Based on our analysis
of publicly available
data, the current
recommendation
of 14 days for
active monitoring
or quarantine is
reasonable, although
with that period some
cases would be missed
over the long-term.”
airborne isolation standards including
respiratory protection and include
routine systematic environmental
cleaning and disinfection of patient care
areas and surrounding environments.”
Study Estimates 5.1 Days for
Incubation Period
An analysis of publicly available data
on infections from the new coronavirus,
SARS-CoV-2, that causes the respiratory
illness COVID-19 yielded an estimate
of 5.1 days for the median disease
incubation period, according to a study
led by researchers at Johns Hopkins
Bloomberg School of Public Health. This
median time from exposure to onset
of symptoms suggests that the 14-day
quarantine period used by the Centers
for Disease Control and Prevention (CDC) for individuals with
likely exposure to the coronavirus is reasonable.
The analysis suggests that about 97.5 percent of people
who develop symptoms of SARS-CoV-2 infection will do so
within 11.5 days of exposure. The researchers estimated that
for every 10,000 individuals quarantined for 14 days, only
about 101 would develop symptoms after being released
from quarantine.
The findings were published March 9, 2020 in the journal
Annals of Internal Medicine.
For the study, the researchers analyzed 181 cases from
China and other countries that were detected prior to
February 24, were reported in the media, and included likely
dates of exposure and symptom onset. Most of the cases
involved travel to or from Wuhan, China, the city at the
center of the epidemic, or exposure to individuals who had
been to Hubei, the province for which Wuhan is the capital.
The CDC and many other public health authorities
around the world have been using a 14-day quarantine or
active-monitoring period for individuals who are known to
be at high risk of infection due to contact with known cases
or travel to a heavily affected area.
“Based on our analysis of publicly available data, the
current recommendation of 14 days for active monitoring
or quarantine is reasonable, although with that period some
cases would be missed over the long-term,” says study senior
author Justin Lessler, an associate professor in the Bloomberg
School’s Department of Epidemiology.
The global outbreak of SARS-CoV-2 infection emerged
in December 2019 in Wuhan, a city of 11 million in central
China, and has resulted in more than 100,000 officially
confirmed cases around the world and 3,282 deaths from
pneumonia caused by the virus, according to the World Health
Organization’s March 5 Situation Report. Most cases are
from Wuhan and the surrounding Hubei province, although
dozens of other countries have been affected, including the
U.S., but chiefly South Korea, Iran, and Italy.
An accurate estimate of the disease incubation period
for a new virus makes it easier for epidemiologists to gauge
the likely dynamics of the outbreak and allows public health
officials to design effective quarantine and other control
measures. Quarantines typically slow and may ultimately stop
www.healthcarehygienemagazine.com • april 2020
the spread of infection, even if there are some outlier cases
with incubation periods that exceed the quarantine period.
Lessler notes that sequestering people in a way that
prevents them from working has costs, both personal and
societal, which is perhaps most obvious when healthcare
workers and first responders like firefighters are quarantined.
The new estimate of 5.1 days for the median incubation
period of SARS-CoV-2 is similar to estimates from the earliest
studies of this new virus, which were based on fewer cases.
This incubation period for SARS-CoV-2 is in the same range
as SARS-CoV, a different human-infecting coronavirus that
caused a major outbreak centered in southern China and
Hong Kong from 2002 to 2004. For MERS-CoV, a coronavirus
that has caused hundreds of cases in the Middle East, with
a relatively high fatality rate, the estimated mean incubation
period is five to seven days.
Human coronaviruses that cause common colds have
mean illness-incubation periods of about three days.
Lessler and colleagues have published an online tool that
allows public health officials and members of the public
to estimate how many cases would be caught and missed
under different quarantine periods.
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