Salmonella is a Gram-negative, rod-shaped bacterium. Alongside the likes of E. coli and Shigella, it’s one of several organisms in the Enterobacteriaceae family. Discovered by American scientist Daniel Elmer Salmon, it has been known to cause illness for over 125 years.
Salmonella stands out among pathogenic organisms for its high prevalence. The illness it causes, salmonellosis, is the most commonly reported cause of foodborne illness today.
The Salmonellagenus also contains more than 2,500 different serotypes – Salmonellaenterica being of greatest concern from a public health perspective. Collectively, these microorganisms have been associated with foods including raw meats, poultry, eggs, milk and dairy products, fish and seafood, spices (cocoa, chocolate) and numerous ready-to-eat items like sauces, salad dressings, cake mixes and cream-filled desserts.
Salmonella is widely dispersed in nature and can inhabit animals (many know it to be in pets like turtles and other reptiles) as well as humans, not to mention also being able to live in natural environments. It is known for contaminating pond-water sediment, irrigation water, soil, insects, factory equipment, hands and, at the consumer-level, kitchen surfaces and utensils.
Salmonella causes two forms of illness, which have a combined incidence rate of 15.2 sicknesses per 100,000 persons and result in an estimated 380 U.S. deaths per year on average. The first is gastrointestinal illness – vomiting, diarrhea, cramps and fever – with symptoms usually lasting a couple of days and tapering off within a week. These symptoms usually run their course in otherwise healthy persons within a week, but for immunocompromised individuals, Salmonella can spread to other organs and cause more severe illness. The U.S. Centers for Disease Control and Prevention (CDC) estimates that more than a million of these cases of salmonellosis occur annually in the U.S. and that there around 23,000 salmonella-induced hospitalizations, projections that factor in under-reporting and under-diagnosis.
The second illness, typhoidal illness, has many of the same symptoms but also a high fever, headache, lethargy and occasionally rashes. This condition – usually contracted from sewage‐contaminated drinking water or crops irrigated with sewage‐contaminated water rather than foods natively – is much more serious. According to the most recent estimates (published in 2014), approximately 21 million cases and 222,000 typhoid-related deaths occur annually worldwide. Each year in the US about 400 cases are reported and it is estimated that the disease occurs in about 6,000 people. The fatality rate, prior to use of antibiotics was 20% and with use of antibiotics and supportive care, mortality has been reduced to 1 to 2%.
Many salmonellosis cases stem from consumption of raw or undercooked poultry products, but fresh produce and low-moisture foods like spices also have been sources of major outbreaks in recent times.
Salmonella outbreaks can result in numerous hospitalizations. One outbreak of Salmonella Heidelberg associated with a chicken brand resulted in the hospitalization of over 600 individuals in 29 states and Puerto Rico. The poultry processor responsible recalled 40,000+ pounds of chicken products, a process that didn’t end until it was able to institute improved control measures to reduce contamination.
Many consumers know that Salmonella is hard to wash off from food. Cooking, hand washing, keeping raw foods separated from cooked foods, and maintaining proper refrigeration are all key to preventing it from spreading. Obviously, cross contamination may occur at any point in the “farm-to-fork” food process and from any contaminated source, whether that’s a food item or an infected handler, animal, surface contact or otherwise.
The U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS) oversees process controls for handling and microbiological monitoring of poultry and eggs (as well as meats) and is probably the regulatory agency with the greatest influence throughout the world for thwarting Salmonella. In 2016, FSIS issued new standards it expects will prevent 50,000 illnesses per year, and since that time foreign regulatory bodies have taken steps to harmonize their systems.
These global changes have reinforced the need for easier and more effectively managed Salmonella identification. While isolation and detection methods have long been developed for many foods with a history of Salmonella contamination, conventional methods involve collecting samples, streaking on to a growth medium and culturing, and typically require 4 to 6 days for to get results.