(CNN) — Pope Francis has a “polymicrobial infection” of his respiratory tract that will require his hospital treatment to be changed, the Vatican said Monday, with tests indicating a “complex clinical picture” for one of the oldest popes in the church’s history.

The test results implied a further change in treatment requiring “adequate hospitalization” for the 88-year-old pontiff – who has long been plagued by a string of lung-related medical struggles.

“The results of the tests carried out in recent days and today have demonstrated a polymicrobial infection of the respiratory tract that has led to a further change in therapy,” the Vatican said in a statement.

“All the tests carried out to date are indicative of a complex clinical picture that will require adequate hospitalization.”

Later on Monday, the Vatican confirmed the pope remained in a stable clinical condition – without fever – and is continuing his prescribed therapy.

“This morning, he received the Eucharist and subsequently dedicated himself to some work activities and reading texts,” a statement from the Vatican said.

The statement added that the pope was “touched” by the messages of affection he continues to receive. “In particular he intends to express his thanks to those who are currently hospitalized, for the affection and love that they express through the drawings and good wishes,” it said.

“He prays for them and asks that they pray for him,” it added.

Polymicrobial infections are acute and chronic diseases that can be caused by a combination of viruses, bacteria, fungi and parasites, according to the US National Insititutes of Health.

Worshipers outside the Vatican expressed concern over the pope’s diagnosis and wished him a steady recovery. “We certainly wish for him to get better very quickly,” Rev. Tyler Carter, a US priest, told Reuters. “He is our father and our shepherd, and so we want his continued health and blessing.”

Manuel Rossi, a visitor from Milan, northern Italy, said: “I am 18 years old so I have seen few popes in my life, and am very close to him.

“I hope he recovers as soon as possible,” added Rossi.

‘He is more tired’

Earlier Monday, Francis slept well, read some newspapers and ate breakfast, according to Vatican spokesperson, Matteo Bruni, after he tried to complete routine obligations on the first two days of hospitalization.

On Friday and Saturday, the pope spoke on the phone to Rev. Gabriel Romanelli and his assistant, Father Yusuf Asad, in Gaza City, northern Gaza – who have been in frequent communication since Israel launched its war following the October 7 attacks.

After more than 15 months of “massacres, violence, fear, and hunger” in the Palestinian enclave, the pontiff called his colleagues “to check in,” Vatican News reported on Monday.

“We heard his voice. It is true, he is more tired,” reflected Romanelli. “He himself said, ‘I have to take care of myself.’ But you could hear the clear voice, he listened to us well.”

The pope was checked into a hospital in Rome last week for “diagnostic tests” relating to a respiratory tract infection, the Vatican added. They later confirmed he was in Agostino Gemelli Polyclinic in the Italian capital – and had canceled his meetings for the next three days, including his general audience scheduled Wednesday.

He did not lead the weekly Angelus prayer on Sunday – only the second time that this has happened in his almost 12-year-long papacy.

Doctors had prescribed “complete rest” for the pope, who had engaged in an intense round of meetings and public events until his hospitalization.

When he was younger, the Argentinian leader endured severe pneumonia and had part of one lung removed. More recently, he suffered two falls in recent months and has been seen using a wheelchair to help alleviate his restricted mobility.

Francis also has diverticulitis, a common condition that can cause the inflammation or infection of the colon. In 2021, he had surgery to remove part of his colon.

“We hope that the recovery will happen soon, and that he can return to St. Peter’s to continue his mission and work,” added Romanelli, the priest in Gaza City.