MENINGITIS

inflammation of the meninges, the membranes covering the brain and spinal cord. It can be caused by various infectious agents, including viruses, fungi, and protozoa, but bacteria produce the most life-threatening forms. Among the bacteria that can cause meningitis are the meningococcus (Neisseria meningitidis), the influenza bacillus (Haemophilus influenzae), and various strains of pneumococci, streptococci, or staphylococci. A bacterial infection elsewhere in the body may be carried to the meninges through the bloodstream itself or from an adjacent infected organ, such as the middle ear or the nasal sinuses. The infectious agents multiply in the meninges, where they produce a pus that thickens the cerebrospinal fluid, thereby causing various symptoms and complications. Bacterial meningitis usually has three main stages. At first, the bacteria multiply in the nasal passages and throat, often causing no painful symptoms. Next, they invade the blood, introducing toxic substances into the circulation and causing fever; if the infection is caused by N. meningitidis, a rash may appear and develop into hemorrhagic spots (petechiae) in severe cases. In the third stage, meningitis develops when the bacteria multiply in the meninges, where they produce intense inflammatory changes and an exudate of pus. A characteristic of meningitis is the rapid onset of symptoms, which may result in death within only a few hours. The first symptom of meningitis is usually vomiting. A severe bursting headache develops because the meninges have become inflamed and the pressure of the cerebrospinal fluid has increased. Stiffness of the neck then develops, due to irritation of the spinal nerves supplying those muscles. The degree of stiffness varies, but often the head is retracted, and in small children the head and spine may be drawn backward like a bow. Deep reflexes are exaggerated, and convulsions may occur in infants and small children. In more severe cases, the cerebrospinal fluid becomes so thickened by pus that the passages between the ventricles (cavities) of the brain and the spaces in the spinal meninges become blocked, causing fluid to accumulate. The accumulation of fluid in the ventricles may in turn result in internal hydrocephalus, which causes coma and death unless relieved. A diagnosis of bacterial meningitis is made with certainty by obtaining a sample of cerebrospinal fluid by lumbar puncture and examining it microscopically for the presence of bacteria and for increases in certain types of cells. The term meningitis most often refers to meningococcal meningitis, which is caused by N. meningitidis. Epidemics of this disease occurred at irregular intervals, with death occurring in 4050 percent of cases, until the use of antibiotic drugs greatly reduced both mortality rates and the incidence of the disease. Meningococcal meningitis is worldwide in distribution and more likely to occur in cold weather. It is primarily a disease of youth and especially of children under age 10, though all ages may be affected. The disease is usually acquired by nasal droplet transmission. Another serious cause of meningitis is Haemophilus influenzae; it occurs in infants and young children but only rarely in older persons, and its course and symptoms resemble those of N. meningitidis. The bacterium Streptococcus pneumoniae is a common cause of meningitis in adults. The early diagnosis and prompt treatment of meningitis is particularly important in preventing possible permanent damage to the brain, especially in affected children. Meningococcal meningitis is best treated with penicillin. Cases caused by H. influenzae are treated with ampicillin or chloramphenicol. These drugs have reduced mortality rates from bacterial meningitis to less than 5 percent in some areas. A vaccine that gives protection against the type b strain of H. influenzae became commercially available in the 1980s and has proved effective in safeguarding infants and children from the disease. Various other forms of meningitis are caused by viruses and ordinarily have a short, uncomplicated, self-limited course that does not require therapy.