David Shulkin, MD | December 7, 2020
The CDC’s reported change to recommend the shortening of the quarantine period for people with COVID-19 exposure seems like welcome news. The rationale for this of course is that many more people may be willing to comply with a quarantine if the timeframe is shorter and that may result in an overall reduction of viral transmission.
While CDC’s new recommendations have been widely reported by the media, the agency has as not yet put this on their website. Whether CDC has new data to suggest the scientific basis for changing their recommendation is unclear.
Shortening the time of a quarantine during the height of the pandemic, in the absence of scientific data, is potentially risky. The World Health Organization has warned that doing so may be unwise. WHO cautions that even a slight reduction in the length of a quarantine may significantly raise the risk of viral spread.
It may be that CDC will share new data that will address these concerns. But data published to date suggests reason for caution. The mean incubation period for COVID-19 appears to be 4.5-5.8 days. But even with a mean time under 7 days, in the context of millions of infected patients there are still large numbers that would experience longer incubation times. Approximately 2.5% of patients will develop COVID-19 more than 11 days after exposure. So even at 10 days after exposure, 101 out of every 10,000 exposed patients will develop active infection. With 150,000 new COVID patients each day in the US, this means that approximately 4,500 patients each day will have developed COVID-19 even 10 days after their initial exposure. While the number of people an infected person can infect is variable, some people with COVID can infect hundreds of other people. So 4,500 people can do a lot of damage and that means a quarantine period of less than 14 days represents the potential for significant additional viral spread.
The international experience on quarantines is mixed. In September, France cut its quarantine time after exposure from 14 days to 7 days. Whether it was related to this or not, France has seen a significant increase in infections since the new policy was put into place. China took a different approach and doubled quarantine time to 28 days, although foreign travelers to China are required to keep a 14 day quarantine upon arrival.
David Shulkin, MD
Quarantines after significant exposure are important in controlling the pandemic for a number of reasons. We know that up to 20% of people who are infectious with COVID-19 virus are asymptomatic. According to the CDC, for those patients that do develop symptoms, 12% will still have replication-competent virus after 10 days and 5% will remain infectious after 15 days. For patients with severe COVID-19 active virus can be found up to 20 days after infection.
So what should we think about a new recommendation of a 10 day quarantine after significant exposure and 7 days with a negative test? Without CDC sharing additional scientific data on which this change is based, I have some concern.
It does not seem prudent to shorten a quarantine in areas where there is a high incidence of virus in the community. I have less concern if there is generally a lower level of asymptomatic viral transmission in the community. In communities where the testing positivity rate is 5% or less a reduced quarantine period will be less risky. Maybe this is why CDC is wisely signaling that the new recommendations must be interpreted by local public health agencies. In other words, though the media may be reporting these are new national recommendations, they really are meant to be individualized for the local data in a community. I hope CDC will make that intent clear.
Given the false positive rates of COVID testing in real world settings, it seems imprudent to rely upon a single test for recommending shortening to a 7 day quarantine. It seems more reasonable to suggest that two negative tests should be required to shorten the quarantine to 7 days. The timing of these tests is also critical and should be standardized. Testing has the best predictive value at approximately 3 days after symptom onset or 8 days in total after exposure. Therefore, early testing may lead to more false negatives. If a 7 day quarantine is being contemplated it would be best to get the test at the earliest on day 5 or 6 and then a second test repeated 24 hours later and if both are negative, in the setting of no symptoms, then a shortened quarantine could be considered. This of course required ample testing capacity and short turn around times in the community.
Changing policy recommendations based upon experience and new data is a good thing and CDC has a leadership role in this for the country. But it’s also important for the agency to be transparent with the data on which it is basing these recommendations and be clear on how they should be interpreted and utilized.
Otherwise making changes in the middle of a pandemic can cause more confusion and harm than good.
This article originally appeared on The Shulkin Blog.