Meningococcal Meningitis

Organism Neisseria meningitidis. Many ser-ogroups and sub-groups have been identified, but of these A, B, C and Y are the most important in producing disease, while A and C predominate in epidemics. W135 has recently been responsible for some outbreaks.

Clinical features Fever, headache, vomiting, neck stiffness and progressive loss of consciousness. A petechial rash, which does not blanch, is an important sign. Infants show floppiness and high-pitched crying, while children may present with convulsions.

Diagnosis is by lumbar puncture, but should not delay early treatment, which can be given straight away and lumbar puncture done afterwards if necessary. A Gram stain is only reliable in some 50% of cases, so culture should be attempted wherever possible and sensitivity obtained. Blood should also be taken for culture and polymerase chain reaction (PCR). Smears from petechiae can also be examined by Gram stain.

Transmission is by airborne spread of droplets and from direct contact with secretions from the nose or throat. The organism is found commonly in the nasopharynx so other factors must also be responsible for meningitis to occur.

Epidemic meningitis was first studied in cooler climates and an association found with overcrowding, especially in military institutions. The organism when introduced into an overcrowded environment produced both cases and carriers (nasal). As the number of carriers increased, the number of cases of meningitis did so likewise.

However, in the African (Sahel) epidemic form, the heat makes people spend much of their time out of doors and overcrowding is not a phenomenon at this time of year (Fig. 13.4). Although overcrowding seems to increase the number of carriers and the potential for more cases, it does not explain the mechanism for causing meningitis.

The organism inhabits the nasal mucosa within which it is anatomically very close to the meninges, although separated by formidable barriers of bone and membrane. The generally accepted theory is that the organism passes from this site into the blood stream, crosses the blood-brain barrier and enters the cerebrospinal fluid (CSF). Experimental evidence does not substantiate this route unless there has been some trauma to the meninges. Difficult though the direct route may seem, it has been shown that minute passages through the bone of the skull do occur and transmission of organisms along this route is a possibility. Furthermore, if organisms are introduced directly into the sub-arachnoid space, infection will only occur if a critical level is exceeded (103 organisms in dogs), suggesting that this route could frequently be invaded, but only when there is excessive infection does meningitis develop. An alter native explanation is that transmission is directly from the nose through the skull and any traumatic insult to the nasal mucosa, such as the intense drying out during the Sahel hot season, or upper respiratory tract infection in colder climates, potentiates a greater number of organisms to pass along these minute channels and overcome the defences of the meninges.

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