmission.”

Out of the 318 outbreaks, 129 involved only family members, 133 involved relatives, 29 involved socially connected individuals, 24 involved socially non-connected, and only three involved multiple relationships.

Eighty-three of the identified outbreaks had multiple possible venues, which means the exact venue of infection couldn’t be identified or that multiple venues were involved in the infection.

Fourteen outbreaks occurred at a restaurant or other food venue. Seven were pinpointed to an entertainment venue, and seven to a shopping venue. An additional 26 outbreaks occurred at a miscellaneous venue such as a hospital, hotel room or thermal power plant.

“The lesson we need to learn is to focus our public health attention strongly on congregate indoor settings such as homes, apartments, shelters, nursing homes. That is where transmission is most likely to occur,” said Lawrence Gostin, a global health law professor at Georgetown University.