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The circulation of the new coronavirus in the country began in the first week of February, more than 20 days before the diagnosis of the first case and during Carnival. This is the conclusion of a study carried out by the Oswaldo Cruz Institute of Fiocruz, which uses a methodology based on the Covid-19 death records.
The first case of the disease was identified on February 25, in a traveler who returned from Italy to São Paulo. On March 13, the first official confirmation of community transmission occurred, when it is no longer possible to trace the origin of the virus.
Ideally, to investigate the onset of the outbreak, have a representative volume of virus genomes found in patient samples. However, this methodology could not be applied due to the short time elapsed since the start of the pandemic and the limited number of genomes available.
Therefore, the researchers developed a new method, using death records to identify the start of transmission, as a “delayed” tracker. This is because the average time between Covid-19 infection and death is approximately three weeks.
“By looking at the two countries where there are already a large number of sequenced genomes, China and the United States, we discovered that the estimate obtained from the number of deaths was similar to that obtained from the genetic analysis, validating the new approach,” says Daiana Mir , a researcher from Udelar (University of the Republic), Uruguay, who participated in the study.
Other evidence also indicates that local transmission of the virus in the country began in early February. According to InfoGripe, the Fiocruz system that monitors hospitalizations for patients with SARS (Severe Acute Respiratory Syndrome), molecular analysis detected a case of infection with the new coronavirus between January 19 and 25. The sustained increase in the number of infections was observed between February 2 and 8.
The study shows that the circulation of the virus began before control measures were implemented, such as the restriction of air travel and social distance.
“This rather long period of hidden community transmission draws attention to the great challenge of tracking the spread of the new coronavirus and indicates that control measures must be taken, at least as soon as the first imported cases are detected in a new geographic region. ”Says the researcher at the IOC / Fiocruz Molecular Immunology and AIDS Laboratory, Gonzalo Bello, research coordinator.
The researchers also point out that the results warn about the importance of implementing permanent molecular surveillance actions, since the new coronavirus may again generate outbreaks in the coming years.
“Intense virological surveillance is essential to detect possible early reappearance of the virus, informing contact monitoring systems and providing evidence to carry out appropriate control measures,” says Bello.
The study was carried out by the Molecular Immunology and AIDS Laboratory of the IOC / Fiocruz in collaboration with Fiocruz-Bahía, Ufes (Federal University of Espírito Santo) and Udelar, in Uruguay.
