Clinical Manifestations and Pathology

Infection with N. meningitidis can result in one of three conditions. In the large majority of cases, bacteria are carried in the nose and pharynx without any symptoms or with just a sore throat. Serious disease develops only if the bacteria reach the bloodstream. This can produce fulminating blood infection or meningococcemia, which is characterized by sudden prostration, high fever, skin blotches (ecchymoses), and collapse. Most of these cases are fatal unless promptly treated, and death may ensue in a matter of hours, before the meninges become involved.

Meningitis, however, is the more common result, occurring when bacteria travel through the blood to infect the membranes of the brain and spinal cord. Fever, violent headache, stiff neck, and vomiting are typical symptoms, and, as in meningococcemia, many victims show a petechial rash due to blockage of small blood vessels. A thick, purulent exudate covers the brain, and arthritis, cardiac damage, and shock may develop. Coma, convulsions, and delirium are frequent, and death rates for untreated cases range from 50 to 90 percent. Even in epidemic conditions, however, only a small minority of persons harboring the organism develop clinical disease. It is not known why most people remain healthy carriers whereas others become desperately ill. Individual susceptibility, damage to mucous membranes, and concomitant infections with other bacteria may all play a role.

Diagnosis is based on clinical signs and the recovery of pathogens from the cerebrospinal fluid or, in meningococcemia, from the blood. Culture of organisms from throat swabs is used to monitor carrier rates and circulating strains.

Therapy was revolutionized with the introduction of sulfa drugs in the late 1930s, and sulfonamides were widely used as a prophylaxis for exposed populations. The appearance and spread of sulfonamide-resistant bacteria after 1963 has forced a shift in preventive tactics, but the pathogen is still very sensitive to treatment with penicillin. Military re cruits are routinely vaccinated in most countries, and extensive inoculation campaigns have helped control epidemics in Africa. Better ventilation and reductions in crowding in living and sleeping areas are useful in barracks and other institutional settings. Prophylaxis with rifampin is helpful in reducing carrier rates and preventing outbreaks after cases have occurred in specific populations, as, for example, children in day-care centers.

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