Here's a that recently caught my eye: "Five sick in French Listeria outbreak linked to cheese alternative." Published on January 21 in Food Safety News, the report referenced four pregnant women in France who ate the same Listeria-tainted, plant-based food, then suffered serious infections and delivered prematurely. The sole upside? According to current intel, the novel "fromage" containing almond milk and organic cashews has not yet caused a Listeria-related death.
Well, that's one more infection vehicle for the books, I thought. At the same time, I recalled some of the many foods previously defiled by Listeria. The official list begins in the early 1980s with shredded cabbage from pale, green heads fertilized with sheep manure (a potential source of Listeria), then stored in a cold shed. The resulting outbreak traced to slaw claimed 18 Canadian lives and produced a in the New England Journal of Medicine. The outbreak also solved a mystery, at long last confirming that Listeria entered humans via food.
Then came a slew of reports as the following decades saw Listeria sepsis and meningitis stemming from everything from soft, unpasteurized cheeses to alfalfa sprouts, packaged salads, caramel apples, smoked fish, and deli meats -- even frozen vegetables and ice cream.
Nonetheless, it was the U.S.'s worst-ever Listeria outbreak -- the 2011 multi-state debacle traced to cantaloupes from Colorado -- that inspired today's title. One year later, after 33 people had died, a noted Listeria expert was invited to a mid-day caucus on Capitol Hill. "I hate to spoil your lunch," said UC Berkeley professor Daniel Portnoy, PhD, as he started to , some of them wolfing sandwiches, "but it's likely you're eating Listeria. Because it's everywhere."
Tracking a Sporadic Killer
Looking back, Listeria has a as well as unique clinical and ecologic features. In the 1920s, it was first isolated by a bacteriologist at Cambridge University after it killed six of his laboratory rabbits. In 1940, a noted English physician re-named the bug , the famous 19th century surgeon who championed surgical hygiene. Paradoxically, Listeria itself later surfaced in many earthy haunts such as soil, streams, rotting vegetation, and ruminants' guts. A final peculiar trait was its cold-enhanced growth (this explains why Listeria can still proliferate, albeit slowly, in refrigerated foods).
Additional came in 1949 when the tiny bacillus grew from autopsied organs of malnourished infants in Germany. In retrospect, did the children's semi-starved state increase their risk of a fatal attack? Undoubtedly, yes. But what subsequently became clear was Listeria's delicate dance within many immunocompromised patients, sometimes producing (after an unusually long incubation) a cruel invasion of meninges and brain. In short, while some of us eat Listeria and never know the difference, the ubiquitous bug can also kill and maim the very young, the very old, or people with weakened immunity caused by various diseases and treatments.
Finally, pregnancy is a special, high-risk condition, which currently accounts for invasive infections with Listeria. This brings me to another seminal outbreak I witnessed first-hand while serving as the sole infectious diseases specialist at a small county hospital in Los Angeles.
A Septic Miscarriage in My Own ED
The year was 1985, and I was a young assistant professor and ID Chief at UCLA-Olive View Medical Center when I was urgently paged by a third-year resident. By then, I already knew that a recently-admitted patient had Listeria in her blood.
Long story short: 2 nights earlier, the future obstetrician calling "SOS" had been heavily splashed in the face with that same woman's amniotic fluid while delivering her 20-week stillborn in our emergency department (ED). Now he reported fever, flu-like aches, and reddened eyes. Considering his exposure, I started him on amoxicillin. A day or two later, he was fine.
The grieving patient, on the other hand, required several days of IV ampicillin before her fever abated and she was well enough to go home. In the meantime, we wondered: How the heck had she contracted Listeria in the first place?
Fast forward another 3 months and the answer finally emerged after Los Angeles staggered through case after case of listeriosis and county health workers frantically sought its source. At long last, one sufferer's fridge yielded an open package of queso fresco cheese that grew the outbreak strain, as did another sealed package purchased from a store. That's when the tainted food was recalled, the factory shuttered, and public safety restored.
But by then, Listeria had mauled 142 mostly-Hispanic patients, killing nearly .
As to the cheese's manufacturer, Laurene Mascola, MD -- then a health department rookie who would later become our county's Chief of Acute Communicable Diseases -- could only express sadness and dismay. Not only was the Jalisco food products' plant awash in listeria, some of its workers never pasteurized their product's main ingredient. "They had no idea of science," Mascola later told me. "They just thought a little bit of raw milk made the cheese taste better."
Parting Lessons From Listeria
Some believe it's hard to educate doctors, and even more so the public, about the myriad causes and sources of foodborne infection. But I disagree. Because everyone eats, and every year, suffers a foodborne blight, I believe it's a highly-relatable topic. Plus, it's a great way in to pique interest in foodborne infection prevention by anyone from a healthcare professional to a kid in junior high.
Listeria is a great case in point. Who among us wouldn't want to make sure someone vulnerable -- say, a pregnant relative or a fragile, immunocompromised elder -- didn't understand this potentially deadly pathogen?
Today, studying foodborne infections also shows how new techniques like can crack elusive outbreaks like long-running contamination by Listeria.
But here's my message to healthcare professionals in particular: Don't expect Listeria to disappear any time soon. Thanks to its affinity for modern, refrigerated foods and cold environs, it will always pose a threat. Staying abreast of old and new vehicles of Listeria through a service like is one way to stay savvy; simply mentioning foodborne infections to high-risk patients, or referring them to a CDC website, is another way to raise awareness and promote safer eating.
In fact, just a couple of weeks ago, the CDC announced a new of Listeria. As of this writing, its source is still unknown.
Claire Panosian Dunavan, MD, is a professor of medicine and infectious diseases at the David Geffen School of Medicine at UCLA and a past-president of the American Society of Tropical Medicine and Hygiene. You can read more of her writing in the "Of Parasites and Plagues" column.