Meningitis unpredictable and hard to trace, says expert

After a decade without meningitis deaths, Nova Scotia appears to have two in the space of week, with no known link between them.

The odds of that look low. However, strange-seeming coincidences are the norm for meningitis, an illness known for being unpredictable and hard to trace, says one of the country's top experts on the illness.

"It tends to come in waves," says Dr. Ronald Gold, who was head of infectious diseases at the Hospital for Sick Children in Toronto before his retirement.

"Very often you don't have a link between cases."

There is a reason that clusters of cases appear, and it lies in the fact that for every person who becomes ill with meningococcal bacteria, there are many carrying the same bacteria who don't, said Gold. 

That means infection patterns can change drastically within a certain population before those changes become obvious through illness and deaths. At that point, it can be hard to know how it all started.

Vaccines and rare strains

In one case that is better understood, a certain group of meningococcal bacteria known as "W" had been very rare worldwide, said Gold.

However, that strain of W bacteria caused an outbreak in Saudi Arabia during the Hajj pilgrimage one year, he said. Some people got sick, but many more carried the bacteria back home in their noses and throats.

"Then we had a worldwide epidemic," he said.

Suddenly the W strain became the most common meningococcal bacteria strain in parts of north Africa and the Middle East, even if there was no obvious link between each individual case by that point.

"We had very little of [that strain] brought back to Canada or the United States, but it certainly can change very dramatically like that," Gold said.

That is why it's a good idea to use the vaccines that cover rare strains instead of waiting to see if those strains become more common, said Gold, who helped develop some of the meningitis vaccines and still advises vaccine companies.

"We know they can increase, they have increased in the past, and it's better not to wait for something bad to happen," he said.

Some strains are more deadly than others, but none causes death in more than about 15 per cent of cases, assuming patients are treated.

Origin may never be known

The federal government's microbiology lab in Winnipeg receives samples of strains that appear across the country, analyzes them and looks for patterns, said Gold.

However, that process can take months and meningitis moves very quickly.

"You can have someone whose first symptom is usually fever and maybe aches and pains and a headache and not feeling well, and they can be dead within 18 to 24 hours," he said. "There are very few bacterial infections that can kill people as quickly as this can."

It's also common for cases to follow each other quickly because meningitis has a season, just like flu season, Gold said. In fact, meningitis often follows on the heels of flu outbreaks.

"The damage from the virus may make it easier for the bacteria to infect people in their nose and throat," he said. "It's a pretty well-known link and probably explains why the meningitis does peak usually in January, February, March."

Nova Scotia will begin using a more comprehensive vaccine next year. In the meantime, researchers are trying to learn if the same strain of bacteria was responsible for both recent deaths, said chief public health officer Dr. Robert Strang.

"That's an important piece of information," he said.

However, if there does turn out to be a new pattern of infection in Nova Scotia, its origin may never be known.

In the two recent cases, "it's virtually impossible to track down the sources, because it could be anyone in the public who could be one of these carriers," said Strang.