Romaine lettuce and E coli: all you need to know

The CDC sent out a rare alert advising against consuming romaine lettuce in the second high-profile contamination this year

The US Centers for Disease Control and Prevention (CDC) sent out a rare, wide-ranging alert two days before Thanksgiving, advising “consumers, restaurants and retailers not to eat, serve or sell any romaine lettuce as it investigates an outbreak of E coli”.

The scare is the second high-profile contamination of romaine lettuce with E coli this year, and comes just weeks after the US Food and Drug Administration (FDA) attempted to put the earlier outbreak to bed with a new “special surveillance” program.

The most recent outbreak highlights the difficulties investigators often face when trying to track down the source of an outbreak, and the conditions on farms that can lead to widespread contamination.

What is E coli and why is it on my lettuce?

Escherichia coli, commonly called E coli, is found throughout the environment, in food and in the guts of animals and people. Most strains are harmless, but some cause diarrhoea, pneumonia and urinary tract infections.

The elderly and children are most likely to fall ill from harmful strains. An estimated 48 million Americans are sickened by foodborne illnesses each year. When outbreaks like the current one occur, only the most severe cases tend to be found. That means more people were likely to have been impacted by the outbreak than CDC investigators know about.

Have there been other outbreaks this year?

The largest started to gain attention in June. In that case, romaine lettuce was contaminated with the same strain of E coli as the CDC warned about this week, although the agency said the outbreaks are unrelated.

This most recent E coli outbreak on romaine has the same DNA fingerprint as an earlier strain found on leafy greens in the US and Canada in 2017. During that outbreak, 25 people were sickened across 15 states. The cause of that outbreak was never found.

How could the source of the 2017 outbreak not be found?

It was very difficult for investigators with the FDA, responsible for ensuring the safety of fruits, vegetables and fish in the US food supply, to isolate the source of contaminated leafy greens.

The June outbreak in lettuce was far larger than the one the CDC warned about this week. Then, more than 200 people were sickened, 96 hospitalized and five died.

Investigators had to trace the June outbreak back through a complex, industrialized food chain which ships vegetables all over the country, often using handwritten, paper records. This prompted FDA commissioner Scott Gottlieb to call on the vegetable industry to urge “all segments of the leafy greens industry to review their operations” and modernize documents.

How do vegetables get E coli?

Root vegetables and leafy greens are most likely to be contaminated through manure applications to soil, to help fertilize crops, according to the University of Colorado’s extension program. Ruminants – such as sheep and cows – are most likely to carry E coli.

One of the reasons leafy greens might seem to be singled out is because people often eat them raw. Cooking destroys bacteria, whereas salads are often simply rinsed and served. That means raw fruits and vegetables actually sicken more people than beef and chicken, according to reporting from Vox.

In the June case, once investigators tracked the lettuce through those handwritten records, they found a likely source: a nearby irrigation canal that workers used to dilute chemicals such as pesticides, and which was adjacent to a factory farm where animal waste would have been present.

Are these outbreaks happening more often?

Not necessarily. The US has just been testing more frequently. That can lead to an increase in incidence, without an increase in the scale of the problem.

Does the US have a safe food system?

According to independent groups such as Oxfam America, which assessed this question in 2014, the US ranks 21st out of 125 countries in overall food health, availability and safety (as measured by access to safe water). That is below other European nations, such as France and the United Kingdom, which ranked second and 13th, respectively.

What is the FDA doing about this?

Problems with romaine lettuce have become so frequent, the FDA announced a “special surveillance” plan to sample lettuce for contamination in early November.

The outbreak that led to this most recent warning has sickened 13 people across 11 states. One victim has developed a type of kidney failure called hemolytic uremic syndrome from the exposure.

Although romaine lettuce is not typically the star of a Thanksgiving meal, it is important to follow CDC advice and avoid romaine lettuce until further notice.