Salmonella FAQ'S & Facts

What is salmonella?

Salmonella is a gram-negative rod-shaped bacteria that causes one of the most common intestinal infections in the United States – salmonellosis.  Salmonellosis is the second most common food borne illness in the United States (slightly less frequent than campylobacter infection).  The Center for Disease Control (CDC) estimates that approximately 1.4 million cases of salmonellosis occur yearly in the United States.  Of these, approximately 30,000 are culture confirmed cases (through blood, urine or stool cultures) reported to the CDC.  Approximately 600 deaths (roughly 30% of all foodborne related deaths) are caused by salmonella infections in the U.S. every year. 

The genus salmonella is subdivided into 50 serogroups (A, B, C1, C2, D, E, etc), which are further subdivided into over 2500 serotypes.  Approximately 2000 of these serotypes can cause human illness.

More than half of salmonellosis cases are caused by three serotypes: salmonella Enteriditis, salmonella Typhimurium, and salmonella Heidelberg.

How do people become infected with salmonella?

More than 95% of salmonella infections are transmitted by the consumption of foods contaminated with the bacteria.

Salmonella bacteria live in the intestinal tracts of many animals, including cattle and poultry, wild animals, and pets.  The bacterium is often found in these animals’ feces.  Salmonella are usually transmitted to humans who unknowingly consume food contaminated with the feces.  Food may also become contaminated when someone infected with salmonella handles or prepares food for someone else.

How can I tell if my food is contaminated with salmonella?

You can’t.  Foods contaminated with salmonella usually look, smell, and taste normal.  Contaminated food sources typically associated with salmonella are poultry, eggs, red meat, raw milk, and diary products.  More recently, infection has been associated with unpasteurized orange juice, cantaloupe, tomatoes, alfalfa sprouts, and other fresh produce.

What are the symptoms of a salmonella infection?

The infectious dose of salmonella is very small – often no more than 15-20 cells – which can multiply at an alarming rate.  Salmonella can cause three different types of illness: gastroenteritis, typhoid fever, and bacteremia.

Gastroenteritis is the most common clinical manifestation of salmonellosis, characterized by fever, diarrhea (sometimes bloody), and abdominal cramps within 6 to 72 hours after consumption of the contaminated product.  Other common symptoms include vomiting, urinary tract infections, dysuria, pain in urination, nausea, headaches, myalgia (muscle pain), arthralgia (joint pain), fatigue, and dehydration.  The illnesses usually last 5 to 7 days and most people recover without treatment, although some may require re-hydration with intravenous fluids. 

Severe gastroenteritis may require hospitalization.  In these patients, the salmonella infection can spread from the intestines to the blood stream and into other body sites.  Under these circumstances, the infection can cause death unless the patient is treated properly with antibiotics.  Infants, elderly people, and people with impaired immune systems are more likely than others to become severely ill. 

Typhoid fever, also known an enteric fever, is a rare illness caused by salmonella Typhi.  The onset of symptoms usually occurs within 5 to 21 days after ingestion of the salmonella Typhi bacteria.  Symptoms may include constipation, cough, sore throat, headache, and a rash on the individual’s chest, as well as the slowing of the heartbeat and enlargement of the liver and spleen.

Bacteremia is characterized by infection of tissues surrounding the brain and spinal cord (meningitis) and infection within the bloodstream (sepsis).  This condition occurs when salmonella bacteria enter and circulate within and individual’s bloodstream.

How is a salmonella infection detected?

A salmonella infection is usually diagnosed by a positive culture from a stool sample of the infected person.  In more severe illnesses, salmonella bacteria can sometimes be detected in a contaminated person’s blood or urine.  In most cases, doctors do not order a culture and simply treat the symptoms.  Even when a culture is ordered, detection of salmonella can be very difficult.  When examining each of these cultures, the laboratory technician is asked to pick out (under a microscope) salmonella bacteria from thousands of other bacteria which are normally present in the cultures.  In addition, cultures taken from people who have already started a course of antibiotics are less likely to produce positive results, even if those persons are infected with salmonella bacteria.  As a result, only about 3% of salmonella cases are officially detected and reported nationwide.

How is a salmonella outbreak detected?

The CDC explains that in order to find cases in an outbreak of salmonella infections, public health laboratories serotype the salmonella bacteria and perform a kind of “DNA fingerprinting” on laboratory samples. Investigators determine whether the “DNA fingerprint” pattern of salmonella bacteria from one patient is identical to those from other patients in the outbreak and from the contaminated food. Bacteria with the same “DNA fingerprint” are likely to come from the same source.

Once an outbreak (defined as two or more identical salmonella isolates) have been identified, public health officials then conduct intensive investigations, including interviews with ill people, to determine if people whose infecting bacteria match by “DNA fingerprinting” are part of a common source outbreak.

A series of events occurs between the time a patient is infected and the time public health officials can determine that the patient is part of an outbreak. This means that there will be a delay between the start of illness and confirmation that a patient is part of an outbreak.  The timeline is as follows:

1. Incubation time: The time from eating a contaminated food to the beginning of symptoms. For salmonella, this is typically 1-3 days, sometimes longer.
   
   
2. Time to contact with health care provider/doctor: The time from the first symptom until the person seeks medical care, when a diarrhea sample is collected for laboratory testing. This time may be additional 1-5 days, sometimes longer.
   
   
3. Time to diagnosis: The time from when a person gives a sample to when salmonella is obtained from it in a laboratory. This may be 1-3 days from the time the sample is received in the laboratory.
   
   
4. Sample shipping time: The time required to ship the salmonella bacteria from the laboratory to the state public health authorities that will perform serotyping and “DNA fingerprinting”. This usually takes 0-7 days depending on transportation arrangements within a state and the distance between the clinical laboratory and the public health department. It should be noted that the diagnostic laboratories are not required by law to forward salmonellaisolates to the public health labs and not all diagnostic laboratories forward any isolates unless specifically requested.
   
   
5. Time to serotyping and “DNA fingerprinting”: The time required for the state public health authorities to serotype and to perform “DNA fingerprinting” on the salmonellaand compare it with the outbreak pattern. Serotyping may take up to 3 days. The “DNA fingerprinting” can be accomplished in 2 working days (24 hours). However, many public health laboratories have limited staff and space, and experience multiple emergencies at the same time. Thus, this process may take 1-10 days for both serotyping and "DNA fingerprinting" together.

The time from the beginning of the patient’s illness to the confirmation that he or she was part of an outbreak is typically about 2-3 weeks. Case counts in the midst of an outbreak investigation are therefore always preliminary and must be interpreted within this context.

Are there any long term complications of a salmonella infection?

Persons with salmonellosis usually recover completely, although it may take several months before their bowel habits are entirely normal.  Recent studies have indicated that 25% of patients reported altered bowel habits six months after a bacterial gastroenteritis illness.

Unfortunately, some people develop two more serious complications: Irritable Bowel Syndrome (IBS) and Reiter’s Syndrome.

Irritable Bowel Syndrome

Irritable Bowel Syndrome is a functional bowel disorder characterized by abdominal pain and alternating bouts of diarrhea and constipation.  Other symptoms include whitish mucous in the stool, a feeling of incomplete evacuation (tenesmus), and bloating or abdominal distension. 

Researchers have identified several medical conditions, or comorbidities, which appear more frequently in patients diagnosed with IBS.  These include headaches, depression, fibromyalgia, inflammatory bowel disease, abdominal surgery, and endometriosis.  For most people, IBS is a chronic condition, although the severity of symptoms varies over time. 

IBS is commonly treated by attempting to relive its symptoms.  Doctors routinely suggest one or more of the following for IBS patients: fiber supplements, anti-diarrheal medications, elimination of high-gas foods, anticholinergic medications, antidepressant medications, and counseling.  

IBS can be extremely painful, embarrassing, costly,  and can dramatically affect one’s quality of life and productivity at work.  Recent studies indicate that IBS patients incur an average annual medical cost of $5,049 and $406 in out-pocket expenses.  In addition, a study of workers afflicted with IBS found that they reported a 34.6% loss in productivity, corresponding to 13.8 hours lost for a 40-hour work week.

Reiter’s Syndrome

Reiter’s Syndrome, which includes and is sometimes referred to as reactive arthritis, is an uncommon but debilitating result of a salmonella infection.  Reiter’s Syndrome is disorder that causes at least 2 of 3 seemingly unrelated symptoms: