Perhaps we have all heard a sick person, with the flu or a cold, for example, say: “don’t worry, I am no longer contagious.”
Because there is a belief that some viruses only spread when they are incubating, that is, during the period that passes from when you become infected with the virus until the first symptoms appear.
The belief, however, is wrong.
Many viruses continue to spread later that the symptoms of the infected person disappear.
That is, a cough or fever are not the only indicators that a person can infect others with a virus.
And what about the new SARS-Cov-2 coronavirus that has been shown to have unique characteristics that were not known in any other pathogen?
How long does its contagiousness last?
And how can infections be avoided when a person infected with the coronavirus has no symptoms?
Since SARS-Cov-2 was detected in China last December, several scientific teams have been investigating the incubation period of the new coronavirus.
One such study, conducted by researchers at the Johns Hokpins School of Public Health and published in Annals of Internal Medicine in May, it found that the average incubation period of the new coronavirus is 5,1 days.
And the majority (97.5%) of those infected who develop symptoms they do so within a period of 11.5 days.
“From the time a person is exposed to the virus through the nose or mouth, it takes an average of three days until they begin to develop symptoms, such as cough and fever,” doctor Vicente Soriano, a specialist in diseases, explains to BBC Mundo. infectious diseases and clinical genetics and former adviser to the World Health Organization.
“But the ability to infect others, to transmit that virus to others extends from 7 10 more days“explains the expert, who is also a professor at the International University of La Rioja, Spain.
He adds that from that moment on, when the symptoms have already subsided or disappeared, the possibility of infecting others also decreases.
The expert emphasizes, however, that PCR tests, which are used to detect the virus, they can continue to test positive for several days or weeks after infection with the virus.
But this does not mean that the person is still contagious.
“The PCR that detects fragments of the virus genome can remain positive after one, two or even three weeks after the person has been cured of covid”, points out Vicente Soriano.
“But that positive PCR does not reflect contagiousness. What the PCR detects are virus fragments, or ‘junk sequences’, which are fragments of the virus genome that are in the respiratory tract and that we expel for several weeks after the disease has been cured, “explains the expert.
Indeed, the sensitivity of diagnostic tests is a problem that has been known since they began to be applied and illustrates why the statistics of covid-19 are far from perfect.
But as Dr. Vicente Soriano emphasizes, “the contagiousness of the coronavirus is basically 7 to 10 days, one or two days before the symptoms start and while the symptoms occur,” he adds.
- 10 days after the onset of symptoms Y
- 24 hours without fever and without using fever-reducing medications Y
- When other symptoms of covid-19 are improving
But what happens when a person is infected with the coronavirus and has no symptoms? How to know that it will not infect others?
A study published in August in Journal of the American Medical Association (JAMA) found that close to 30% of patients who test positive for the coronavirus are asymptomatic.
And the researchers found that despite not having symptoms, patients are carriers of the same amount of virus as patients with symptoms and both remain with that viral load for the same time.
Therefore, experts point out, the importance of wearing masks and observing social distancing.
These two measures can help reduce the risk that a person with Covid-19 and asymptomatic infects other people.
“With asymptomatic patients it is not known for how long they can be contagious,” explains Vicente Soriano.
“Basically, asymptomatic people can transmit viruses to others for a week, just like those with symptoms, but unless the person has an antigen test (to detect that they had the disease) or a PCR, that person goes unnoticed“, says the expert to BBC Mundo.
“Hence the interest in screening to identify people who may have been in an area of contagion with people who have not yet tested positive and do the antigen test or PCR, starting 48 hours after the event.
In this way, says the expert, the asymptomatic can be identified and kept isolated for 10 days to avoid other infections.
When a person had symptoms, it is not necessary to perform the screening test again, it is enough that they remain isolated for 10 days to stop being contagious.
These recommendations, however, do not apply to people who had more severe symptoms of COVID-19 and were not hospitalized.
As pointed out by the Centers for Disease Control and Prevention (CDC) of the United States, in many cases, when a person was seriously ill and was not hospitalized, they will have to stay at home until20 days after the initial onset of symptoms.
Also, people with immune system disorders or weakened immune systems who have had COVID-19 will need to stay home longer and consult their doctor to find out when they can stop isolating themselves.
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