An Italian employee of the Holy See who lives in the same residence as Pope Francis was reported on Thursday to have tested positive for COVID-19 and has been hospitalised.
Several Italian newspapers with reputable sources in the Vatican said the clergyman has lived for years in the Saint Martha's guesthouse.
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 hospitalised in Rome and that his office has been disinfected.
Pope Francis has remained largely secluded at his residence since coming down with a cold late last month. The 83-year-old pontiff has a small apartment in the building and takes his meals there.
He also has private meetings and occasionally moves to the Vatican library to record livestreamed messages to the world's 1.3 billion Catholics. La Stampa said Pope Francis has been "eating alone in his room for some time" as a precaution.
"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," La Stampa wrote, adding that secretaries bring his meals to him on a tray.
Vatican spokesman Matteo Bruni told AFP he could neither confirm nor deny the reports.
The official Vatican News site said the number of people infected in the city state has risen to four.
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 traditionally 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.
Cardinals stay there during conclaves held to elect new popes, when the building becomes filled with intrigue.
Il Messaggero said that currently only about 30 people live at the residence and that "no one would have expected" that 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 four 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.
