In November 1996, a butcher who had been in business 28 years in the little town of Wishaw, southeast of Glasgow, used the same utensils to handle raw and cooked meat.

As a result of cross contamination in that single meat shop, more than 400 people became ill and 21 died from E. coli O157:H7 infections in what the British press often cite as the world’s worst recorded outbreak of E. coli food poisoning. 

The outbreak led to increased scrutiny and tracking of E. coli OI57 in Scotland, which has given researchers a unique chance to review data collected over many years–from 1999 to 2008–in an entire population.

What they found, as reported in the March edition of Emerging Infectious Diseases, was that about 11 percent of  E. coli O157 infections in Scotland were  “secondary infections”–from person-to-person contact rather than from eating contaminated food–a higher incidence than was previously assumed.

There could be several explanations for this, the authors note. Scotland’s heightened awareness and surveillance of the dangerous pathogen could have led to more assiduous contact tracing, for example. So they warn against extrapolating the results of this close look at E. coli in Scotland to other countries.

But the study does indicate that far from being unusual, secondary infections, in which one person transmits the bug to others, are common. There is a significant chance that someone beyond the person who ate a contaminated product may fall ill. It’s challenging to maintain good hygiene in cleaning up the diarrhea and vomiting that accompany food poisoning, but a lapse can tragically lead to additional infections among family members, co-workers, class mates, or fellow residents in an institutional setting like a nursing home.  

The researchers also conclude from the Scotland data that:

— Most of the secondary case patients were younger than primary case patients.

— Child to child transmission accounted for 72 pecent of the secondary cases, child to adult 19 percent and adult to adult 9 percent.

— Twelve percent of those whose E. coli infections advanced to hemolytic uremic syndrome (HUS), a potentially life-threatening complication, were secondary cases.

— Of the 88 secondary cases in outbreaks, 65 percent lived in the same household as the primary case. 

The authors recommend increased efforts to prevent secondary transmissions of E. coli within households, giving patients and their families immediate advice about infection control at home and beyond. And they encourage health authorities to continually raise public awareness of E. coli infection as a communicable disease.

“This would reduce not only the overall health and social costs of E. coli O157:H7 infection but also the number of, and distress to, HUS cases attributable to secondary spread,” the authors state.