Salmonella and E. coli now seem to be household names, while listeria is not.
Listeria monocytogenes, one of six listeria bacterial types, is the bad guy, a nasty bug, though less common than the aforementioned two. Listeria infects horses, cattle, sheep, even poultry and swine, and from these species, it can enter the human food chain. The disease in animals and humans is known as listeriosis.
Listeriosis has a rather long incubation period. From the time of ingestion of contaminated food products to the appearance of clinical disease may take up to six weeks. As a result, it is difficult to trace exposures, and isolated illnesses may fall under the radar. Epidemics, or outbreaks, such as happened with cantaloupes from eastern Colorado and recently with Blue Bell ice cream, are more readily visible.
Listeriosis has long been known to veterinarians: It causes “circling disease” in horses, cattle and sheep. Because one side of the brain is often affected, sheep may have a drooping eyelid, ear and lip on the affected side and walk in circles or lean against fences or walls when weakened. However, this is not the picture for humans. (Some of us may walk in circles but not from listeriosis.) Although the disease is primarily a food-borne illness, it can be contracted from sickened animals. Human-to-human transmission is said to be very rare.
While listeria is found in the stomachs of about 5 percent of the population, it only causes clinical disease in 10 people per 1 million each year – a few thousand cases in the U.S. annually. That’s the good news. Those at greater risk are the elderly, those with compromised immunity and those with reduced stomach acidity.
Listeria infection often hits the bloodstream (sepsis), causing sudden-onset fever, aching, nausea, vomiting and diarrhea. Patients are recognizably sick, and listeriosis is virtually indistinguishable from other causes of sepsis. Listeria meningitis also occurs. Pregnancy-associated listeriosis is fortunately a milder infection and is more common in the third trimester. Premature delivery and fetal demise may result if diagnosis and antibiotic treatment are not prompt and appropriate.
The Centers for Disease Control and Prevention first began tracking outbreaks of listeria food poisoning in the 1970s. The worst such event was in 1985: 52 deaths, including 19 stillbirths and 10 infant deaths from Mexican-style soft cheese made in California. In 2011, the Holly outbreak killed 30 of 147 confirmed cases in 25 states. The victims’ ages ranged from 48 to 96 years; the median was 82.5.
I must admit to having been somewhat cavalier about washing fruits and vegetables – not anymore. Consider avoiding “raw” hot dogs, rare-cooked meats, soft cheeses and unpasteurized dairy products.
www.alanfraserhouston.com. Dr. Fraser Houston is a retired emergency room physician.