The health department of the state of Espirito Santo, Brazil, announced on Tuesday that the presence of IgG antibodies, specific for SARS-CoV-2 virus, was detected in serum samples from December 2019.
The health department said that 7,370 serum samples had been collected between December 2019 and June 2020 from patients suspected of being infected with dengue and chikungunya.
With the samples analyzed, IgG antibodies were detected in 210 people, of which 16 cases suggested the presence of the novel coronavirus in the state before Brazil announced the first officially-confirmed case on Feb. 26, 2020. One of the cases was collected on Dec. 18, 2019.
The health department stated that it takes about 20 days for a patient to reach detectable levels of IgG after the infection, so it could have occurred between late November and early December 2019.
The Brazilian Ministry of Health issued a notice on the same day, instructing the state to conduct in-depth epidemiological investigations and send serum samples to Oswaldo Cruz Foundation, Rio de Janeiro, for RT-PCR test.
"Only with confirmation by the reference laboratory and the deepening of epidemiological studies will the Ministry of Health be able to confirm, or not, whether these cases were really positive for SARS-CoV-2," said the ministry.