Several Italian newspapers with reputable sources in the Vatican said the Italian clergyman who got sick had lived for years in the pope's Saint Martha's residence.
Il Messaggero said the person is "one of the pope's closest collaborators, an official of the Secretariate of the State, who was found to have a slight temperature after going in for a routine check."
The daily La Stampa said the unnamed person has been hospitalized in Rome and that his office has been disinfected.
Il Messaggero later reported that the pope himself was tested for the virus and came out clean.
The 83-year-old pontiff has remained largely secluded at his residence since coming down with a cold late February.
La Stampa said he has been "eating alone in his room for some time" and has food brought to him on a tray by secretaries.
"He spends much of his time in his apartment, and when he moves inside the residence, he keeps the necessary safe distances," La Stampa wrote.
"The anti-contagion cordon has been tight around the pope for weeks."
The official Vatican News site said the number of people infected in the city state has risen to 4.
The ANSA news agency said the Italian clergyman in the pope's residence was a fifth case not reported by official sources.
Life in the Vatican has been shrouded in secrecy and little in known about how popes spend their days.
But the Argentine-born pontiff has tried to connect more with the people and do away with some the Vatican's more formal traditions.
He refused to move into the luxurious papal palace upon being elected to succeed pope Benedict XVI in March 2013.
His Saint Martha's residence is a simple building erected next to Saint Peter's Basilica in 1996.
It is also the place where cardinals stay when they gather for conclaves to elect new popes.
Francis stayed there for the 2013 election and then never moved out when he was picked.
Il Messaggero said only about 30 people live at the residence and "no one would have expected" for one of them would get sick because their circle of contacts was so small.
The Argentine-born pontiff has enjoyed a life of good health despite losing part of a lung as a young man and suffering from sciatica – a nerve condition that causes pain in his hip.
Italian news reports said he was not currently considering moving to a more isolated location because of the 4 cases in the Vatican.
"In any case, the pope is constantly surrounded by a staff equipped with disinfectant products," La Stampa wrote.
The pope's daily prayer Thursday touched on people's fears in the face of the new disease.
"Each one knows what their own fears are," Francis said. – Rappler.com