RIO DE JANEIRO, BRAZIL – The novel coronavirus had been in circulation for at least 20 days in Brazil when crowds took to the streets in major cities to celebrate Carnaval, according to a study released on Monday, May 11th, by the Oswaldo Cruz Institute (IOC/Fiocruz).
The study shows that the Sars-CoV-2 virus began to spread in the country in the first week of February, more than 20 days before the first case was officially diagnosed in a traveler who returned from Italy to São Paulo.
The case was detected on February 26th, Ash Wednesday, almost 40 days before the first official confirmations of community transmission, on March 13th, highlighted O Estado de S. Paulo newspaper.
It is also noted that when the first carnaval blocks took to the streets, community transmission of the disease was already occurring. This was most likely spurred by the crowds. The first cases would date back to late January.
The study was conducted using a statistical methodology of inference, based on official death records, and published in the journal ‘Memórias’ of the Oswaldo Cruz Institute as a preliminary study, with no peer review as yet.
The work also showed that the virus began to spread much earlier than officially recorded in Europe and the United States.
The authors point out that, in all the countries analyzed, the circulation of Covid-19 began long before control measures were implemented, such as air travel restrictions and social distancing.
In Europe, the disease began to spread approximately in mid-January in Italy and between late January and early February in Belgium, France, Germany, the Netherlands, Spain, and the United Kingdom. In New York City, in the United States, the disease started to spread in early February too.
This is the first research to pinpoint the start period of community transmission in Brazil, and reinforces preliminary evidence from research conducted in Europe with genetic analysis. It also corroborates findings from studies conducted in the United States that showed the start of viral spread in New York City occurred between January 29th and February 26th.
Although several countries report the start of community transmission in very close times, the spread of the epidemic in each location seems to have followed its own dynamics.
“In all likelihood, the epidemic spread was defined by local factors such as environmental features like temperature, precipitation and air pollution, population density, and demographics,” adds Tiago Graf, a researcher at the Gonçalo Moniz Institute (Fiocruz-Bahia).
The authors also stress that the results obtained reinforce the significance of implementing permanent molecular surveillance actions, since the novel coronavirus may once again be circulating and lead to outbreaks over the next few years.
“Intense virological monitoring is critical to early detection of a potential re-emergence of the virus,” says Gonzalo Bello, researcher at the AIDS and Molecular Immunology Laboratory of the IOC/Fiocruz, research coordinator.
Technique
To estimate the onset period of community transmission of the novel coronavirus, the researchers developed a new method, based on the exponential growth in the number of deaths in the first weeks of the outbreak.
Since the shortage of diagnostic tests and the high percentage of asymptomatic infections hinder the counting of cases of the disease, death records are considered the most reliable source of data on the progress of the epidemic.
They can be used as a “lagging” tracker, which allows observing the course of the disease retrospectively.
Considering that the average time between infection and death by Covid-19 is approximately three weeks and the mortality rate of the disease is around one percent, scientists have applied a statistical method to infer the time of onset of the epidemic from the cumulative number of deaths in the first weeks of the outbreak in each country.
“Looking at the two countries where there are currently large numbers of sequenced genomes – China and the United States – we found that the estimate based on the number of deaths was similar to that obtained from genetic analysis, confirming the new approach,” says Udelar researcher Daiana Mir.
In Brazil, other evidence supports the estimate that local transmission began in early February, coinciding with the spread of the epidemic in North America and Europe.
According to InfoGripe, a system of the Oswaldo Cruz Foundation that monitors the hospitalization of patients with severe acute respiratory symptoms (SARS), the number of hospitalizations has been above that observed in 2019 since mid-February 2020.
In addition, retrospective molecular analyses of SARS samples detected a case of SARS-CoV-2 infection in Brazil in the fourth epidemiological week between January 19th and 25th.
A sustained increase in infections was observed from the sixth epidemiological week, between February 2nd and 8th, according to Fiocruz’s MonitoraCovid-19.
“These epidemiological data confirm the introduction of Sars-CoV-2 in Brazil since late January and clearly support our results, which suggest that the virus was in circulation among the Brazilian population since early February,” points out Gonzalo.
Source: O Estado de S. Paulo