Slide 1: Epidemiology and public health management of meningococcal disease in the UK

Slide 2: Epidemiology of meningococcal carriage and disease Neisseria meningitidis, the meningococcus, is a normal inhabitant of the human nasopharynx and is transmitted from person to person by droplets or secretions from the upper respiratory tract.

Slide 3: Meningococci are classified according to characteristics of the polysaccharide capsule (serogroup), outer membrane proteins (serotype and serosubtype) and chromosomal DNA (genotype).

Slide 4: Carriage of meningococci (all strains included) is relatively common. A large community survey in England in 1986 found carriage rates varying from 2% in children under 5 years to a peak of nearly 25% in 15 to 19 year olds. The average duration of carriage is around one to one and a half years. Increased rates of meningococcal carriage have been observed in smokers, overcrowded households and military recruits.

Slide 5: There are many different strains of meningococci. Most are harmless and help to build up immunity. The few strains that are virulent cause nearly all cases of serious disease. When someone acquires a virulent strain, they may be already protected through existing immunity, they may build up immunity to that strain or, more rarely, they may develop disease. The incubation period is usually 3-5 days.

Slide 6: In the UK, annual rates of invasive disease vary between 2 and 10 per 100,000, with case fatality rates around 10%. Most cases are caused by serogroup B or C strains. Disease usually presents as septicaemia, meningitis or both. Age specific attack rates are highest in infancy, and decline during childhood with a secondary rise in teenagers and young adults. The highest incidence is seen in the winter months.

Slide 7: Risk factors for meningococcal disease Risk factors include passive smoking, preceding influenza and overcrowding: Passive smoking Passive smoking is an important risk factor for meningococcal disease because smoke damages the nasopharyngael mucosa. Therefore, those that live in a smoky environment may be more susceptible to acquiring the meningococci and are at more risk from disease. Preceding influenza Influenza can reduce the host's resistance to infection by an effect on the immune system thus increasing susceptibility to meningococcal disease. Overcrowding Overcrowding is a risk factor because transmission via close prolonged contact is more likely to occur in these conditions.

Slide 8: The incidence of meningococcal disease rose to high levels during 1998/99, particularly associated with serogroup C strains. Following the introduction of the UK meningococcal C conjugate vaccination programme in November 1999, there was a marked fall in disease caused by serogroup C strains.

Slide 9: Early treatment Early treatment of suspected cases with benzylpenicillin is recommended in the UK to reduce case fatality. The recommendation is based on the rapid clinical deterioration that can occur in meningococcal disease, on the established effectiveness of penicillin in hospital treatment and on the evidence for lack of harm. Adverse effects from benzylpenicillin are unusual. Anaphylactic reactions are rare, occurring in 1 in 7,000 to 1 in 25,000 of treated patients.

Slide 10: Public Health Management Following a case of meningococcal disease public health management is vital. The public health doctor has the responsibility for and coordinates chemoprophylactic antibiotics and vaccination. Antibiotics are given to household contacts to reduce the risk of disease by eradicating throat carriage of virulent strains within this group. If illness in the case is due to a vaccine preventable strain (e.g. C, Y, W135) these contacts should also be offered an appropriate vaccine (unless already vaccinated).

Slide 11: As the risk of further cases is highest in the first few days, it is important to give antibiotics as soon as possible and to ensure that medical advice is sought if illness develops in family members.

Slide 12: Following a case, it is important to give out information because early diagnosis and treatment should reduce mortality. There is a small but real risk of further linked cases. Accurate and timely information helps to limit the spread of false rumors and anxiety. Information is given out on a need to know basis where public health action is required.

Slide 13: Management of clusters Outbreaks of meningococcal disease often generate high levels of public alarm Contributing to this alarm are the lack of predictability and speed of development of outbreaks that can confound the efforts of public health authorities. The speed of public health response is thus important both to implement preventive measures and reduce public anxiety. The evidence for clustering should be sought before taking action. Are the cases of similar age? Are they friends? Are they caused by the same strain? What is the interval between them? Giving out information is always advised. If there is clustering, antibiotics may be given to a group that is considered to be at higher risk of further cases e.g. all children and staff attending the same nursery as 2 cases. Vaccination is also then advised if the cases are due to a vaccine preventable strain.

Slide 14: Management of clusters in the wider community One of the major difficulties in targeting a wider community for intervention is deciding on the population boundaries, often defined by age group and geography. Such boundaries will of necessity be arbitrary. Existing administrative boundaries should be used that make sense to the people who live within and without them. In any case, there are likely to be people living on the other side of the boundary who may feel unjustifiably excluded. Although school outbreaks must be handled quickly in order to control alarm and reduce immediate risk of further cases, wider community outbreaks usually build up more slowly and by their nature are more diffuse. The same management steps apply. Reference: PHLS guidance on control of meningococcal disease. See website (www.phls.co.uk).