DUBAI, United Arab Emirates (CNN) — How do you know if someone is a carrier of the infection? For viruses such as corona, influenza, respiratory syncytial virus, or the common cold, what is the average time it takes to spread the infection to others? What precautions should the affected person take at school, work and home?

That’s according to CNN medical expert Dr. Lena Wen, an emergency physician and professor of health policy and management at the George Washington University’s Milken Institute School of Public Health, who previously served as Baltimore City’s health commissioner.

CNN: Is there an easy way to find out if someone is infected after contracting the virus?

Dr. Lena Wen: Not really. For many viruses, an infected person can become infected before symptoms appear.

There are some tests that can tell if you have the virus, but they aren’t good enough after infection. The only exception is Covid-19. According to the US Centers for Disease Control and Prevention, a person whose symptoms improve and the result is negative after two at-home coronavirus tests within 48 hours can end the isolation.

One of the more complicating factors is that many people may continue to suffer from symptoms after the infectious period has ended, such as a cough, but these do not necessarily reflect ongoing infection or risk to others.

CNN: On average, if you have a common virus like the coronavirus, the flu, respiratory syncytial virus or the common cold, how long, on average, can you spread the virus to others?

Dr. Lena Wen: Let’s look at these one by one. The virus that causes Covid-19 (SARS-CoV-2) is spread by infected individuals who do not exhibit typical symptoms such as cough, fever, runny nose and sore throat. This person can be contagious just like the person with symptoms.

Scientists estimate that the peak infectious period of SARS-CoV-2 is within 48 hours of the onset of symptoms and in the first five days thereafter. The US Centers for Disease Control and Prevention recommends that someone with Covid-19 self-isolate for five days and wear a high-quality, well-fitting mask when around others for the next five days. .

For influenza, asymptomatic transmission is less common. Although it can spread before symptoms appear, the period of maximum infectivity is thought to be three to four days after the onset of illness.

Respiratory syncytial virus has a long infectious period. People with RSV, the most common respiratory infection thought to affect nearly every child by age 2, are usually infectious for three to eight days after symptoms appear, and transmission is possible before symptoms appear, according to U.S. Centers for Disease Control and Prevention. Disease Control and Prevention. Some children and immunocompromised people can continue to spread the virus for up to four weeks after symptoms stop appearing.

As for the common cold, more than 200 viruses can cause it. The duration of infection depends on the virus and the health of the infected person, but generally follows a pattern similar to that of other viruses.

CNN: What precautions should people with cold-like symptoms take at school and in the workplace, given the potential for long-term infection?

Dr. Lena Wen: Schools and workplaces have long recognized that it’s unrealistic to ask people to stay home until the time they can spread the virus has passed. Although they have policies that require people to stay out of school or work for two to four weeks after symptoms disappear, asymptomatic or pre-symptomatic transmission can spread the virus.

Since children experience an average of six viral respiratory infections per year, compared to two to four for adults, these types of policies can lead to many disabilities that affect children’s learning and development.

CNN: What can people do to reduce the spread to their neighbors?

Dr. Lena Wen: It’s tough. Parents of young children know that their children often get sick because it is very difficult to avoid infection when you are in close contact with them.

The key is to identify those in the household who are most at risk for serious consequences if infected with these viruses. If someone is elderly and has serious medical conditions, it makes sense to separate the affected person from that person. These two people should not eat together or stay in the same room for at least a week after symptoms appear.

It is very difficult to avoid this viral infection, but I want to emphasize that prevention methods work. Wash your hands or use hand sanitizer frequently. Make sure you get your vaccinations regularly, including the updated Covid-19 vaccine, the flu vaccine and the new RSV vaccine for people 60 and older. Importantly, these vaccines reduce the risk of serious illness and reduce your chance of contracting these specific viruses.