An outbreak of Escherichia coli O157:H7 linked to romaine lettuce from the Yuma growing region in Arizona has spread to 35 states in the United States, bringing the total cases to 197 as of 1 June 2018.1 Five deaths have been reported since the outbreak began in March 2018; 89 people have been hospitalised, including 26 who developed haemolytic uraemic syndrome (HUS) – one of the most serious complications of E. coli O157:H7 infection.1,2 This outbreak is reported to be the largest E. coli O157:H7 outbreak in the United States in more than a decade.
The US Food and Drug Administration (FDA) – working closely with federal, state and local health officials – identified romaine lettuce from Harrison Farms as the common food source that caused the initial outbreak in an Alaskan correctional facility – although Harrison Farms cannot be tied to the other cases, and it has yet to be determined where in the supply chain the contamination occurred.2 Outbreak investigation was complicated by the following two factors: products that have caused illness were no longer available at exposure locations, and a single production may have contained romaine lettuce from multiple ranches.2
The incubation period of the pathogen ranges from 1 to 9 days during community outbreaks.6 E. coli O157:H7 infection can present across a broad clinical spectrum – ranging from asymptomatic infections to death. In some cases, patients present with self-limiting, non-bloody diarrhoea without further complications; in other cases, bloody diarrhoea may develop – known as haemorrhagic colitis – the only manifestation of E. coli O157:H7 infection.3,6 About 5–10% of haemorrhagic colitis may progress to HUS – a condition characterised by microangiopathic haemolytic anaemia, thrombocytopenia, and kidney failure.2,3,6 Antibiotics are not recommended until diagnostic testing can be performed and E. coli O157:H7 infection is ruled out, as antibiotics might increase the risk of the patient developing HUS.1
The harvest season is over, and the last shipments of romaine lettuce from Yuma were harvested on 16 April 2018 – thus it is unlikely that the product is still available in people’s home, stores or restaurants due to its 21-day shelf life.1 Outbreak investigation is still ongoing.