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

1. coli O157:H7 – one of the most important foodborne pathogens – is the most frequently isolated serotype of enterohaemorrhagic E. coli (EHEC) that produce Shiga toxins.³ In the United States, the most common route of transmission for E. coli O157:H7 infections is via consumption of contaminated food or water⁴ – although direct person-to-person transmission has also been reported.⁵

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.

References

1. Centers for Disease Control and Prevention. Multistate outbreak of E. coli O157:H7 infections linked to romaine lettuce. Available at: https://www.cdc.gov/ecoli/2018/o157h7-04-18/index.html. Accessed June 2018.
2. S. Food and Drug Administration. FDA Investigating Multistate Outbreak of E. coli O157:H7 Infections Linked to Romaine Lettuce from Yuma Growing Region. Available at: https://www.fda.gov/Food/RecallsOutbreaksEmergencies/Outbreaks/ucm604254.htm. Accessed June 2018.
3. Lim JY, et al. J Microbiol Biotechnol 2010;20:5-14.
4. Rangel JM, et al. Emerg Infect Dis 2005;11:603-609.
5. Heuvelink AE, et al. Epidemiol Infect 2002;129:295-302.
6. Su C, Brandt LJ. Ann Intern Med 1995;123:698-714.