An Austrian outbreak of Salmonella enteritidis phage type 36 in 2004

In June 2004, an egg packing station was epidemiologically incriminated as possibly distributing the vehicle of the Salmonella enterica subsp. enterica ser. Typhimurium definitive type (DT) U291 outbreak which began in September 2003 and--as of June 2004 affected more than 100 persons all over Austria and 8 German tourists. A total of 68 egg producing farms were screened for salmonella. Whereas all samples tested negative for S. Typhimurium DT U291, one batch of laying hens was identified as being heavily contaminated with a rare Salmonella enterica subsp. enterica ser. Enteritidis phage type, namely PT 36. This phage type was cultured from 6 of 7 swabs from pooled fecal samples (drag swabs), from 1 of 4 samples of pooled yolks, and from 7 of 11 hens tested (ovaries, liver and intestinal content pooled per hen). In 2004, a total of 36 culture-confirmed human PT 36 infections (19 manifest cases, 12 asymptomatic carriers, and 5 excreters with unknown clinical status) were documented in 4 of the 9 Austrian provinces. It was possible to demonstrate that eggs from this single farm were the probable source of infection for 30 of 31 culture-confirmed human infections. Only in the case of one patient, who regularly purchased eggs at the local market, could no connection to the farm be proven due to inability to trace the market's egg source. The PT 36 outbreak ceased after elimination of the contaminated flock. This episode underlines the considerable potential of adequate epidemiological and microbiological investigations of food-borne outbreaks to improve prevention and control of communicable diseases. The source of the S. Typhimurium DT U291 outbreak--which initially prompted this investigation--is still not identified and accounts for more than 300 human cases until August 2005.