The 19-year-old woman from the Kokama tribe tested positive for the virus in the district of Santo Antonio do Içá, located near the border with Colombia some 880 km (550 miles) up the Amazon river from the state capital Manaus.
"Unfortunately, we have an indigenous person with the virus," said a Sesait spokeswoman by telephone.
The patient, whose name was not made public, is a medical worker who had traveled upriver to several villages, including the town of Tabatinga, and returned home with fever, a sore throat and chest pains, the O Globo newspaper reported.
Four cases of coronavirus have been confirmed in the same district, including a Brazilian doctor who tested positive last week, raising fears that the epidemic could spread to remote and vulnerable indigenous communities with devastating effect.
The doctor, whose name was not made public, had returned from vacation in southern Brazil to work with the Tikunas, one of the largest tribe in the Amazon with more than 30,000 people who live in the upper Amazon near the borders with Colombia and Peru.
Health experts warn that the spreading virus could be lethal for Brazil's 850,000 indigenous people, who have been decimated for centuries by diseases brought by Europeans, from smallpox and malaria to the flu.Health experts say the indigenous peoples' way of life in communal hamlets under large thatched structures increases the risk of contagion if any single member contracts the virus, which causes the sometimes fatal respiratory disease COVID-19.