COVID-19: How long does a person spread before showing symptoms

Patients with COVID-19 disease may begin to expel or excrete the infective coronavirus two to three days before the first symptoms appear, according to a study published in the scientific journal Nature Medicine.

Currently, infection control and spread measures are based on the time elapsed between cases in a chain of transmission (serial interval) and the incubation period (time from infection to the appearance of symptoms in a patient).

If the serial interval is less than the incubation period, this indicates that transmission may have occurred before symptoms develop, and therefore the control measures being applied may not be correct.

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To improve them and prevent the spread of the infection, Eric Lau, a researcher at the University of Hong Kong, and his colleagues studied the temporal patterns of the spread of the virus in 94 patients with COVID-19 admitted to the Eighth People's Hospital in Guangzhou, China. .

The researchers collected samples from the throat of these patients from the time the symptoms appeared until 32 days later and found that the patients had the highest viral load at the onset of symptoms.

In a parallel study based on publicly available data, scientists analyzed the COVID-19 transmission profiles of 77 patient pairs (transmission pairs) with a clear epidemiological link, that is, with a high probability that one had infected the other.

From these data, the researchers deduced that the contagion had occurred two to three days before symptoms appeared. The authors caution, however, that the study uses patient recall of symptom onset, which may bias the information.

Source: EFE