Pope Francis is battling a complex respiratory infection and will remain in hospital as long as necessary, the Vatican has said.
The 88-year-old pontiff has been sick for over a week and was admitted to Rome's Gemelli Hospital on Friday.
In a brief statement on Monday, a Vatican spokesperson said the pope's treatment plan had been changed.
"The results of the tests carried out in recent days and today have demonstrated a polymicrobial infection of the respiratory tract, which has led to a further modification of the therapy," the spokesperson said.
A polymicrobial infection is one caused by two or more micro-organisms, and can be caused by bacteria, viruses, or fungi.
While a bacterial infection can be treated with antibiotics, viral infections cannot. Viruses usually have to run their course, but the patient can be assisted with other medicines to bring down their fever or help their body fight the infection.
"All tests conducted up to today are indicative of a complex clinical picture that will require an appropriate hospital stay," the Vatican added.
Earlier, Vatican spokesperson Matteo Brunit said Pope Francis was in "good spirits".
Papal events cancelled
Pilgrims visiting the Vatican on Monday were hopeful that Pope Francis would recover soon.
"We certainly wish for him to get better very quickly," said Rev. Tyler Carter, a Catholic priest from the United States.
"He is our father and our shepherd, and so we want his continued health and blessing."
Italian tourist Manuel Rossi said he was "quite worried" when the pope cancelled a planned appearance on Sunday.
"I am 18 years old so I have seen few popes in my life, and am very close to him," Mr Rossi said.
"I hope he recovers as soon as possible."
The Vatican said on Monday that the pope's planned weekly audience in St Peter's Square, set for Wednesday, had been cancelled "due to the continued hospitalisation of the Holy Father".
The pope's doctors had earlier ordered complete rest, and Pope Francis was unable to deliver his regular weekly prayer on Sunday to pilgrims in St Peter's Square or lead a special Mass for artists to mark the Catholic Church's Jubilee Year.
The pope has suffered a number of medical setbacks in recent months, including a fall last month at his Santa Marta residence where he hurt his right arm.
A separate fall in December led to a visible bruise on his chin. He had collided with a night stand.
ABC/Reuters
