These are the findings of a study conducted in France, where it was found that people with the flu are contagious for one day after symptoms begin, and only 5 percent of patients are infectious for more than three days .
"We're finding that patients have very little infectivity four days after the first symptoms appear, so from that point it is safe to return to a normal life," said study researcher Anne Cori, Université Pierre et Marie Curie in Paris, studying the spread of infectious diseases.
Infectivity is the ability of an individual to infect another person if that is vulnerable to the virus.
Previous studies have estimated the infectious period of the flu could be between 1 and 8 days. According to the Centers for Disease Control and Prevention (CDC), people are contagious until five to seven days after onset of symptoms.
This latest research studied the information collected from laboratory experiments in which some people were infected with influenza. The amount of virus in the nose of each person at any time is used to determine how were contagious. This information is associated with a mathematical model to simulate the propagation of the disease.
The study also found that people who have flu symptoms should be isolated quickly to prevent disease transmission.
Researchers estimate that in the best case, a sick person could reduce the number of people it infects by 50 percent if it is isolated or treated within the first 16 hours of symptoms.
This course assumes that people are not contagious until symptoms appear - an assumption that is sometimes made for research purposes, but that is not always true in the real world. In fact, most healthy adults can infect others one day before symptoms appear.
In practice, and as a general rule, we advise people with flu to stay home until 24 hours after the fever is gone.
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