Pope Francis will remain in a Rome hospital after being admitted late last week following a series of tests that indicated a “complex clinical picture,” the Vatican said on Monday, raising fresh concerns about the 88-year-old pontiff’s health.

Diagnostic tests carried out after Francis was taken to Policlinico A. Gemelli on Friday presented “a polymicrobial respiratory tract infection,” and his doctors had changed treatment accordingly, the Vatican said in a statement.

The complex clinical picture “would require an appropriate medical stay,” it said, without elaborating.

Francis was hospitalized in 2023 with a respiratory infection, but was able to leave the hospital after three days.

Francis has had a busy schedule since New Year’s Eve, when he presided over the opening of the 2025 Jubilee, held every 25 years in the Roman Catholic Church.

The Vatican announced in early February that Francis had bronchitis, but he continued his activities, holding smaller audiences at the Casa Santa Marta, the Vatican guesthouse where he lives, but presiding over larger gatherings and Masses with thousands of pilgrims, including an outdoor Mass in St. Peter’s Square earlier this month.

The Vatican said that a general audience on Wednesday was canceled.

After he entered the hospital, doctors prescribed complete rest. Subsequent medical updates said he was in “stable” condition.

The pope, who had part of a lung removed as a young man, has a recent history of medical challenges. He has knee problems and sciatica that have caused a severe limp and, in recent years, often required him to use a wheelchair, walker or cane.

In 2021, he had colon surgery. After his bout with bronchitis in 2023, he was hospitalized again a few months later to undergo abdominal surgery for a hernia. Last year, he underwent diagnostic tests at the Gemelli hospital after a slight flu.

On Monday morning, Francis ate breakfast and read some newspapers after a restful night, said Matteo Bruni, a Vatican spokesman, adding that the pontiff was “in good spirits.” Mr. Bruni said a medical update would be issued later Monday.