A regional outbreak of S. Enteritidis phage type 5, traced back to the flocks of an egg producer, Austria

In the spring and summer of 2002, the Nationale Referenzzentrale für Salmonellen (National Reference Centre for Salmonella - NRCS) in Austria noticed a cluster of human Salmonella enterica subsp. enterica ser. Enteritidis phage type 5 (S. Enteritidis PT5) infections in two neighbouring districts of Austria. Another small outbreak of S. Enteritidis PT5 infections that occurred in the same region in 1999 had been traced back to the flocks of a local egg producer (approximately 6 000 hens). Attention was therefore again directed at this farm. The results of voluntary bacteriological examinations from the farm and further epidemiological investigations identified the same egg producer as the source of the second outbreak. The 70 human isolates of S. Enteritidis PT5 ascertained in 2002 represented a minority of all infections. It is realistic to estimate that several hundred infections occurred in the course of the 2002 outbreak. The farmer had not vaccinated new flocks against Salmonella since August 2001. It is likely that the change in vaccination policy resulted in the reappearance of the S. Enteritidis PT5 infections. By the end of September 2002 the farmer had stopped selling untreated table eggs. In October 2002 only one isolate of S. Enteritidis PT5 was ascertained in the region.