ROME >> Pope Francis’ respiratory infection is presenting a “complex clinical picture” that will require further hospitalization, the Vatican said Monday, as concerns grew about the increasingly frail health of the 88-year-old pontiff.

Vatican spokesman Matteo Bruni said the results of tests conducted in recent days and Monday indicate the pope is suffering from a polymicrobial respiratory tract infection that has necessitated a second change in his drug therapy since being hospitalized Friday. Scientists say polymicrobial diseases are caused by a mix of viruses, bacteria, fungi and parasites.

There was no timeframe given for his hospitalization, which at Day 4 has already sidelined Francis for longer than a 2023 hospitalization for pneumonia. Bruni said the complexity of his symptoms “will require an appropriate hospital stay.”

In a late update Monday, Bruni said Francis’ condition was “stationary,” and that he had resumed some work activities and reading.

Francis had part of one lung removed after a pulmonary infection as a young man and is prone to bouts of bronchitis in winter. He was admitted to Rome’s Gemelli hospital in a “fair” condition on Friday after a weeklong bout of bronchitis worsened. Doctors confirmed a respiratory tract infection and prescribed “absolute rest” alongside unspecified drug therapies. Subsequent updates said his slight fever had gone away and that he was in “stationary” condition.