Researchers say similar studies could be used to predict local trends in infectious outbreaks
Johns Hopkins University 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, SARS-CoV-2 infection history, and other COVID-19-relevant behaviors.
They found, for example, that
those reporting frequent public transport use were more than four times as
likely to report a history of testing positive for SARS-CoV-2 infection, while
those who reported practicing strict outdoor social distancing were just a
tenth as likely to report ever being SARS-CoV-2 positive.
The
study is believed to be among the first large-scale evaluations of
COVID-19-relevant behaviors that is based on individual-level survey data, as
opposed to aggregated data from sources such as cellphone apps.
The results were published online on September 2 in Clinical Infectious Diseases.
"Our
findings support the idea that if you're going out, you should practice social
distancing to the extent possible because it does seem strongly associated with
a lower chance of getting infected," says study senior author Sunil
Solomon, MBBS, PhD, MPH, an associate professor in the Bloomberg School's
Department of Epidemiology and an associate professor of medicine at Johns
Hopkins School Medicine. "Studies like this are also relatively easy to
do, so we think they have the potential to be useful tools for identification
of places or population subgroups with higher vulnerability."
The
novel coronavirus SARS-CoV-2 has infected nearly 27 million people around the
world, of whom some 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 at home, and wearing masks and maintaining
social distancing while in public. Yet there hasn't been a good way to monitor
whether -- and among which groups -- such practices are being followed.
Solomon and colleagues, including first author Steven Clipman, a PhD candidate in the Bloomberg School's Department of International Health, quickly accessed willing survey participants via a company that maintains a large nationwide pool of potential participants as a commercial service for market research.
The 1,030
people included in the study were all living in Maryland, which has logged more
than 113,000 SARS-CoV-2 confirmed cases and nearly 3,700 confirmed deaths,
according to the Maryland Department of Health.
The
researchers asked the survey participants questions about recent travel outside
the home, their use of masks, social distancing and related practices, and any
confirmed infection with SARS-CoV-2 either recently or at all.
The
results indicated that 55 (5.3 percent) of the 1,030 participants had tested
positive for SARS-CoV-2 infection at any time, while 18 (1.7 percent) reported
testing positive in the two weeks before they were 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, an infection history was about
4.3 times more common among participants who stated that they had used public
transportation more than three times in the prior two weeks, compared to
participants who stated they had never used public transportation in the
two-week period.
An
infection history also was 16 times more common among those who reported having
visited a place of worship three or more times in the prior two weeks, compared
to those who reported visiting no 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 meal.
Conversely,
those who reported practicing social distancing outdoors "always"
were only 10 percent as likely to have a SARS-CoV-2 history, compared to those
who reported "never" practicing social distancing.
An
initial, relatively simple analysis linked many other variables to SARS-CoV-2
infection history, including being Black or Hispanic. But a more sophisticated,
"multivariable" 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, a lot of
those simple associations went away, which provides evidence that social
distancing is an effective measure for reducing SARS-CoV-2 transmission,"
Clipman says.
The
data indicated a greater adoption of social distancing practices among some
groups who are especially vulnerable to serious COVID-19 illness, suggesting
that they were relatively aware of their vulnerability. For example, 81 percent
of over-65 participants reported always practicing social distancing at outdoor
activities, while only 58 percent of 18-24 year olds did so.
The
results are consistent with the general public health message that
mask-wearing, social distancing, and limiting travel whenever possible reduce
SARS-CoV-2 transmission. The researchers suggest, though, that studies such as
these, employing similarly rapid surveys of targeted groups, could also become
useful tools for predicting where and among which groups infectious diseases
will spread most quickly.
"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 infection risk
with social distancing -- and a month later a large proportion of the
SARS-CoV-2 infections detected in Maryland was among younger people," says
Solomon. "So, it points to the possibility of using these quick,
inexpensive surveys to predict where outbreaks are going to happen based on
behaviors, and then mobilizing 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.
Support
for the research and for some of the individual researchers came from the Johns
Hopkins COVID-19 Research Response Program, the Burroughs Wellcome Fund, and
the National Institutes of Health (DP2LM013102, DP2DA040244).
