Aug 5, 2011 (CIDRAP News) Two Eurosurveillance reports yesterday shed new light on secondary infections in Europe's Escherichia coli O104:H4 outbreak, suggesting that the pathogen isn't more transmissible than other similar strains and that it can lose its extended-spectrum beta-lactamase (ESBL) resistance.
One of the reports is a study on secondary E coli O104:H4 infections in Germany's Hesse state, an area that wasn't at the epicenter of the outbreak but did report some illness clusters, along with infections in people who had traveled to northern Germany, where he epidemic originated. The other is a report on infections in a French family that had a link to that country's illness cluster in Bordeaux.
In the German study, researchers explored Shiga toxin E coli (STEC) and hemolytic uremic syndrome (HUS) cases that were reported between May 1 and Aug 2 to health authorities in Hesse. They found that 55 HUS cases and 81 STEC cases met the E coli O104:H4 outbreak definition. Clusters were linked to a company-run cafeteria and two private parties. Sprouts served at the cafeteria and one of the parties were linked to the north German farm identified as the source of the contaminated sprouts.
The researchers determined that 8 of the STEC cases and 1 of the HUS cases were probably secondary cases. Six of these were in family members, two were nosocomial infections, and one was a laboratory-related infection.
The authors say the findings suggest that E coli O104:H4 can be easily transmitted but is not more transmissible than other STEC strains. For E coli O157:H7, for example, secondary transmission has been reported in 4% to 15% of households following sporadic cases, they report.
In the report from France, researchers explored E coli O104:H4 transmission in the family of a man who was part of the Bordeaux illness cluster, in which sprouts grown from contaminated seeds sickened nearly a dozen people. The man had consumed spouts during an open house at a children's community center that his daughter attended.
Household transmission was confirmed in the man's daughter, who attended the event but did not eat sprouts, and his wife, who did not attend. The pathogen was isolated from her stool sample, but it did not contain genetic evidence of ESBL resistance, a characteristic of the outbreak strain.
Dr A.W. Friedrich, a microbiologist at the University of Groningen in the Netherlands, wrote in an accompanying Eurosurveillance editorial that the two secondary transmission reports help answer some of the many questions that arose during the outbreak.
He wrote that the ESBL finding in the French secondary transmission case confirms the known mobility of plasmids that carry resistance genes.
"This fact should be taken into consideration in diagnostic laboratories if ESBL resistance of EHEC O104:H4 is used for primary selection of the pathogen from stools without using also non-selective enrichment and detection of Shiga toxin genes," Friedrich wrote.
He added that the German report helps clarify three important issues: that secondary E coli O104:H4 transmission isn't more frequent than expected, that screening found other E coli serotypes, showing the need for more rapid subtyping methods, and that infection control precautions are crucial in hospital and lab settings.
The outbreak and the new findings serve as a reminder that though the E coli O104:H4 epidemic is over, the world needs to be better prepared to handle the next large outbreak, Friedrich wrote.
See also:
Aug 4 Eurosurveill report on German secondary cases
Aug 4 Eursurveill report on French family transmission
Aug 4 Eurosurveill editorial
