About 50 workers were infected by the novel coronavirus during an outbreak in recent weeks at a production well owned by Brazilian oil firm Dommo Energia SA, two regulatory sources with knowledge of the matter told Reuters.

The production well, at the offshore Tubarao Martelo field, has been paralyzed since early May, added the sources, who requested anonymity to discuss private operational matters.

It was not clear which well was affected, nor how much production it was responsible for.

Representatives from Dommo did not respond to multiple e-mails, phone calls and social media messages seeking comment.

In February, Petro Rio SA, another Brazilian oil firm, agreed to buy a controlling stake in Tubarao Martelo for $140 million, though regulatory filings from recent weeks indicate the operating license has not been formally transferred.

Brazil-listed common shares in Petro Rio fell 2.8% after Reuters divulged the outbreak, though shares were up 1% in afternoon trade amid a broader oil market rally.

Brazil-listed common shares in Dommo, which are lightly traded, were little changed.

In a statement, Petro Rio said it had not registered any coronavirus cases among workers at its own offshore facilities, and had managed to detect nine cases of the virus among workers before they embarked, thanks to rigorous screening measures.

(Reporting by Gram Slattery and Rodrigo Viga Gaier, Additional reporting by Marta Nogueira; Editing by Franklin Paul and Steve Orlofsky)