Short answers, pulled from the story.
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. When bacteria, viruses, or fungi invade these spaces, they trigger an immune response that fills the alveoli with fluid, pus, and dead cells, creating a consolidation that prevents oxygen from entering the bloodstream.
Sir William Osler coined the moniker the old man's friend in 1918. This name reflected a dark reality of the pre-antibiotic era where death from pneumonia was often quick and painless compared to the slow, agonizing decline of tuberculosis or cancer.
More than 100 strains of infectious agents have been identified, with Streptococcus pneumoniae isolated in nearly 50 percent of community-acquired cases. Other causes include viruses like influenza and respiratory syncytial virus, fungi such as Histoplasma capsulatum, and parasites like Toxoplasma gondii.
In 2010, the disease resulted in 1.3 million deaths among children under five, with 95 percent of these occurring in the developing world. Rates occur about five times more frequently in the developing world than in the developed world, with countries like India, China, and Pakistan bearing the greatest burden.
In October 2024, the Centers for Disease Control and Prevention lowered the age for adult pneumococcal vaccination from 65 to 50 years old. This change gives more adults the opportunity to protect themselves from pneumococcal disease at the age when risk of infection substantially increases.