How Pneumococci are Spread Pneumococci are spread from person-to-person by coughing, sneezing, or close contact. When a person is first exposed the pneumococci stick to the surface of cells lining the respiratory tract. A balance then develops between the body’s ability to eliminate the organisms, and the rate at which the organisms multiply. This is referred to as colonization. Persons who are colonized do not realize it, that is, they have no symptoms. Over time colonization causes an immune response and antibodies develop against the pneumococcal serotype causing the colonization. Once this so-called type-specific immunity develops, the body can successfully eliminate these organisms from the respiratory tract. The process of colonization, immunity, and elimination occurs repeatedly with different pneumococcal serotypes, particularly in infants and young children. Over time, the body develops antibodies against a variety of pneumococcal serotypes. How Infection Occurs Persons are at greatest risk of developing pneumococcal disease during the early phases of colonization before the immune system has produced specific antibodies against the colonizing pneumococcal serotype. It is at that time that pneumococci can spread to the middle ear or lung, causing infection. Once a local infection develops, pneumococci can multiply and invade the blood stream, resulting in a very serious condition known as bacteremia or blood stream infection. Pneumococci which have invaded the blood stream can then spread to other locations in the body, such as the coverings of the brain and spinal cord. Middle Ear Infections Infants and young children are very susceptible to middle ear infections (acute otitis media). Acute otitis media may be caused by the pneumococcus, other bacteria, or viruses. Pneumococci are the most common bacteria causing acute otitis media. The highest rate of infection occurs at 6 to 18 month of age, and almost all children suffer one or more episodes of acute otitis media by 3 years of age. Symptoms of acute otitis media may include some or all of the following: irritability, crying, ear pain, ear drainage, fever, feeding problems, vomiting, and hearing impairment. Pediatricians diagnose acute otitis media by the patients’ history, by the patients’ signs and symptoms, and by examination of the eardrum with a device called an otoscope. The view of the eardrum that the physician might see in acute otitis media, compared to a normal eardrum, is shown in Figure 5. Infants are very susceptible to pneumococcal acute otitis media because they are born with very small amounts of pneumococcal antibodies which have been passed to them from their mothers. These antibodies further decrease over the first 3 to 6 months after birth. Infants are then susceptible to colonization and infection from any one of the several pneumococcal serotypes which may be circulating in their community. In addition, the tube connecting the middle ear to the throat, called the eustachian tube, is shorter, wider, and more horizontal early in life which allows for easier spread of bacteria from the throat to the middle ear. The result is a series of painful episodes of acute otitis media which decrease over time as the middle ear matures, the eustachian tube becomes less horizontal, and as the infant develops antibodies against many of the pneumococcal serotypes. Pneumonia Pneumonia is a serious lung infection. Some common symptoms of pneumonia are fever, chills, cough, shortness of breath, chest pain and increased sputum production. Pneumonia may be caused by viruses, bacteria or fungi. However, the pneumococcus is the most important cause of serious pneumonia. Dr. William Osler, perhaps the most influential physician in the 20th century, described acute pneumonia as the "captain of the men of death" in the first modern textbook of medicine (Figure 6). Dr. Osler described pneumonia this way because in the early 1900s it was common and when it occurred in older persons it was almost always fatal. This situation changed dramatically in the late 1930s when sulfonamides, the first of a long list of antibiotics which could successfully treat pneumococcal pneumonia, were introduced. By 1945 penicillin had been shown to be a highly effective treatment for pneumococcal pneumonia. For the next 40 years the treatment of pneumococcal pneumonia with antibiotics was cheap and effective. Mankind has benefitted greatly from the introduction of these powerful antibiotics. However, the continued use and misuse of antibiotics has led to the gradual development of resistance of pneumococci to penicillin and other commonly used antibiotics. This development has led to a new appreciation for sound preventive strategies such as proper use of influenza and pneumococcal vaccines. Over 90 percent of serious pneumococcal disease in adults occurs as pneumonia. Because the most important defense against the pneumococcus is the presence of type-specific antibody, medical conditions which depress the body’s immune response place persons at higher risk of invasive pneumococcal disease. Common conditions associated with depressed immune response include HIV infection, cancer, and treatment with certain drugs like corticosteroids (steroids). Also, since the activity of the immune system decreases with age, pneumococcal pneumonia is more common with advanced age. The diagnosis of pneumonia is usually straightforward. Patients initially may be ill with a viral upper respiratory tract infection. A few days into the illness the patient suddenly becomes much sicker with fever, chest pain, shortness of breath, shaking chills and increased sputum production. The sputum may change color and can be rust-colored. Patients often can precisely date "when things got worse" and when that happens they either call their physician or go to an emergency room for help. The diagnosis of pneumonia is made by physical examination findings, chest X-rays, and other laboratory tests such as a white blood cell count. During pneumonia, the chest X-ray will show a shadow (infiltrate) in the area where the infection and inflammation is occurring (Figure 7). Because several different kinds of bacteria can cause pneumonia, physicians often order sputum stains and sputum and blood cultures. In about one-half of cases of pneumococcal pneumonia, sputum stains have a characteristic picture that is strongly suggestive of pneumococcal infection. An example of such a stain is shown in Figure 3. Such information is very helpful to the physician because it can be made available within minutes. Sputum samples are also placed onto special gels in small dishes called petri dishes or plates. The plates are placed in warmers called incubators at a temperature of 37oC (98.6oF). Twenty four hours later the plates are examined for the presence of pneumococci or other organisms capable of causing pneumonia. However, it is important to note that, at best, current laboratory testing is only able to identify the cause of pneumonia in about one half of cases. Nonetheless, most studies of pneumonia show that the most common cause of serious pneumonia is the pneumococcus. Blood Stream Infection In about 20 percent of cases of pneumococcal pneumonia, the pneumococcus will spill over from lung tissue and invade the blood stream. Blood stream infection, also referred to as bacteremia, commonly causes shaking chills and fever. In serious cases the pulse rate may become rapid and the blood pressure may become dangerously low. All cases of blood stream infection, regardless of the type of bacteria causing them, need to be quickly diagnosed and treated. Bacteremias are confirmed by doing cultures of blood. Since blood is normally sterile, the growth of bacteria from a blood sample is always taken seriously. Once in the blood stream, organisms may spread to other parts of the body, such as joints (septic arthritis), coverings of the brain and spinal cord (meningitis), and heart valves (endocarditis). These complications dramatically increase the seriousness of the illness and the risk of death from these infections. Pneumococcal Infections in Very High Risk Populations While a number of groups are at high risk for pneumococcal infections and/or complications of pneumococcal disease (see section entitled "Who should receive pneumococcal vaccine") there are two very high risk populations that bear special mention: persons with human immunodeficiency virus (HIV) infection and persons who do not have a spleen. HIV infected persons suffer some of the highest rates of pneumococcal infection, currently estimated to be in the range of about 2 percent per year. Persons with no spleens are also at high risk from invasive disease. The spleen is an important organ in the early production of antibody against pneumococci as well as a site for removal of bacteria that spill into the blood. Surgical removal of the spleen, called a splenectomy, and medical conditions affecting the spleen (for example sickle cell disease) significantly increase the risk from invasive pneumococcal disease. Vaccination of these and other high risk groups such as persons 65 years of age and older is a high priority. Treatment of Pneumococcal Infections Antibiotics are the most important therapy for treatment of pneumococcal infections. Use of antibiotics has resulted in a 90 percent decrease in mortality rates among patients with pneumococcal infections, particularly in patients with invasive disease. Until recently pneumococci were very sensitive to penicillin and penicillin-like antibiotics. However, in recent years pneumococci have become progressively more resistant to penicillin, a trend which has continued (Figure 8). This increased resistance to penicillin is causing problems for physicians. What was once a relatively simple, cheap, and effective treatment for invasive pneumococcal disease (that is, penicillin) has become more complicated and much more expensive. For the most part, when these infections occur they can be managed with currently available antibiotics. However, this is a changing situation because of evolving drug resistance which must be continuously monitored. As result, physicians and public health officials have become more interested in measures to prevent pneumococci from causing infection. Such measures rely on the increased use of existing pneumococcal vaccine and the development of newer, more effective vaccines.