SCIENCE: Vital clues to a mystery killer

Microbe of the Month: What became of the flesh-eating bug? Bernard Dixon investigates

Whatever happened to the flesh-eating microbe? During the first five months of 1994, the bacterium Streptococcus pyogenes caused five cases of necrotising fasciitis (NF) - so called because it kills tissues such as the sheaths (fascia) around muscles - two of them fatal, in west Gloucestershire. "Killer bug ate my face" was typical of the headlines spawned by the virulent microbe. The incidents were peculiarly nasty. Moreover, five cases in a population of 320,000, where the condition had been unknown for at least a decade, was surprising.

Two years later, some answers to the worrying "flesh-eating bug" affair are available, thanks to an analysis of the incident in the current issue of Epidemiology and Infection. The report identifies the likely origin of two of the cases. It also provides guidelines for reducing the risk of a similar occurrence. But it still leaves an element of mystery as to why several cases of a rare condition should have occurred in one area in such a short space of time.

The report presents compelling evidence that the first two NF patients acquired their infections during surgery in the same operating theatre, probably from the throat of a member of the theatre staff. The first patient had a routine hernia operation in February 1994 at a hospital serving the Stroud area. He became feverish the next day, collapsed 36 hours after surgery, and developed the gangrenous changes that characterise NF. Despite intensive treatment with antibiotics, large areas of skin had to be cut away. Four days later, another patient became similarly ill after a varicose vein operation. Again, doctors administered antibiotics and excised the affected tissues. Technicians screened the tissues for microbes and found that they carried S pyogenes, which can cause NF, usually in people who are vulnerable to infection.

At this stage, the hospital authorities closed the operating theatre for cleansing, and took nose and throat swabs from people working there. One staff member proved to be heavily infected with S pyogenes. Subsequent tests showed that the S pyogenes carried by the staff member was of the same type as that in the dead flesh from the second patient. Re-examination of the tissues of the first patient indicated that they also carried the same organism.

In the light of the Gloucestershire incident, the report's authors recommend that any cases of NF developing after surgery should be investigated carefully to determine whether S pyogenes is responsible. They also conclude that, while there is no need for an operating theatre to be closed after one case of NF, the occurrence of two or more cases does warrant immediate closure and investigation of staff.

So why did S pyogenes cause five confirmed cases of NF in one area in such a short space of time? How to account for the infections that were not acquired in hospital? There is no evidence that anything made the people of west Gloucestershire more prone to bacterial infections during the early months of 1994. Perhaps, therefore, the "cluster" of cases arose by chance.

The final possibility is that some genetic change occurred in the bacterium itself. This would have had to affect each of the four different types of S pyogenes - which seems unlikely but could have happened. In that case, we face one of the trickiest questions of all. Why did the "outbreak", if it really was an outbreak with a common cause, come to an end?