September 17, 2004

'Flesh-eating' bacteria are on the rise

European monitors reveal prevalence of fatal infections.

by Alison Abbott
Nature News

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The harder you look, it seems, the more you find... and it won't always be good news. A European research network has found that life-threatening infections with group A Streptococcus, also known as 'flesh-eating bacteria', are much more frequent than had been thought.

Scientists in 11 countries, led by microbiologist Aftab Jasir at Lund University in Sweden, have been systematically searching for these infections. When they started the project in 2002 they expected to find 1,000 cases in the first 18 months. Instead they found 5,000.

"There had been little surveillance in countries like Italy, Cyprus and Romania," says Jasir. These countries initially claimed they had very few cases. "But when everybody started to look systematically, it turned out that the incidence was more or less the same everywhere: between 3.8 and 4 cases per 100,000 population."

Most group A streptococcal infections are benign. They may cause a sore throat or there may not be any symptoms at all. But in some cases the bacteria mysteriously turn rampant. They invade the body and chew through soft tissue and muscle, damaging the heart or kidneys, a condition known as necrotizing fasciitis. In other cases, they tear holes in fine blood vessels, causing leakage of fluid and a precipitous fall in blood pressure, called toxic shock syndrome. Death can strike within 24 hours, and it does so in 20-30% of cases, even with high-dose antibiotic treatment.

Evolving strains

Jasir suspects that the 25 countries of the newly expanded European Union harbour up to 20,000 cases each year. And she says that evidence from countries where surveillance has always been most efficient, such as Britain, Scandinavia and the Czech Republic, suggests that the incidence rates are increasing. "In Britain alone, the number of reported cases has doubled in the past five years," she says.

Another worrying sign is that, among the collected strains, the researchers found a huge number of distinct types of bacterium, which differed in the structure of a particular protein. This protein, called 'M', alerts the host's immune system to the bacterium's presence. This diversity implies that the bacteria are evolving rapidly.

Scientists do not understand what the evolution of the strains will mean for the incidence and treatment of infections in the future. But they know that the number of different types will make developing a vaccine difficult. Given this, alongside worries that the bacteria may develop resistance to the powerful antibiotics that keep many sufferers alive, scientists are pushing for more research into the basic biology of the catastrophic infections.

As yet they have little idea about what makes a benign group-A Streptococcus strain suddenly turn virulent. Some strains seem to have more potential to become aggressive, but the state of the patient's immune system also seems to be an important factor. "Understanding the biology of this is the next priority for the research network," says Jasir.

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