The novel coronavirus began circulating in Brazil the first week of February, more than 20 days before the first case was diagnosed during Carnival. A study by Fiocruz's Instituto Oswaldo Cruz concluded this by using a methodology based on the death records by Covid-19.
The first case of the disease was identified on February 25, in a traveler who returned from Italy to SÃ£o 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.
To investigate the onset of the outbreak, it is ideal to find virus genomes found in patient samples. However, this methodology could not be applied due to the short time since the beginning of the pandemic and the limited amount of available genomes.
Thus, the researchers developed a new method, using death records to identify the beginning of the transmission, as a "delayed" tracker. This is because the average time between infection and death by Covid-19 is about three weeks.
Translated by Kiratiana Freelon