Shiga toxin-producing Escherichia coli (STEC) food-borne outbreaks

Abstract

Escherichia coli (E. coli) are Gram negative, non-sporulating bacteria, which belong to the normal intestinal flora of humans and animals. Shiga toxin-producing E. coli (STEC) are a group of E. coli that is defined by the capacity to produce toxins called Shiga toxins (Stx). Following ingestion of STEC, the significant risk of two serious and potentially life-threatening complications of infection, hemorrhagic colitis and hemolytic uremic syndrome (HUS), makes STEC food poisoning a serious public health problem. Besides Stx, human pathogenic STEC harbor additional virulence factors that are important for their pathogenicity. Although human infection may also be acquired by direct transmission from person to person or by direct contact of humans with animal carriers, the majority of STEC infections are food-borne in origin. The gastrointestinal tract of healthy ruminants seems to be the foremost important reservoir for STEC and ingestion of undercooked beef one of the most likely routes of transmission to humans. Other important food sources include faecally contaminated vegetables and drinking water. The serogroup classification of STEC is based on the somatic (O) and flagellar (H) antigens, and, to date, more than 200 STEC serogroups have been identified. Human STEC infections are, however, associated with a minor subset of O:H serotypes. Of these, the O157:H7 or the O157:H- serogroups (STEC O157) are the ones most frequently reported to be associated with food-borne outbreaks. However other non-O157 STEC serogroups such as E. coli O26, O103, O111, O121, O45 and O145 have caused several outbreaks in recent years. Two outbreaks of gastroenteritis caused by E. coli O157:H7 were first reported in the US, following the consumption of undercooked hamburgers, in 1982. Since then several outbreaks were reported worldwide. A major E. coli O157:H7 outbreak occurred in Japan and contaminated radish sprouts was identified as the vehicle of infection. More than 6,000 school children were affected, 101 people were hospitalized with HUS and 12 deaths were recorded. The recent outbreak of STEC O104:H4 infection and HUS reported in Germany in the spring of 2011 was one of the largest outbreaks worldwide. As of 27 July, 3126 cases of STEC infections, 773 cases of HUS including 46 deaths linked to the outbreak in Germany and occurring in the European Union (EU) (including Norway). Outside the EU 8 cases of STEC and 5 cases of HUS, including 1 death have been reported in the USA, Canada and Switzerland, all with recent travel history to Germany. The present review on major STEC food-borne outbreaks recorded worldwide highlights the need for control measures in order to prevent or at least minimize the occurrence of similar events in the future.