The Centers for Disease Control and Prevention (Centers for Disease Control and Prevention) has new guidelines that clarify that “close contact” actually refers to the spread of SARS-Cov-2, which is the virus that causes COVID-19.
Previous guidance suggested that close contact will occur when a person is within six feet of an infectious individual for 15 minutes. Now, the CDC recognizes that even brief contact can cause transmission. Specifically, the new guidelines recommend that people who have been in contact with an infected person for a total of 15 minutes within 24 hours should be considered close contact.
Despite the changes, most public health professionals have known for months that there is no magic at six feet. Similarly, about 1
Therefore, this new guide is an important recognition that the virus is easy to spread. It is not a dramatic reversal of the CDC guidelines, like the guidelines related to masks and testing back and forth for asymptomatic individuals.
This change reflects the new evidence that has emerged. This change is an example of how science works. As an epidemiologist who studies the spread of respiratory viruses, I don’t actually think that this change will greatly affect our lives during a pandemic, but it does represent ongoing evidence of how easy this virus is to spread.
After an outbreak investigation was published in the CDC’s “Morbidity and Mortality Weekly Report”, new recommendations were made. The investigation found that a prison staff member in Vermont was infected, most likely after a series of brief contacts with infected but asymptomatic prisoners.
The prisoner waited for the test results in the isolation area. The employee reported that there was no close contact outside of work, and they did not travel outside. The level of community transmission in Vermont was low at the time. The outbreak investigation used video evidence from prison surveillance cameras to record brief interactions. Each interaction lasted about one minute. During the eight-hour shift, the staff stayed in close contact with the infected prisoner for about 17 minutes. For at least some of these interactions, the infected prisoners did not wear masks.
It is difficult to record infectious exposure to respiratory viruses. After all, we cannot see the virus spreading in the air. The video in this case represents quite strong evidence. Therefore, CDC is recognizing the possibility that shorter interactions will bring certain risks.
This change also indicates that the previous definition makes at least one clear assumption that may be incorrect. The main assumption of the old rules is that there is a threshold effect of exposure. In other words, once you are exposed to a certain amount of virus (worth 15 minutes), your risk of illness will increase. The flip side of this assumption is that at a level below this threshold, your risk is still low. This is why we have seen some schools mistakenly take students away every 14 minutes.
The new guidelines indicate that there is more dose-response relationship between virus exposure and disease risk. In other words, even if you are not exposed all at once, the more viruses you are exposed to, the higher the risk.
What does it mean?
Although I don’t think this update will bring major changes, one of the things it does is to expand the pool of people used for contact tracking. Under ideal circumstances, this change could mean that we detect more cases as soon as possible after contact. These people can isolate it before the infection starts and then spread it to other people.
Take the upcoming holiday as an example. Thanksgiving as a family usually means sharing a meal and possibly spending hours in close contact with others. This is still a risk, especially because those without symptoms can spread the disease.
The people attending the party were considered intimate contacts before, and they still do. But now, short-lived interactions over time (for example, interaction with a server in a restaurant) will be seen as close connections.
The changes made by the CDC indicate that we need to be more careful about short-lived interactions, such as in the office or in school. We shouldn’t think to ourselves: “It only takes a minute and I don’t need to wear a mask.” The importance of always wearing a mask to protect others has never been more obvious. We may not know that we have been infected, and even brief, undisguised encounters may have spread the virus.
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