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The entire period of viral infection can be simply divided into three periods: incubation, clinical infection, and recovery.
During the incubation period, the virus attaches itself, enters, multiplies, and spreads to other cells in the airways. However, the infected person still does not feel any symptoms. The incubation period for SARS-CoV-2 infection is up to 14 days (mean 5 days) from contact with a human subject. It is important to mention that at the end of the incubation period, when the person still does not feel anything, the virus is already spreading from their respiratory tract to the environment and can infect others.
During the period of clinical infection, the virus continues to actively multiply in the cells of the respiratory tract and can spread to other organs. This causes tissue damage and an immune system reaction, which is accompanied by clinical symptoms. During this period, the person spreads the virus in the environment by breathing, talking, coughing, or sneezing. This period can be prolonged due to complications of the disease. But over time, the spread of the live virus stops, although symptoms can still continue.
There is evidence that presymptomatic spread of the virus can infect up to 12.6% of all infections, says Dr. M. Tomkuvienė.
During the third recovery period, viral genetic material may still be found in the airways, but there is no active spread of the virus and the patient’s symptoms subside. However, residual phenomena such as coughing, feeling weak, etc. they can go on for a long time.
“At the end of the incubation period, there is a short but epidemiologically very dangerous period in which the human respiratory tract releases enough virus to infect others, but the carrier himself still does not feel the symptoms”, says Dr. Miglė Tomkuvienė, biochemist of the VU Life Sciences Center. – According to the scientific literature, in the case of SARS-CoV-2 this period is approximately 1-3 days. There is evidence that presymptomatic spread of the virus represents up to 12.6% of all infections. “
Much is now known about how long a person infected with SARS-CoV-2 can infect others. A systematic review and meta-analysis by The Lancet Microbe was published on November 19 to examine how long a person carrying SARS-CoV-2 or COVID-19 has a live virus in their respiratory tract.
Photo / schedule of “Wait, Doctors”
Dr. Miglė Tomkuvienė says that the viability of the virus was checked by culture: whether the virus isolated from the patient sample can continue to multiply in the cells grown in the laboratory. If so, that patient’s cells are still producing infectious virus particles, and that person can infect others. An analysis of 79 studies involving 5,340 people infected with the SARS-CoV-2 virus showed that none of them shed the potentially infected virus for more than 9 days after the onset of symptoms. It should be noted that we are talking here about a mild to moderate form of Covid-19 disease.
“Interestingly, even after recovery from COVID-19 infection, PCR can detect small amounts of viral genetic material in human airways for a long time, even 8 weeks after recovery. It’s like a trace left by the virus, ”says Ugnė Ringelevičiūtė, Senior Resident Physician at the VUL SK Center for Hematology, Oncology and Transfusion.
Sigismund Gedvila investigation / 15min photo / COVID-19
Based on these data, the isolation rules state that in patients with the mild form of Covid-19, isolation can be interrupted 10 days after the onset of symptoms if symptoms persist in the last 24 hours. no fever occurred. No repeat PCR tests required.
U.Ringelevičiūtė emphasizes that less often, although hospitalization is not required, symptoms such as fever can last longer. With such a severe course of the disease, there is a minimal chance of infecting those around you. Therefore, the isolation rules in this case state that if the symptoms of the disease disappear after the 10th day of illness, the isolation can be terminated at least 3 days after the symptoms have disappeared. In any case, the family doctor decides to terminate the isolation.
Long-term exposure to the virus can be seen in the elderly, immunosuppressed, and seriously ill. A Chinese study, published in The Lancet Infectious Diseases, found that seriously ill people excreted significantly more virus in their airways and survived longer than the mildly ill group.
In patients who required hospitalization, the infectious virus was isolated for an average of 8 days and a maximum of 20 days. An American and British publication reports that an immunosuppressed patient with a blood disease with the asymptomatic form of SARS-CoV-2 secreted the live virus up to 70 days after onset of the disease, but these cases are specific and extremely rare cases in the practice.
Patients with severe illness who develop pulmonary fibrosis may experience shortness of breath and coughing for the rest of their lives, says U. Ringelevičiūtė.
However, even after overcoming a period of active infection, certain symptoms such as coughing, loss of smell and taste, or expressed general weakness may persist for a longer period of time.
“These are the residual phenomena of the disease, when the damaged structures (lung tissue, nasopharyngeal epitheliocytes, etc.) have not recovered. The infected person no longer spreads the virus, although the residual effects may be felt long enough. Patients with serious illnesses who develop pulmonary fibrosis may experience shortness of breath and coughing for the rest of their lives, ”says U. Ringelevičiūtė.
Early studies have shown that the proportion of asymptomatic people can go up to 81%, but according to a recently published meta-analysis, the potential proportion of asymptomatic people is only around 17% (4-41% in different studies). All the others, who were counted as asymptomatic vectors, were shown to be presymptomatic, that is, after transmitting the virus to another person, they themselves subsequently experienced symptoms.
Asymptomatic carriers of the virus can infect others less frequently than the sick. It is not known exactly how long asymptomatic people can spread the virus that can infect another person. When we detect the SARS-CoV-2 virus in the airways of an asymptomatic patient using PCR, we do not know if the person will have symptoms in the near future. In either case, isolation is required. Isolation rules state that in patients with an asymptomatic form of COVID-19, isolation can be terminated after 10 days. after PCR detection of Sars-Cov-2 when the virus was first detected in a nasopharyngeal sample.
To promote a culture of open data and research, the authors will publish material errors, corrections or changes of opinion or interpretation found in this text here. There you can also find a list of used scientific sources.
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