Killer bug in small number of carriers

By SIMON COLLINS

Only one in every 50 young New Zealanders carries the lethal strain of meningococcal disease that has killed 220 children and adults since 1991.

Two separate surveys of Auckland high school students and Dunedin university students have found that only a small percentage carry the killer strain, compared with about one in five who carry other strains of meningococcus.

Most of those who carry the bacteria have developed immunity to it, but pass it on to others with lower defences who succumb to the disease.

About 5400 people (0.1 per cent of the population) have caught the disease since 1991, and 1080 have suffered serious disabilities like brain damage, amputated limbs or death.

The Dunedin study of 205 Otago University students, which is still in progress, has found some kind of meningococcus bacteria in 45 students (22 per cent), including just four (2 per cent) with the killer strain.

A larger study of 1200 Auckland high school students led by Auckland University's Professor Diana Lennon has yet to be completed.

Dr Diana Martin of the Institute of Environmental Science and Research (ESR), who identified the new killer strain in 1992, said she was not surprised at the low carrier rates of the killer strain in both studies.

"I have always believed that if we had a really high rate of circulating organisms, you'd have a disease peak that might go much more like an influenza virus, rising to a very high level quickly and then coming down," she said.

In contrast, the "B" strain appeared in 1991, rose slowly to affect just over 600 people in 1997, and has continued to hit around 500 to 600 people every year since then.

The bug has many more carriers than the number who get ill from it because most older people become immune to it.

The main victims are babies, who are too young to have developed immunity, and young people aged 15 to 25, where there is more "social mixing".

"They are much more likely to be in close personal contact in terms of parties and the other activities that are more common in 15 to 25-year-olds," Dr Martin said.

She defended the Government's policy of vaccinating all young people rather than seeking out those who carry the bug.

"There is such a variety of meningococci that if they are living with the organism and it's not causing any disease, then it's costly to give antibiotics.

"That would be a misuse of antibiotics because antibiotics act on other organisms as well as meningococcus, and then you increase the potential of resistance to antibiotics in other bacteria."

She said scientists did not know why some people failed to develop immunity, apart from a few who had deficient levels of "complement", a group of chemicals which regulate the blood and liver.

"There is no reason to believe that anyone is, by racial background or age or anything, more likely to get the disease than others, except that very young people get it because they haven't developed natural immunity."