Listeriosis is an infectious disease which, nearly always, is caused by the consumption of food or drink that has been contaminated with L. monocytogenes. Approximately 2,000 cases of listeriosis are reported each year in the United States. The actual incidence, however, may be substantially higher. Recent research has indicated it is very likely that a large number of listeriosis cases either do not get reported or are misdiagnosed. Like most other foodborne illnesses, listeriosis is susceptible to being underreported because its symptoms are often very mild. Misdiagnoses are common because an accurate diagnosis of listeriosis requires: (1) the infected human to seek medical help; (2) the physician to instruct the patient to submit a stool sample, and (3) the stool sample to be analyzed at a laboratory. Armed with the results of such test, an accurate diagnosis can be made.
The Listeria bacterium consists of seven unique species: L. grayi, L. innocua, L. ivanovii, L. monocytogenes, L. murrayi, L. seeligeri, and L. welshimeri. L. monocytogense is the only specie likely to cause any physical symptoms in humans. It is estimated that L. monocytogenes causes as many as 98% of all human cases of listeriosis.
LISTERIA HAS HIGH HOSPITALIZATION RATE
Although Listeria is the one of the least reported causes of foodborne illness in the United States, the cases that do get reported most often require hospitalization. Listeria infections cause approximately 250-500 deaths and 1,500 hospitalizations per year. With 1,500 hospitalizations stemming from 2,000 annual cases, Listeria has the highest hospitalization rate of all foodborne pathogens at approximately 75%.
LISTERIA NOW RECOGNIZED AS A DEADLEY THREAT
Listeria was originally thought to be almost exclusively related to animals. When L. monocytogenes was first discovered over 80 years, there was not much reason to suspect that it could cause disease in humans. Only recently has Listeria garnered public awareness as it was first identified as a cause for foodborne illness in 1981. Then, just two years later, in 1983, the first Listeria outbreak was confirmed in Canada.
Shortly thereafter, in 1985, Listeria caused what was one of the deadliest foodborne illness outbreaks ever in the United States. Over 142 cases of listeriosis were linked to eating soft, Mexican-style cheese. Of those sickened, 93 were pregnant women. Overall, 28 people died, including 10 newborns and 18 adults.
The year 2011 brought an even deadlier outbreak of Listeria. Listeria-contaminated cantaloupe produced by Colorado-based Jensen Farms ultimately caused the death of over 32 people and resulted in one miscarriage. It has the dubious distinction of killing more people than any other foodborne outbreak in the US.