The case, the first in sub-Saharan Africa, has prompted fears the virus could spread quickly in Lagos. The densely populated commercial capital of 20 million people is the biggest city in a country of some 200 million inhabitants.

Health experts are concerned about an outbreak in a region where health systems are already overburdened with cases of malaria, measles, Ebola and other infectious diseases.

The Italian man arrived in Lagos on Feb. 24 from Milan on a Turkish Airlines flight that had a connection in Istanbul. The following day he traveled to neighboring Ogun state and was in the country for almost two full days before being isolated.

Asked in a telephone interview about the number of people Nigerian authorities had been in touch with who may have had contact with the man, Lagos state Health Commissioner Akin Abayomi said: “It is around 100 people but that number is increasing every minute.”

The patient works as a vendor for cement company Lafarge Africa Plc (WAPCO.LG) in the southwestern state of Ogun.

“The number is going up all the time as we find people who were on the flight. We found people who were on the journey to Ogun, in contact with him at the factory and people at the hotel,” Abayomi said.

Health Minister Osagie Ehanire, speaking on Nigerian TV, said the man was responding to treatment and seemed to be “on the way to recovery”.

President Muhammadu Buhari’s spokesman, in a statement issued late on Sunday, called for calm.

“President Buhari urges Nigerians not to panic about the news of this first case of Covid-19 in our country, as undue alarm would do us more harm than good,” said the statement.

Lafarge issued a statement on Sunday in which it said its cement production lines remained open. It said 39 people who were in direct contact with the man had been quarantined.