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Sleuthing Salmonella – Removing the Mystery of One of America’s Most Common Food Bugs

Posted in Outbreaks & Recalls,Salmonella on June 23, 2018

There have been 10 national Salmonella outbreaks this year, and that’s not even counting any localized ones. From eggs to sprouts, from chickens to chicken salad, Salmonella has snuck its way into a variety of things we eat … and touch. If you have heard about the outbreaks related to Honey Smacks and pre-cut melon recently, you may find yourself wondering about this food poisoning predator.

Despite how common Salmonella is (it is among the most common foodborne pathogen in the United States), many people still are not sure what exactly it is.

Well, hang onto your notebooks. Our Salmonella sleuthing is giving you the clue to debunking the mystery that is this bacterium. 

Salmonella: What is it?

The bacterium Salmonella is a one-celled microorganism commonly known for its role in foodborne illness and impacts on the gastrointestinal tract.  Salmonella can be found in the intestinal tract of humans and animals, on certain animals such as turtles and chickens, and in the environment.  Statistically, these infections are more prevalent in the warmer months of Summer than the colder months of Winter.

The effects of Salmonella have a large impact even though the organism is so small that you can’t see it with your own eyes.  This is why we call it a microorganism.  Specialized equipment is needed to glimpse these busy bacteria.  Under a microscope you can see its long, rounded shape and little flagella (tiny hair like legs that allow it to move about).  Salmonella is a rod shaped, gram negative bacterium from the family of Enterobacteriaceae and gets its name from the American scientists attributed to its discovery.  Dr. Daniel E. Salmon (a veterinarian) along with Theobald Smith, MD discovered this bacterium in 1885.

While there are many types of Salmonella bacteria, Salmonella serotype Typhimurium and Salmonella serotype Enteritidis are the most common serotypes found in the United States.  A serotype is a group of microorganisms within a single species that share a specific surface chemical structure.  Chemically, they look and behave differently from other bacteria that fall into different serotypes.  These serotypes further break down Salmonella species into closer and more specific family groups.  While most Salmonella serotypes behave the same in the infected host, this information allows scientists to discern one from another.  Serotyping an infected person and/or contaminated food product allows investigators to link a source to an illness as well as link those who are sick with the same illness.  This genetic serotype testing allows epidemiologists to trace outbreaks to identify a source so that a recall can help prevent others from falling ill.  Serotyping is a great tool in the public health sector.

The Numbers: How Common is Salmonella Infection?

The statistics for Salmonellosis, the illness associated with Salmonella infections, are quite startling.  Even more so are the breakdowns of where people get sick and how they become infected.  Salmonellosis is responsible for about 1.2 million illnesses in the United States each year according to the Center for Disease Control and Prevention (CDC).  The accounts for 23,000 hospitalizations and 450 deaths.

Of the 1.2 million Salmonella illnesses, 1.1 million are acquired in the United States, the other 0.1 million acquire abroad and return to the United States.  According to the CDC, most of the Salmonella illness acquired in the United States is a result of foodborne illness.  Foodborne Salmonella infection results in about 19,000 hospitalizations and around 380 deaths each year.

Higher Risk: Who is More Susceptible to Infection?

While anyone can become infected if exposed to Salmonella, some groups of the population are at a higher risk for infection.  Children, more specifically children under the age of 5 years are at a statistically higher risk for infection compared to other age groups.  The very young, the very old, and those with a compromised or weakened immune system are at the highest risk for severe infections.  Those is these higher risk categories should take extra precaution to avoid contamination and illness.

Symptoms: What Can I Expect If I Am Infected?

Initial symptoms of Salmonella infection often begin within 12 to 72 hours after exposure and can last for as long as 4 to 7 days depending on severity and personal factors.  Symptoms include fever, diarrhea, and abdominal cramps.  In most cases, individuals can recover without treatment, allowing the infection to run its course and pass.  In some cases, however, patients may experience severe diarrhea that causes extreme dehydration and require hospitalization.  In other extreme cases, the bacteria may spread from the intestinal tract to the blood stream or other parts of the body.  When this occurs, prompt antibiotic treatment is necessary to prevent fatality.  The very young, the very old and those with a compromised or weakened immune system are more likely to experience serious illness associated with Salmonella infection and also account for a higher mortality rate associated with this illness.

Additional Symptoms: What are the Long-Term Consequences to Salmonella Infection?

Most individuals with diarrheal illness associated with Salmonella infection recover completely.  Even though the seriousness and illness will pass quickly, it may be several months before bathroom activity fully resumes fully to normality.

But for some, the effects are long lasting.  A small number of people may develop a condition known as reactive arthritis.  This presents as joint pain after diarrheal symptoms have subsided but may commonly include irritation of the eyes and even painful urination.  Reactive arthritis symptoms may persist for several months up to years and can lead to chronic arthritis.  This painful reaction does not seem more or less likely based on whether the patient receives antibiotic treatment.

Diagnosis: How Do I Know I Have Salmonella?

Many illnesses cause some of the same symptoms as Salmonellosis.  Symptoms of fever, abdominal cramps, and diarrhea are not exclusive to this illness and require targeted testing to identify the pathogen.  To be sure of a Salmonella diagnosis, a clinical laboratory will need to test your sample.  This sample can be performed on a stool or blood sample, depending on the diagnostic requirements of the laboratory or requesting health care professional instructions.

Initially, the sample will be screened for the potential bacteria your healthcare professional suspects to be the cause of illness.  This can include one or more microorganisms of interest.  Initial testing is often performed by culturing the sample.  This method involves taking a small amount of the specimen and placing it on a growth medium.  Growth medium contains a set of food and conditions suitable for specific bacteria to grow.  Different bacteria grow on different growth mediums, allowing the laboratory technician to “culture confirm” the presence of a particular bacteria.

Once Salmonella has been identified, additional characterization testing, such as serotyping can be performed to better identify a potential source.  Additionally, DNA fingerprinting can be performed for epidemiological purposes.  DNA fingerprinting involves a specialized molecular test in which DNA sequencing is performed on the sample.  This data is uploaded by the testing laboratory (at the state and territorial level of public health laboratories) to the CDC’s Laboratory-bases Enteric Disease Surveillance and to PulseNet.  PulseNet is a network that allows epidemiologists to track and link illness and discover trends and outbreaks.  Public health laboratories can also send samples that present atypical serotypes or unique results to the CDC’s National Salmonela Reference Laboratory.  Here additional characterization or confirmation may be performed.

Antibiotic Resistance: Why Are Some Infections Harder to Treat?

Many infections resolve without any medical intervention.  Under these conditions, the affected individual treats the symptoms of dehydration and allows the illness to run its course.  For some, antibiotic treatment is a necessity.  Unfortunately, in these cases the illness is so severe that proper treatment must be administered to avoid fatal complications.

To treat salmonellosis and other gastrointestinal infections, only a few common use and limited range antibiotics are considered for treatment.  The overuse of these antibiotics or relative prevalence of these antibiotics has led to the emergence of Salmonella strains who are resistant to antibiotics.  In other words, one or more specific antibiotics do not kill the pathogenic bacteria.

Antibiotic resistance occurs when the bacteria evolve in response to its environment.  When exposed to antibiotics, most of the bacteria will die.  If not enough antibiotic is administered or some of the bacteria are just different enough to not be fully killed by the antibiotic.  This is the birth of antibiotic resistant bacteria.  These bacteria produce a defense mechanism making it resistant to the antibiotic effects of the medication.

This type of infection is more difficult to treat.  It often involves a trial and error to identify that the antibiotics are not working.  When the patient does not respond to the medication, it is generally due to antibiotic resistant infection.  In some cases, a health care professional will request a sensitivity test to determine the best antibiotic to use for that particular patient.

Sensitivity tests use samples from the infected individual to identify which medication the bacteria of interest will respond to.  This response factor is determined by using growth mediums laced with individual antibiotics.  If the antibiotic growth medium does not generate bacterial growth, it is likely that particular antibiotic will be effective against the infection.  If antibiotic growth medium does generate bacterial growth, the strain involved is resistant to that particular antibiotic.

Many Salmonella enterica have acquired antibiotic resistance genes over time.  This indicates that these bacteria commonly infecting humans has discovered ways to adapt to survive within human hosts.  Salmonella is not the first bacteria to demonstrate antibiotic resistance.  Antibiotic resistance has been around for almost as long as antibiotics have been around.  Just four years after mass production and use of the common antibiotic penicillin, the first antibiotic resistant bacteria were isolated and identified.

Quick Tips: How Can I Prevent Salmonella Infection?

There is no Salmonella vaccine at this time, so best approach to Salmonellosis is prevention.  Keep in mind a few simple tips and approaches to prevent the spread of Salmonella infection.  Cleanliness, safe food handling and storage, and smart practices with high risk individuals are prevention tactics used to avoid infection with Salmonella and other harmful bacteria.


The most important step in preventing infection is cleanliness.  Handwashing is high on the cleanliness list.  Be sure to wash your hands before and after handling food with soap and hot water.  Also wash hands when transitioning from one food item to another and certainly between raw and ready-to-eat foods.  Wash kitchen work surfaces, cutting boards, and utensils immediately after they have come in contact with raw meat or raw poultry.

Foodborne contamination is just one area that we take in harmful bacteria.  We come in contact with Salmonella and other potentially harmful bacteria in other aspects of our daily lives.  Wash your hands often and especially after touching frequently touched surfaces or environmental surfaces.  Additional vigilance should be exercised when handling animals.  Wash hands with soap and hot water after handling baby chicks, birds, reptiles, and after contact with pet feces.

Salmonella can also be found in the intestines of certain animals, including chicks and ducklings.  Feces from these animals contaminates their living environments and transfers to the surface of the animal.  Small children, the very old, and those with a compromised immune system should not handle poultry animals and should wash their hands after contact with them.  Cuddling and kissing the birds is strongly discouraged due to the increased risk of illness.

Food Handling and Storage

Store cooked foods and raw foods separately to avoid cross-contamination.  Cook ground beef (160 ⁰F), poultry (165 ⁰F), and eggs (160 ⁰F) thoroughly.  If you are served undercooked meat, poultry, or eggs at a restaurant do not hesitate to send it back to the kitchen.  Your health and safety is worth the wait.  Do not eat or drink foods that contain raw eggs or raw or unpasteurized milk.  These products may contain harmful bacteria.

People who have salmonellosis should avoid food serving and preparing food or drinks for others until diarrheal symptoms have resolved.  In some cases, local health departments will require restaurant workers to demonstrate a negative stool test prior to returning to work to ensure the illness cannot spread to unsuspecting patrons.

Smart Practices with High Risk Individuals

Those falling into the “high risk individuals” category include the very young, the very old, and those with a compromised immune system.  Extra caution should be maintained when preparing foods for those within these groups.  Do not work with raw poultry or meat and care for an infant at the same time.  Situations may include feeding or changing diapers while preparing a meal.  Contact between high risk individuals and reptiles such as snakes, turtles, iguanas, and other lizards should be avoided.  This includes both direct contact (holding or petting the reptile) and indirect contact (touching surfaces in reptile enclosures and/or contact with someone who has touched a reptile that has not sufficiently cleaned up).

By: Heather Van Tassell, Contributing Writer (Non-Lawyer)