COVID-19 has been in the news since early December, but we still have important questions unanswered. How long can it survive on surfaces? How is it really transmitted? How long does it take for symptoms to begin after infection? Johns Hopkins University seems to have answered the last one.
There are other questions that remain unanswered as well. Where did it really come from? Is the BSL-4 research lab in Wuhan, China part of that answer? What about bats and pangolin and snakes and the open air markets across China?
Lots of important questions, to be sure. But the researchers at Johns Hopkins Bloomberg School of Public Health wanted an answer to the incubation question. That one is critical because any effective medical and policy response would need to time quarantines to match the incubation period of the disease and its’ symptoms.
Right now, quarantine periods of 14 days are being used as a standard. But is that enough time to allow for symptom onset? Is it too long?
The Hopkins team set out to review 181 cases of confirmed COVID-19. The cases were from China and several other countries and all were confirmed before February 24. Almost all the cases involved travel to Wuhan or exposure to people who had been to Hubei province, of which Wuhan is the capital.
Their review led them to the conclusion that in 97.5% of all cases, symptom onset will begin within 11.5 days after initial exposure. That makes a 14 day quarantine period reasonable. In fact, they estimate that for every 10,000 people who are quarantined for 14 days after initial exposure, only about 101 will develop symptoms after release from quarantine.
“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 results of the Hopkins research was published March 9 in the journal Annals of Internal Medicine.
The other important finding in their research is their estimation of a mean incubation period. The Hopkins team estimates that the median incubation period is 5.1 days from exposure.
According to official reports, over 118,000 cases of COVID-19 around the world as of this writing. In spite of reports to the contrary, virtually all of the outbreak can be traced back to travel to and from, or exposure to someone who traveled to or from, Wuhan, Hubei Province or somewhere else in China with active cases. For the small remainder of cases, medical and epidemiological professionals are working to establish links to origin.
Accurately estimating the disease incubation period for a novel virus makes it possible for health officials to work to improve outcomes. Epidemiologists can better evaluate the likely dynamics of the outbreak. Public health officials are better able to design effective quarantine measures and develop other means of controlling the spread.
While there will almost always be some anomalous cases where incubation periods last beyond the quarantine, the practice has been shown to slow, and may ultimately halt, the spread of infection.
Of course, quarantines have costs. People are kept away from their livelihoods and families. The economy will suffer somewhat due to reduced personal spending. Additionally, the issue becomes more acute when health care workers, first responders and other key personnel are quarantined.
Of course, society in general might get a big boost and some relief if we quarantine all our politicians. Not so much because they’ve been exposed to COVID-19, but because it might be nice to NOT be exposed to them for a while!
Keep the faith and keep after it!