Meningococcal disease refers to disease caused by an organism called Neisseria meningitidis (abbreviation N meningitidis). Also known as meningococcus, this organism is a bacterium, not a virus. It can cause meningococcal meningitis, but it can also cause a blood infection, known as meningococcal septicaemia which is still fatal in a fifth. Rarer is either isolated meningococcal pneumonia or meningococcal bacteraemia which like isolated meningitis with appropriate antimicrobial therapy have a much better prognosis.
Meningococcal disease is uncommon, affecting approximately 1 person in every 20,000 each year. But it can be very serious. Meningococcal disease is the commonest infectious cause of death in children and young people up to 20 years, and it is the number one killer of children aged 1-5 years.
Presentation of meningococcal disease
There are three common forms of meningococcal disease:
- Meningitis alone
- Septicaemia (blood poisoning) alone where the organism is reproducing in the blood
- A combination of meningitis and septicaemia
These presentations tend to be associated with a classic pupuric rash but do not have to. The purpuric rash is present in 80%, classically being purpura fulminans in meningococcal septicaemia. Perhaps strangely given its reputation, meningococcal meningitis is a relatively benign form of bacterial meningitis, with lower rates of mortality and morbidity. Meningococcal septicaemia on the other hand can be catastrophic. Meningism can be present in meningococcal septicaemia, and also tends to predict a milder course (see Glasgow Meningococcal Sepsis Prognostic Score). Isolated meningococcal pneumonia is usually clinically indistinguishable to other community-acquired pneumonias until the blood culture comes back showing meningococcal bacteraemia.
Meningococcal septicaemia (meningococcaemia, meningococcemia) is a form of meningococcal disease associated with hyperinvasive serotypes of Neisseria meningitidis and associated even with appropriate antibiotic treatment with mortality rates of about 20%. The serotypes are A, B, C, Y and W-135 and are associated with dysfunction of endothelial protein C activation. Death due to fulminant meningococcal septicaemia may occur within hours of the first symptoms. While characteristic rashes (purpura fulminans) due to occlusion of small vessels by antigen antibody interaction in the dermis of skin are found in more than 80% cases it may be absent during early phase of illness or in overwhelming sepsis. The pathophysiology involves direct bacterial toxicity through say lipopolysaccharide endotoxin components of the meningococcal cell wall, cytokine release, ischaemia, vasculitis and oedema.
Meningococcal meningitis is a subtype of bacterial meningitis caused by certain serotypes of Neisseria meningitidis with highest incidence in children and particularly late adolescence. It is the second most common cause of community acquired bacterial meningitis in adults. Meningococcal disease has several other presentations and indeed with modern antibiotic therapy isolated meningococcal meningitis has a much better prognosis than meningococcal septicaemia. Most cases present with fever, meningism and a have typical characteristic rash (80%). Treatment is immediate parental administration of an appropriate antibiotic if the clinical diagnosis is suspected. Lumbar puncture can follow later semi-electively.
Vaccination is increasingly being used as a preventive measure.
Other meningiococcal disease
- Meningococcal pneumonia
- Isolated meningococcal bacteraemia
- Purulent pericarditis
- Pyogenic arthritis
- Primary peritonitis
Both meningitis and septicaemia are caused by many pathogens other than Neisseria meningitidis, its importance is that it is the commonest cause in young adults. Meningitis caused by a virus is usually a less serious illness than bacterial meningitis. Bacterial septicaemia, whatever its cause, is always serious.
Several distinct forms of Neisseria meningitidis can be distinguished by analysing the molecules in its surface coating, and the antibodies that they provoke. The commonest of these "serogroups" are known as groups A, B, C, W135, X, Y and Z.
Most disease in the UK is caused by group B meningococci, and most of the remainder by group C (although the incidence of group C disease has fallen dramatically since the introduction of universal vaccination). In the 1990s there were a number of clusters of cases associated with universities, e.g. at Cardiff and Southampton, caused by group C infections.
The incidence of meningococcal C disease has risen rapidly in the United Kingdom over the last 5 years and in 1998 was responsible for an estimated 1530 cases and 150 deaths each year with young children and adolescents at greatest risk of disease.
Mode of transmission
Neisseria meningitidis is transmitted from one person to another by droplets from the upper respiratory tract or direct saliva contact e.g. kissing. There is no reservoir other than humans and the organism dies quickly outside the host. Nasopharyngeal carriage of meningococci is common, with up to 10% of the general population and 25% of young people carrying one of a number of strains, some of which may not be pathogenic. Infection is almost invariably acquired from a healthy carrier rather than from a person with the disease. Nosocomial disease and infection of healthcare workers is very rare, but not unknown.
As carriage is common, and disease uncommon, Neisseria meningitidis might be considered a commensal, and factors that predispose individuals to becoming ill may be more important than exposure to the germ.
Colonisation in the throat is common and some surveys demonstrate the the organism in up to 10% asymptomatic outpatients. The annual incidence of invasive meningococcal disease in England and Wales rose in the 1980s and has remained stable in the 1990s. Although meningococcal disease can affect any age group, the highest age specific attack rates are seen in infancy; rates decline with age during childhood, with a secondary peak occurring at 15 to 19 years in England and Wales. Cases occur throughout the year, but two thirds of these occur in the winter months.
The case fatality rate of clinically recognised septicaemia caused by Neisseria meningitidis is 20%, pneumonia 9% and of meningitis 5%. It is therefore important that anyone seeking information about meningitis or septicaemia receives correct information.
Meningococcal disease may occur in outbreaks and epidemics, particularly in institutions such as halls of residence and military camps.
Most people who become colonised with meningococci do not become ill. Those who do become ill generally do so 2-5 days after first acquiring a new strain of the germ. Illness may arise within 7 days of acquiring the germ.
After carrying a meningococcus for 7 days or more, it is extremely unusual to become ill. For this reason an operational period of 7 days is taken to decide whether it is appropriate to implement preventive measures.
Period of communicability
Until meningococci are no longer present in discharges from nose and mouth.
Meningococci usually disappear from the nasopharynx within 24 hours after commencement of treatment with antibiotics to which the organisms are sensitive and which attain substantial concentrations in oropharyngeal secretions. Penicillin will temporarily suppress the organisms, but it does not eradicate them from the oronasopharynx.
Common sequelae of meningitis and meningococcal disease
Survivors of meningitis (meningococcal, other bacterial, or viral) may make a complete recovery, or may be left with varying degrees of neurological damage, especially deafness. See Bacterial meningitis for more details. Meningococcal septicaemia is often complicated by limb ischaemia sometimes necessitating amputation.