DAKAR, Senegal — An Italian contractor who flew into Nigeria from Milan became sub-Saharan Africa’s first confirmed coronavirus patient on Friday, stoking concern that an outbreak on the continent could overwhelm already strained health care systems.

The patient, a young man, had no symptoms when he landed this week in Lagos, traveled 60 miles north to the cement factory where he works and developed a fever there, a Nigerian health commissioner said to reporters.

The appearance of the first case in Lagos — a city of 20 million people and the economic capital of Africa’s most populous nation — set off fear, rumors and panicked buying of hand sanitizer and face masks. It also posed a test for the Nigerian medical system, which like others in Africa, has been preparing for the virus to arrive for weeks.

“I feel scared,” said Karo Otitifore, an elementary schoolteacher waiting at a bus stop in Yaba, the Lagos suburb where the Italian patient was being treated. “I try to sit tight, squeeze my whole body so that I won’t have to have too much body contact with people.”