What does Pope Francis having "double pneumonia" mean? What should you look for in the elderly? How can you avoid getting pneumonia?

Pope Francis is being treated in hospital for double pneumonia — but what is this condition, and why might the pope be particularly vulnerable to it?

The condition, which entails pneumonia in both lungs, is potentially grave, according to health experts. Pope Francis, who remains hospitalized, has bilateral pneumonia, the Vatican said on Tuesday.