Photo: Karim Sahib Agence France-Presse
The study seems to contradict some of the measures already put in place, such as the search for people in contact with a positive case, because it was only at the time when the symptoms began.
The people infected by the COVID-19 may transmit the virus several days before onset of first symptoms, according to a new modeling study to be published Wednesday.
It comes at a time when several countries are strengthening measures to contain the pandemic.
The study seems to contradict some of the measures already put in place such as ” contact tracing “, that is, the search of persons in contact with a positive case, because it was only at the time when the symptoms began.
“Criteria more inclusive need to be taken into account in the “contact tracing” to identify modes of transmission potential of two or three days before the onset of symptoms and thus be able to control the epidemic more effectively “, said the authors of the study published in the monthly journal Nature Medicine.
The researchers compared clinical data on the excretion of the virus in patients admitted to a hospital in Canton (China) with other data on ” the transmission of peer-to-peer “, where one assumes that one person has infected another, in order to draw conclusions about the period of contagion.
The research team co-led by Eric Lau, University of Hong Kong, has conducted sampling of the throat 94 of these patients and measured the degree of contagion from the first day of symptoms and for 32 days.
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It was found that patients, none of whom was in a serious condition or critical, were infected with the highest viral load after the onset of symptoms, and then decline gradually.
The study is based on public data of 77 transmissions of peer-to-peer, in China and in the world, to assess the amount of time that elapses between the onset of symptoms in each patient.
The researchers assumed that the incubation period was a little over five days.
The authors concluded that infectivity has started 2,3 days before the onset of symptoms and reaches its peak at 0.7 day before the first signs of the disease.
According to the study, 44 % of secondary cases in chains of transmission have been infected during the period of pre-symptomatic. As to the degree of contagion, it would decrease rapidly in seven days.
Commenting on this study, Babak Javid, the school of medicine of the University of Tsinghua, in Beijing, has estimated that these results have “important implications” on the measures of control, such as the question of whether asymptomatic persons should wear a mask.
“This is important because currently the control measures recommended for example by the WHO and the british government are based on the assumption that the contagion maximum occurs after the onset of symptoms and this is one of the reasons why wearing a mask is not recommended for asymptomatic individuals “, he added.
In early April, China announced that it had identified more than 1,300 cases of people infected but asymptomatic. And according to the u.s. Centers for control and prevention of diseases (CDC), a quarter of those infected were asymptomatic.