How Meningococcal Organisms are Spread When a person is exposed to meningococcus from a colonized or an infected person’s secretions, through coughing, sneezing or close contact, one of two events may occur. The first event to occur is that the meningococcal organisms adhere or stick to the surface of the cells lining the upper respiratory tract including the throat and nose. The body’s defense mechanisms usually are able to keep the organisms from spreading to other parts of the body. This localization results in colonization of the nose and throat and is referred to as the carrier state. Persons who are colonized do not realize it since they have no signs or symptoms of disease. Physical damage to the lining of the nose and throat by active or passive cigarette smoke or by a preceding viral infection may enhance colonization. Colonization by meningococci may persist for several weeks to months. The carriage rate is less than 3% in children 4 years of age and under, increases to a maximum of 25 to 35% at 15 to 24 years of age and decreases to less than 10% in older age groups. Higher carrier rates have been reported in persons in confined or linked populations such as military recruits, pilgrims, boarding school students and prisoners. The rate of carriage is higher in persons in lower socioeconomic groups, probably because of crowding. Meningococci do not survive well outside their human host and have no alternate host. The lining of a person’s nose and throat is the only natural reservoir of N. meningitidis. Therefore transmission or spread of these organisms occurs from one person to another person and not from other animals. The second event that may occur following exposure to meningococci is disease. In most instances the body is able to localize the meningococcal organisms, but occasionally organisms spread from the throat to other parts of the body and result in disease. How Meningococcal Disease Occurs Following exposure and colonization, meningococci may pass through the lining of the nose or throat and into the bloodstream (meningococcemia). Once in the bloodstream, organisms may spread to the coverings of the brain and spinal cord (meningitis) and less frequently to other parts of the body. Persons are at greatest risk of developing disease during the early phase of colonization before the body’s immune system has produced specific antibodies against the colonizing meningococcal strain. It is at this time that the organisms can spread to the blood and brain. In addition, some people have defects in a part of their immune systems, called the complement system, that predispose them to infection with meningococci. Types of Disease and Signs and Symptoms Disease caused by the meningococcus usually results in meningococcemia, meningitis, or both. Meningococcemia is usually characterized by acute fever, chills, malaise, low back and thigh pain, generalized muscle aches, and a rash that occurs in about 75% of patients. The rash may be mild (figure 7a) or severe (figure 7b). In overwhelming infections, problems with blood clotting occur, resulting in shock (dangerously low blood pressure) and death. Meningococci also cause meningitis, which is difficult to distinguish from meningitis caused by other bacteria such as Streptococcus pneumoniae. Based on the sequence of events, patients with meningococcal disease can be classified into one of the following groups.

		meningococcemia without shock and without meningitis
		meningococcemia with shock but without meningitis
		meningitis and shock
		meningitis but without shock

Meningococci also cause arthritis, which is a relatively frequent complication of meningococcemia, and pericarditis (involvement of the covering of the heart). Rare manifestations of infection include conjunctivitis (infection of the coverings of the eye similar to ‘pink-eye’), endophthalmitis (infection of the inside of the eyeball), sinusitis, and pneumonia. Will You Get Well If Infected? Disease caused by N. meningitidis is serious. Despite therapy with antimicrobial agents such as penicillin, to which strains in the United States remain susceptible, the case-fatality ratio is between 10% and 15%. The case fatality ratio is the number of deaths divided by the number of cases of disease and is often expressed as a percentage. How The Diagnosis Is Made Case definitions for invasive meningococcal disease are given in table 1. These definitions are useful to public health officials and epidemiologists who keep track of meningococcal cases. Cultures of blood and cerebral spinal fluid are obtained in all patients with suspected invasive meningococcal disease. Cultures of involved skin, joint fluid and sputum (coughed up phlegm) are positive in some patients. Since N. meningitidis can colonize the nose and throat without causing disease, detection of N. meningitidis from these sites is not helpful in making decisions about treatment. How Meningococcal Disease Is Treated Antibiotics are the most important therapy for treatment of meningococcal infections. Use of antibiotics has resulted in a significant decrease in mortality rates among patients with invasive meningococcal disease. Luckily, meningococci in the United States have remained susceptible to penicillin, which is the drug of choice used to treat persons with invasive meningococcal infections. However, penicillin-resistant strains have been reported in other parts of the world.