Nigeria has a third confirmed case of Ebola in the oil hub of Port Harcourt, bringing the country's total confirmed infections to 17, with 271 people under surveillance, the health minister said on Monday.

The figure was revised up from an earlier one of 16, which had been the result of an error in counting.

A doctor in Port Harcourt died last week after treating someone who came in contact of the Liberian-American man who was the first recorded case of the virus in Africa's most populous country. That raised alarm that Ebola, which looked on the verge of being contained in the commercial capital, Lagos, may flare up again elsewhere.

Patrick Sawyer, the first case, came from Liberia, and then collapsed at Lagos airport on July 20.

The shift to Port Harcourt shows how easily containment efforts can be undermined. Nigeria's government acted quickly at the end of July, setting up an isolation ward and monitoring contacts closely. But one of Sawyer's contacts in Lagos avoided quarantine and traveled east to Port Harcourt.

He has since recovered from the disease, but he infected the doctor who treated him, who then himself died of Ebola. A third case in the oil city was a female patient in the same hospital as the doctor and caught the disease from him.

Health Minister Onyebuchi Chukwu said in a press conference that 72 people in Lagos, a city of 21 million people, were still under surveillance. Another 199 people were under surveillance in Port Harcourt.

"Two other contacts of the late Port Harcourt doctor, one of the doctors who managed him and a pharmacy technician working in the doctor's hospital, are symptomatic and have been admitted to the isolation ward in Rivers," Chukwu said, although he added that preliminary tests had been negative for Ebola.

The outbreak of Ebola in West Africa is the world's worst ever. It has killed at least 1,550 people, and the World Health Organization says it could infect 20,000 more.

(Reporting by Camillus Eboh; Writing by Tim Cocks; Editing by Lisa Shumaker; Editing by Larry King)