Meningitis outbreak is not epidemic, doctor says

IRELAND is not experiencing a meningitis epidemic despite a recent rapid rise in the number of cases nationally, according to a consultant microbiologist.

"This is a point that is always difficult to get across," stated Dr Mary Cafferky, director of the meningococcal reference laboratory at Temple Street Hospital, Dublin. The laboratory collates the incidence of all types of meningococcal infection.

This bacteria is widespread in the population but seldom causes infection. It is highly dangerous when it does, however, and can lead to invasive infection of the brain lining, meningitis, or infection of the bloodstream, septicaemia.

Incidence tends to rise and fall, but there "has been a trebling of cases since the late 1980s", Dr Cafferky said. Accurate figures are often difficult to assemble because of a poor level of notification, although "notification is better than it was".

Ireland nationally has a "typical" rate of about 2.3 cases per 100,000 of population, she said, but this is now running at about 5.9 per 100,000 on average. The Eastern Health Board catchment has the highest meningococcal infection rate and this reached 8.5 per 100,000 in 1995.

The Southern Health Board rate is 7.9 and the lowest is the Northwestern Board, with 0.5 per 100,000.

Meningococcal disease is referred to as endemic when it occurs at its typical rate, Dr Cafferky said, but its current increased rate is known as "hyperendemic". It is categorised as such when cases remain sporadic and random, with the usual mix of infectious meningococcal forms appearing.

It becomes epidemic when the number of cases escalates rapidly, with patients tending to suffer from the same form of the bacteria. The age profile of patients also changes, moving from the typical one to five years age group to adolescents and young adults.

These changes are not taking place and the pattern remains random, Dr Cafferky said. "In an epidemic you get a great shift in the number of cases," but this is not currently the case.

What is changing is the pattern of illness and mortality caused by meningococcal infection, she said. Meningitis used to pose the greater risk of mortality but people are more aware now and seek treatment sooner. Septicaemia seems now to pose a greater risk and, of the 19 meningococcal disease fatalities in 1995, 13 were septicaemia.

Earlier, Dr Edward Kaczmarski, director of the meningitis reference unit of the Public Health Laboratory Service in Manchester, outlined the value of carrying out genetic typing of the organisms causing illness.

It is valuable for medical staff treating a meningococcal outbreak to know the type of bacteria involved, he said. For example, vaccination can be administered for type C infection, but this is not an option with type B.