Effectiveness of Strict Social Distancing in Controlling Contagion: Predictive Modeling Insights

Johns Hopkins University Bloomberg School of Public Health

Using public transportation, visiting a place of worship, or traveling from home is associated with a significantly higher likelihood of testing positive with the SARS-CoV-2 coronavirus, while practicing strict social distancing is associated with a markedly lower likelihood , suggests a study by researchers at the Johns Hopkins Bloomberg School of Public Health.

For their analysis, the researchers surveyed a random sample of more than 1,000 people in the state of Maryland in late June, asking about their social distancing practices, use of public transportation, history of SARS-CoV-2 infection, and others. COVID-19- relevant behaviors.

They found, for example, that those who reported frequent use of public transportation were more than four times more likely to report a history of positive tests for SARS-CoV-2 infection, while those who reported practicing strict social distancing when outdoors were only a tenth as likely. to report ever having been positive for SARS-CoV-2.

The study is believed to be among the first large-scale assessments of COVID-19-relevant behaviors that rely on individual-level survey data, as opposed to aggregated data from sources such as cell phone apps.

The results were published online September 2 in Clinical Infectious Diseases .

"Our findings support the idea that if you’re going out, you should practice social distancing as much as possible because it appears to be strongly associated with a lower chance of getting infected ," says study lead author Sunil Solomon, MBBS, PhD, MPH, associate professor in the Department of Epidemiology at the Bloomberg School and associate professor of medicine at Johns Hopkins School of Medicine. "Studies like this are also relatively easy to do, so we believe they have the potential to be useful tools for identifying places or population subgroups with greater vulnerability."

The new coronavirus SARS-CoV-2 has infected almost 27 million people worldwide, of whom about 900,000 have died, according to the World Health Organization. In the absence of a vaccine, public health authorities have emphasized practices such as staying home, wearing masks and maintaining social distancing in public. However, there has been no good way to monitor whether, and among which groups, such practices are being followed.

Solomon and his colleagues, including first author Steven Clipman, a PhD candidate in the Bloomberg School’s Department of International Health, quickly accessed willing survey participants through a company that maintains a large pool of potential participants nationwide. as a commercial service for market research.

All 1,030 people included in the study lived in Maryland, which has recorded more than 113,000 confirmed cases of SARS-CoV-2 and nearly 3,700 confirmed deaths, according to the Maryland Department of Health.

The researchers asked survey participants questions about recent travel outside the home, their mask use, social distancing and related practices, and any confirmed SARS-CoV-2 infections either recently or not at all.

The results indicated that 55 (5.3 percent) of the 1,030 participants had tested positive for SARS-CoV-2 infection at some point, while 18 (1.7 percent) reported testing positive in the two weeks before. of being surveyed.

The researchers found that when considering all the variables they could evaluate, spending more time in public places was strongly associated with having a history of SARS-CoV-2 infection.

For example, a history of infection was approximately 4.3 times more common among participants who reported that they had used public transportation more than three times in the previous two weeks, compared to participants who said they had never used public transportation. in the period of two weeks.

A history of infection was also 16 times more common among those who reported visiting a place of worship three or more times in the previous two weeks, compared to those who reported not visiting any place of worship during the period. The survey did not distinguish between visiting a place of worship for a religious service or other purposes, such as a meeting, summer camp, or a meal.

In contrast, those who reported practicing social distancing outdoors "always" were only 10 percent likely to have a history of SARS-CoV-2, compared to those who reported "never" practicing social distancing.

A relatively simple initial analysis linked many other variables to history of SARS-CoV-2 infection, including being black or Hispanic. But a more sophisticated "multivariate" analysis suggested that many of these apparent links were largely due to differences in movement and social distancing.

"When we adjusted for other variables such as social distancing practices, many of those simple associations disappeared, providing evidence that social distancing is an effective measure to reduce SARS-CoV-2 transmission," says Clipman.

The data indicated greater adoption of social distancing practices among some groups who are especially vulnerable to severe COVID-19 illness, suggesting they were relatively aware of their vulnerability. For example, 81 percent of participants ages 65 and older reported always practicing social distancing in outdoor activities, while only 58 percent of 18- to 24-year-olds did.

The results are consistent with the general public health message that wearing masks, social distancing, and limiting travel whenever possible reduce the transmission of SARS-CoV-2.

However, the researchers suggest that studies like these, which employ similarly rapid surveys of specific groups, could also become useful tools for predicting where and among which groups infectious diseases will spread most rapidly.

"We did this study in Maryland in June and it showed, among other things, that younger people in the state were less likely to reduce their risk of infection with social distancing, and a month later a large proportion of SARS infections- CoV-2 detected in Maryland was among younger people," says Solomon. "Therefore, it points to the possibility of using these rapid and inexpensive surveys to predict where outbreaks will occur based on behaviors and then mobilize public health resources accordingly."

Solomon and his team are now conducting similar surveys in other states and are studying the surveys’ potential as predictive epidemiological tools.