Coronavirus: What Is Contagion By a “close Contact”?

US authorities have taken drastic measures, such as quarantining residents returning from China and temporarily banning entry to foreigners who have traveled to the affected Chinese regions. At the same time, they have asked most of the country’s residents to live normally.

But there are exceptions. Those who returned from China on or after February 3, have been imposed a quarantine or asked to stay at home. And, discreetly, public health officials at the local level strive to identify “close contacts” of people with confirmed cases of the virus, called 2019-nCoV, to propose a home quarantine and follow them up.

But what exactly is a “close contact” or close? It seems obvious, but it has a clinical definition that varies according to the infectious disease. The deadly measles virus, for example, can remain in one place for hours, in the air and on the surfaces, after an infected person has spent time there. Coronaviruses are usually transmitted by droplets, which requires close physical contact with a sneeze or other body secretion.


The way in which a virus is spread and the severity of the disease it causes determines the way in which public health departments decide how many people are at risk of contagion and how many resources go to social communication.

When it comes to measles, officials give wide publicity to all known places that an infected person has frequented in the days prior to their diagnosis, and they try to locate people who came into contact with that patient and have not been vaccinated.

Various definitions of “close contact”

For the new coronavirus, the guidelines of the Centers for Disease Control and Prevention (CDC) define as “close contact” anyone who has been within six feet of a person infected with the virus for a “prolonged period of time” , as well as those who have had direct contact with the secretions of the infected person. These guidelines are then interpreted by local public health departments.

The European Union health agency offers a descriptive definition: someone who lives in the same home as a patient; someone who has had face-to-face contact or has been in a closed environment with a patient; or a health worker who takes care of a patient directly. Also included is the passenger of an airplane (and by extension, of a train or bus) sitting at a distance of two seats, in any direction, of an infected person.

The World Health Organization identifies health care providers and family members, as well as any person who has been within a meter of a confirmed case, once the infected person has presented symptoms.

Applying these guidelines to real people and to their daily movements is what public health departments across the country do for any infectious disease. Local researchers work with patients to find out where they were and what they did in the days before the diagnosis. They identify anyone who may be at risk of infection, find it and help control their health. Depending on how close the contact was, health officials may ask you to stay temporarily away from others.

Low risk in the United States

The latest official figures indicate that 1,016 people have died and 42,638 were infected in China. But in the United States, there have been only a dozen cases so far, almost all among people who had just returned from a country with 1.4 billion inhabitants. State and federal health officials stress that the risk of contracting the virus here remains low.

Santa Clara County in California has reported two confirmed cases of the virus, both in people who recently traveled to China. Anyone who has lived with one of those people would be considered high risk, said Dr. Sarah Rudman, a county public health official.

Special attention is also paid to health workers. Li Wenliang, the 34-year-old doctor from Wuhan (China), where the outbreak began, raised the alarm about the virus after several cases appeared in the hospital where he worked. He finally contracted the disease and died on February 6, according to the hospital. Many other health workers in China have also contracted the virus, according to authorities.

Case by case

Decisions must be taken on a case-by-case basis to assess risk, Rudman said. The fact that a health professional wore gloves, a mask or other protective equipment, and the type of interaction he had with the patient, are influencing factors.

Some research is easier than others. A newly diagnosed case of coronavirus in Wisconsin involved someone who arrived by plane from Beijing, went directly to a clinic with a mask and has been isolated at home since then, according to the Madison and Dane County Department of Public Health.

The previous cases were not so simple. One factor that has made investigations complicated is the confusion about whether the virus can be spread by an infected person who shows no symptoms. Health departments say that, given the uncertainty, they are taking a cautious approach and looking for any contact that goes back three days before the symptoms began. “Fortunately, we have few cases, so we can do this,” Rudman explained.

As for the rest of us, it is believed that casual contact with an infected person, such as crossing the street or being briefly in the same room does not pose much risk, although CDC officials stress that there is still much to learn about the new virus

And the best protection in those cases can also avoid other undesirable visitors at this time of year: the flu and colds. The latter are often the result of four other coronaviruses that are responsible for a good part of winter diseases.



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