People infected with the new coronavirus can infect others several days before the first symptoms of the covid-19 disease appear, indicates a study published today by the journal Nature Medicine, which advocates an expansion in contact tracking.
One of the measures that is in force in several countries affected by the covid-19 pandemic, such as Portugal, is the tracking of contacts, that is, the search for people who have been in contact with a patient from the moment they tested positive for the new coronavirus, but researchers argue that this universe should be extended to people who had contact in the days before the disease was detected.
“More inclusive criteria must be taken into account when it comes to tracking contacts, in order to identify possible outbreaks of transmission within the two or three days prior to the onset of symptoms”, stress the study authors, stressing that this will allow “controlling the epidemic more efficiently ”.
To reach this conclusion, the team of researchers, co-directed by Eric Lau, from the University of Hong Kong, compared clinical data on the spread of the virus in patients admitted to a hospital in Guangzhou, southern China.
The research led to the collection of throat samples from 94 patients, and the degree of contagion of the virus was measured from the first day of symptoms and for 32 days.
The finding is that patients, none of whom were in a serious or critical condition, had the highest viral load as soon as symptoms appeared, before gradually subsiding.
The study also used public data from 77 “point-to-point” transmissions in China and other countries to assess the time between onset of symptoms in each patient to come to the conclusion that the incubation period is just over five days. .
It was also concluded that the infection appeared between two to three days before the first symptoms appeared, reaching the peak of transmission capacity 0.7 days before the first signs of the disease.
The researchers further concluded that 44% of secondary cases in the transmission chains were infected during the pre-symptomatic period.
Globally, the covid-19 pandemic has already claimed almost 127,000 deaths and infected more than two million people in 193 countries and territories. More than 428,000 patients were considered cured.
In Portugal, 599 people died of the 18,091 registered as infected.
The disease is transmitted by a new coronavirus detected in late December in Wuhan, a city in central China.
To fight the pandemic, governments sent four billion people home (more than half the world’s population), closed non-essential trade and drastically reduced air traffic, paralyzing entire sectors of the world economy.
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