pneumococcus

Pneumococcus is the single most common bacterium behind serious pneumonia, the germ doctors think of first when an otherwise healthy adult develops a sudden, severe lung infection. Many people carry it harmlessly in the nose and throat, but when it slips down into the lungs of a vulnerable person it can cause classic, hard-hitting pneumonia.

Its proper name is Streptococcus pneumoniae, a Gram-positive bacterium that grows in pairs and short chains and wears a sugar capsule that shields it from the immune system. That capsule comes in many varieties, called serotypes, which matters because vaccines are built to recognize the most dangerous of them. Beyond the lungs, pneumococcus also causes ear infections, sinusitis, bloodstream infection and meningitis.

Penicillin and related antibiotics have long been the mainstay of treatment, though resistance has grown in some regions, so local patterns guide drug choice. Two highly effective vaccines — a conjugate and a polysaccharide type — substantially reduce severe pneumococcal disease and are recommended for young children, older adults and people with chronic illness or weakened immunity.

Carrying pneumococcus in the throat is common and usually causes no illness; disease arises only when the balance tips — for instance after a viral infection like influenza damages the airway lining and lets the bacteria invade.