The Centers for Disease Control and Prevention have new guidelines that clarify what exactly “close contact” means when it comes to transmission of SARS-Cov-2, the virus that causes COVID-19.
Previous guidelines suggested that a close contact occurs when a person is within 6 feet of an infected individual for 15 consecutive minutes. Now, the CDC acknowledges that even brief exposures can lead to transmission. Specifically, the new guidelines suggest that people who spend a total of 15 minutes in contact with an infected person over a 24 hour period should be considered close contact.
Despite the change, most public health experts have been clear for months that there̵7;s nothing magical about six feet away. In the same way, there is nothing magical for 15 minutes. They should be used as a rough estimate to show relatively higher risk exposure types.
This new guide is therefore an important recognition of how easily this virus can spread. It is not a strong reversal of the CDC instructions, like the instructions regarding the mask and the go back and forth testing of people without symptoms.
This change reflects new evidence that has emerged. This change is an example of how science works. As an epidemiologist studying respiratory viral transmission, I don’t really think this change will have a big effect on the way we live in a pandemic, but it does represent further evidence. information about how easily this virus is spread.
The new advice comes after the outbreak investigation is published in the CDC Mortality and Disease Weekly Report. The investigation found that a prison staff member in Vermont was infected, most likely during a series of brief interactions with the infected prisoners but had no symptoms.
Prisoners are waiting for test results in a quarantine unit. Staff reported no close connections other than work and they also did not travel outside of state. At that time, Vermont was experiencing low levels of community contagion. The outbreak investigation used video evidence from surveillance cameras in the prison to record short interactions. Each interaction lasted about one minute, and a total of staff had close contact with infected prisoners for about 17 minutes during the eight-hour shift. For at least some of those interactions, infected prisoners did not wear masks.
The recording of infectious exposures is difficult for respiratory viruses. After all, we can’t see viruses moving through the air. The footage in this case demonstrates pretty solid evidence. And so the CDC is realizing the possibility of shorter interactions posing some risks.
This change is also the acknowledgment that the previous definition made at least one explicit assumption that may not be true. The main assumption of the old rule is that there is an exposure threshold effect. Meaning, once you have been exposed to a certain amount of the virus (value of 15 minutes), your risk of disease will increase. The downside of this assumption is that below that threshold your risk is still low. That’s why we have seen some schools mistakenly move students in a 14-minute period.
The new guidelines show that there are several relationships for response between dose and risk of disease. Meaning, the more exposure you are to the virus, the higher your risk is, even if the exposure didn’t happen at the same time.
What does it mean?
While I don’t think this update will lead to major changes, one thing it does is expand the group of people to follow contacts. In the ideal scenario, this change could mean we detect cases much earlier after exposure. These people can then begin quarantine before they infect and spread to others.
Take, for example, the holidays coming. Leaving a family to Thanksgiving usually means sharing a meal and maybe spending a few hours in close contact with others. It is still a risk, especially since people without symptoms can spread the disease.
Those who attended that meeting were previously considered closely related, and they are still. But now, short interactions that add up over time – with a server at a restaurant, for example – are considered intimate contacts.
This change from the CDC shows that we need to be more careful about short interactions – in the office or at school, for example. We shouldn’t think to ourselves “Just for a minute, I don’t need my mask.” The importance of wearing a mask all the time to protect others has never been more obvious. We may not know that we have been infected and even a brief, undisclosed encounter can spread the virus.
This article is republished from The Conversation under a Creative Commons license. Read the original article.