Streptococcus pneumoniae, or pneumococcus, is a bacteria that causes many different kinds of infections in people, ranging from ear infections and sinus infections to pneumonia, meningitis, and sepsis.
Although the names (and bacterial genuses) are similar, S. pneumoniae is quite different from group A streptococcus (the bacteria that causes strep throat and rheumatic fever). S. pneumoniae infections are on the average much more serious -- pneumococcus is the most common cause of bacterial meningitis in the United States, and about 8% of children with pneumococcal meningitis die of the infection, while 1 out of 4 surviving children, or more, have neurologic damage including hearing loss after "getting over" the infection. And it's a pretty common bug to be infected with: pneumococci are the most common cause of ear infections and sinus infections, as well as the most common bacteria found in the blood of children under 2 years old with fevers, many of whom have no obvious site of infection.
Many people have pneumococci in their noses and throats but have no symptoms. The bacteria is transmitted from one person to another, usually by droplets. Like viral upper respiratory infections, pneumococcal infections are more common in winter. Infection can begin as little as 1-3 days after exposure. Studies of ear fluid cultures suggest that anywhere from 20 to 40% of ear infections are caused by pneumococcus. The signs of pneumococcal meningitis and sepsis can be the same as those of meningococcal meningitis. Often, however, pneumococcal infection can appear first as a high fever with a very high white-blood-cell count (where almost all of the white cells are neutrophils or bacteria-fighting cells) and no obvious site of infection.
There are also some people who are more susceptible to pneumococcal infections than others. One particular group of people who are more likely to be infected are those whose spleens have been damaged or removed -- whether because of injury or because of disease. People with sickle-cell anemia are at special risk, because repeated sickle-cell crises and the resulting damage to red blood cells results in destruction of spleen tissue. Most doctors assume that if you have sickle-cell disease, your spleen will not be working any more by, at the latest, your 20's -- and so we vaccinate sickle-cell patients against bacteria, such as pneumococcus and meningococcus, which healthy people's spleens help their bodies kill. Unfortunately the vaccines aren't perfect, and there are many bacteria that sicklers are prone to be infected with that we don't have vaccines for. Other people who are more susceptible to pneumococcus than the average person are those with immune system problems (including AIDS, but also people who do not produce enough of certain kinds of white cells or who lack other important components of their immune systems, or those with some kinds of chronic illness that weaken their immune systems).
Once upon a time, long, long ago, pneumococcal infections could be treated with penicillin G, but penicillin-G-resistant pneumococci have become more and more common, especially with antibiotic overuse (this is one reason why we use so many different antibiotics to treat ear infections). We usually start meningitis or sepsis treatment with third-generation cephalosporins such as ceftriaxone, until the cultures have been completed and we know what antibiotics can be used. Even ceftriaxone may not work, though: in some communities almost half of the pneumococcus samples isolated from patients' culture are resistant to ceftriaxone.
There are over 80 different known strains or "serotypes" of pneumococcus. Some are more prevalent in different areas; some are more prevalent in children, while others are more common in adults. We have had a vaccine available for many years -- Pneumovax® -- that gives at least some immunity against 23 different serotypes of pneumococcus. It's not a perfect vaccine -- for one thing, the immunity it induces doesn't last for a lifetime, and it doesn't induce immunity well in children younger than age 2 years -- but it can give you some protection if you are otherwise susceptible (for example, we routinely give it to people with sickle-cell disease, or who have lost their spleens after injuries).
Prevnar® is a different kind of pneumococcal vaccine, approved in early 2000. In its original form ("Prevnar 7") Prevnar protected against only 7 different serotypes of pneumococcus. On February 24, 2010, the US Food and Drug Administration approved a new version -- "Prevnar 13" -- that protects against 13 serotypes, including one serotype (serotype 19-A) that is resistant to many antibiotics. Unlike Pneumovax, Prevnar induces immunity even if given as early as age 2 months. The Centers for Diease Control and Prevention and other infectious-disease and public- and children's-health authorities recommend this new vaccine starting in infancy. The recommended schedule for Prevnar is at ages 2, 4, 6, and 15 months if the series is started in infancy (this is similar to the schedule for the diphtheria - pertussis - tetanus (DTaP) and Hib vaccines); the vaccine is also being recommended for older children, up to school age, although the number of doses will be less depending on how old your child is. As always, ask your doctor for more information on the vaccine and its benefits and possible side effects for your child.