Pneumonia

Pneumonia is an infection of the lung tissue in which the alveoli, the tiny air sacs where oxygen passes into the blood, become inflamed and fill with fluid, pus and white blood cells. Bacteria cause most cases, and Streptococcus pneumoniae is the leading cause of pneumonia caught outside hospitals. Viruses such as influenza, RSV and SARS-CoV-2, and less often fungi, are other causes, and breathing food, drink or vomit into the airways can set off aspiration pneumonia.

As the air sacs flood, a change doctors call consolidation, less oxygen reaches the blood. Typical signs are a cough that may bring up mucus, fever, chills, fast or labored breathing and chest pain that worsens on breathing in. The risk is highest in babies, adults over 65, smokers and people with weak immunity or long-term illness, and older patients may show little more than confusion or weakness. Bacteria can spread into the bloodstream and cause sepsis, and fluid or pus can collect around the lung.

Diagnosis rests on the history, crackling sounds heard through a stethoscope and a chest X-ray showing white patches; sputum and blood tests can name the microbe. Bacterial pneumonia is treated with antibiotics, viral cases mostly with supportive care, and severe illness with oxygen in the hospital. Pneumococcal and flu vaccines lower the risk.