(NEW YORK) -- Newly elected Pope Francis is two years younger than Pope Benedict XVI was when he was elected in 2005, but the 76-year-old from Argentina still has at least one health issue: He has only one lung.

Pope Francis, formerly known as Cardinal Jorge Bergoglio, had one of his lungs removed when he was a teenager because of an infection.

“Obviously, this was a success because here he is at age 76,” said Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn. “So whatever they did got him over that precarious period.”

Schaffner, a former president of the National Foundation for Infectious Diseases, said there are several reasons the new pope could have had his lung removed about six decades ago:

1.) Pope Francis could have had tuberculosis.

“Back when he was a young person, there was not yet widespread antibiotic drug therapy, and it is possible that he had substantial involvement of a lung or part of a lung and had to have it removed,” Schaffner said. “That was a pretty standard treatment in the pre-antibiotic drug era.”

2.) He could have had a complication of whooping cough, or pertussis.

“Whooping cough can cause disease of the bronchial tube and can cause chronic infection,” Schaffner said.

3.) He could have had pneumonia and developed complications.

“Once again, this was before conventional antibiotics were widely available, and so they may have had to treat this complication with surgery by taking out all or part of his lung,” Schaffner said.

4.) Finally, he could have been born with a congenital lung defect that got infected.

“They could not eradicate the infection and, once again, did not have all the antibiotic supportive care that we have today,” Schaffner said. “They just cut out infection.”

Although these infections would have been more common in a middle-aged person than a teenager, Schaffner said they’re the most likely possibilities given the limited information about the lung removal.

Asked whether a person can survive with one lung, Schaffner said, “Easily” -- lungs are redundant, so people who have one removed are able to live normal lives.

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