On June 8 former South African president and cultural icon Nelson Mandela, 94, was hospitalized for a recurring lung infection. As his health remains “critical but stable,” questions arise about the cause of Mandela’s infections, which began when he contracted tuberculosis during his time as a political prisoner. One factor may be extremely relevant: Mandela’s advanced age.

To help explain pulmonary infections and their frequency in the elderly, Scientific American sat down with Steven E. Weinberger, an internist and pulmonologist with the American College of Physicians in Philadelphia. Weinberger spent more than 25 years on the faculty of Harvard Medical School and has authored a textbook on pulmonary medicine.

[An edited transcript of the interview follows.]

What causes lung infections?

It depends a lot on the specific kind of infection. There are many kinds of lung infections, ranging from viral to bacterial—and tuberculosis, which is bacterial. What we’re talking about is the balance between what gets into the body and what the body’s defense systems can handle. We are all exposed to infectious agents all the time but we have an incredible defense system starting in the nose, mouth and throat. There are defense cells, things called macrophages, which will ingest bacteria and viruses. We also have an immune system that will develop antibodies. In essence, we have a multifactorial defense system.*

Why are these infections more common in older people?

Certainly the body’s defense mechanisms change with age. There’s something called immunosenescence: with age, some of the immune system cells are less capable of making antibodies.

What I’ve read about Nelson Mandela tells me his infection is recurrent. One wonders if there are any structural changes in his lungs. For example, if he has any form of underlying lung disease, that will affect the lung’s defenses and may make him more susceptible to infections. These kinds of structural changes are more common in older people.

What kind of symptoms are associated with lung infections?

The main symptoms will be cough, sputum production and fever. If it’s a chronic infection, it can debilitate the patient. It can cause weight loss, fatigue, malaise, etcetera. In some infections they may be spitting up blood as well.

What kinds of treatment options are available?

The treatment options are focused on the specific type of bacteria and the setting in which the infection developed. For the most common type of pneumonia infection, there are antibiotics that can be prescribed. If it’s something like tuberculosis, there’s a totally different set of antibiotics and a totally different duration of treatment. It requires a much more prolonged therapy.

How could someone avoid their vulnerability to lung infections as they age?

There are a couple of vaccinations that are important: the annual influenza and typically a single dose of the pneumococcal vaccine.* None of these are uniformly effective, but they are the main preventive options. Oral hygiene is also important. If oral hygiene is bad, there will be more bacteria in the mouth that will end up in the lungs, particularly while we’re sleeping. Avoid smoking: by virtue of causing underlying lung diseases, it can predispose people to infections.

*Editor's Note (6/28/13): For purposes of clarification, these sentences were edited after posting.