From E. coli-tainted romaine lettuce to Salmonella in cereal, this year certainly had its fair share of foodborne illness outbreaks. Health warnings had consumers discarding bags of lettuce, searching their cupboards for recalled cereal and avoiding premade wraps at grocery stores.

All of this might have left you wondering: Why did we seem to have so many foodborne outbreaks in 2018?

Experts say that, although we heard a lot about foodborne disease in 2018, it doesn't mean that we had any more outbreaks than usual. Indeed, it's likely that the U.S. always has about the same number of outbreaks every year, said Benjamin Chapman, an associate professor and food safety specialist at North Carolina State University. But critically, health officials are getting better at detecting these outbreaks, Chapman said, leading to an increase in reported outbreaks in recent years.


"The science is getting better, and the public health resources are getting better, and we're just getting better at finding things," Chapman told Live Science. [Top 7 Germs in Food that Make You Sick]

String of outbreaks

Perhaps the most notable outbreak of 2018 involved romaine lettuce contaminated with a strain of E. coli bacteria known as E. coli O157:H7. The outbreak, which began in March and ended in June, killed five people and sickened more than 200 others in 36 states, making it the largest U.S. E. coli outbreak in over a decade, according to the Food and Drug Administration (FDA). The contaminated lettuce was tied to the Yuma growing region of Arizona, and at one point, health officials advised consumers to avoid all romaine from this region.

In November, consumers had déjà vu when officials again warned people not to eat romaine lettuce due to an E. coli outbreak, this time linked to lettuce from Northern and Central California.

There were also two large outbreaks of the parasite cyclospora, tied to McDonald's salads and Del Monte vegetable trays, leading to more than 760 illnesses total, according to the U.S. Centers for Disease Control and Prevention (CDC).


Beyond produce, there were outbreaks tied to highly processed foods, including a Salmonella outbreak tied to Kellogg's Honey Smacks cereal that sickened 135 people in 36 states, according to the CDC.

And although these outbreaks made headlines, there are hundreds more outbreaks that we don’t necessarily hear about that get investigated and reported every year. (An outbreak refers to an instance when two or more people get the same illness from the same contaminated food or ingredient, according to the CDC.)

Indeed, according to the CDC's National Outbreak Reporting System, which summarizes data on U.S. reports of foodborne illness, there were about 4,000 foodborne illness outbreaks each year from 2012 to 2016, (the most recent years for which data is available). That's up from only about 1,000 reported outbreaks in 2008.

That "looks like this big jump" in outbreaks, Chapman said. But the increase is really due to health officials getting better at "connecting the dots" to find more foodborne illness outbreaks, he said. In other words, the outbreaks were happening, but health officials just weren't as good as detecting them.

Improved detection

One technological advance that has led to improvements in foodborne outbreak detection is the ability to sequence the whole genome of the microbe causing the illnesses. This means that two seemingly sporadic cases in different parts of the country can be connected if they are caused by genetically identical microbes.

"It's the sequencing of the strains that's given us the degree of confidence [to say] a case here, a case there, a case over there, have got to have something in common," said Dr. Robert Tauxe, director of the CDC's Division of Foodborne, Waterborne and Environmental Diseases, who spoke with Live Science at a conference in October on infectious diseases.

But beyond advances in technology, there's also been an increase in the capacity of health departments to investigate outbreaks, Tauxe said.

Indeed, in recent years, state and local health departments have received an increase in resources, in the form of money and expertise, to collect data and investigate foodborne illness outbreaks, Chapman said. There are conversations every day between state and federal teams about specific illnesses that are happening in the country to determine whether they are tied to an outbreak. This is the "behind the scenes world of food safety," Chapman said.

Once officials identify that people are being sickened by the same microbe, they have to reach out to patients and conduct detailed interviews to determine whether they all ate a similar food, or have another exposure in common.

Classically, a foodborne illnesses outbreak was thought of as a group of people who all got sick from eating the same food at the same place at the same time, Tauxe said. But with advances in foodborne outbreak detection, "our interpretation of what an outbreak is, is starting to broaden," Tauxe said. An outbreak might be caused by more than one food, or have more than one source; and cases may be detected over a long period of time.

For example, the E. coli outbreak tied to romaine lettuce from Yuma was never traced to a single source or farm. Instead, investigations pointed to several dozen farms as potentially supplying the contaminated romaine lettuce. Samples of irrigation canal water in Yuma tested positive for E. coli O157:H7, leading investigators to conclude that the canal water likely contaminated the lettuce, according to the FDA. But exactly how the water contaminated so many farms that were miles apart is unclear. One hypothesis is that the canal water may have been used to dilute pesticides that were used in "aerial spraying," or crop dusting.

Unfortunately, better detection of outbreaks means that the total number of reported outbreaks likely won't be going down anytime soon.

"As we get better at reducing risk [of foodborne illness], we also get better at finding things we didn't know were there," Chapman said. "I don't expect that we would have any less or any more outbreaks in 2019."

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Originally published on Live Science.