Information for Healthcare Professionals and Laboratories

All About Salmonella with Dr. Ian Plumb

Consultant epidemiologist Dr. Ian Plumb

Listen as CDC medical epidemiologist Dr. Ian Plumb discusses Salmonella infection in this five-part podcast series from Consultant360external icon. Topics include symptoms, diagnostic tests, treatment options, patient follow-up, and closing knowledge gaps.

Estimates

CDC estimates that approximately 1.35 million illnesses and 420 deaths occur due to non-typhoidal Salmonella annually in the United States1.

Incidence

FoodNet reports that the annual incidence of Salmonella infection in the United States was 15.2 illnesses per 100,000 individuals2.

Trends

Compared to 2010-2012, the incidence of non-typhoidal Salmonella infection showed a 9% decrease in 20132. Visit the FoodNet website for more detailed information about the most recent trends in Salmonella infection.

Risk Factors

  • Salmonella infection is more common in the summer months (June, July, and August) than winter.
  • Children under 5 years old are the most likely to get a Salmonella infection3.
  • Infants who are not breast fed are more likely to get a Salmonella infection4.
  • Children who are 5 years old and younger, adults over 65 years old, and people with weakened immune systems are the most likely to have severe infections.
  • Certain medications (for example, medications to reduce stomach acid) can increase the risk of Salmonella infection5.

Outbreaks

In 2012, 831 foodborne outbreaks were reported to CDC6. They were caused by a variety of pathogens, and 106 of them were confirmed Salmonella. Salmonella accounted for the most hospitalizations (64%) in outbreaks with a confirmed cause6. In the largest recent outbreak, between March 2013 and July 2014, over 600 individuals in 29 states and Puerto Rico were infected with seven outbreak strains of Salmonella Heidelberg7. This outbreak was associated with one brand of chicken, that led to a company recall of over 40,000 pounds of chicken products8, and ended after the company instituted new control measures to reduce contamination.

Salmonella was discovered more than a century ago. Salmonellosis, the illness caused by Salmonella, primarily results in a mild to severe diarrheal illness, known as acute gastroenteritis.

Symptoms

Symptoms of acute gastroenteritis due to infection with Salmonella can include9:

Key terms:

Enteric: an infection of the gastrointestinal tract

Extra-intestinal: an infection occurring outside the intestine

Gastroenteritis: inflammation of the stomach and large and small intestines that may result in vomiting or diarrhea

Invasive infection: an infection of the bloodstream, bone, joint, brain, or nervous system

  • Sudden onset of diarrhea (which may be bloody)
  • Abdominal cramps
  • Fever (almost always present)
  • Nausea, vomiting, and headache may occur, though less frequent

Diarrhea may last for several days and lead to potentially severe dehydration, especially in infants and children under 2 years old and in adults over 65 years old. Even after clinical symptoms are no longer obvious, Salmonella bacteria may be found in the stool for several weeks.

Most people with diarrhea due to a Salmonella infection recover completely, although it may be several months before their bowel habits are entirely normal.

Sometimes, Salmonella infection can spread to urine, blood, bones, joints, the brain, or the nervous system, causing symptoms related to that body part or system. Some of these extra-intestinal infections can have long-term effects, depending on which part of the body is infected.

Invasive Salmonella Infections

When Salmonella infections become invasive, they can affect the bloodstream, bone, joint, brain, or nervous system, or other internal organs.

Invasive Salmonella infections:

  • Can be severe and potentially life-threatening.
  • Occur in about 8 percent of persons with laboratory-confirmed Salmonella infection.10
  • May occur as:
    • Bacteremia (infection of the blood)
    • Meningitis (infection of the membranes lining the brain and spinal cord)
    • Osteomyelitis (infection of the bone)
    • Septic arthritis (infection of a joint).
  • Are rarely fatal, but most commonly occur in people who are very young or old or have a weakened immune system.

How is Salmonella infection treated?

Giving fluids is very important. Oral fluids are usually sufficient, but people with severe diarrhea may require intravenous (IV) fluids. Most people do not require antibiotics.

Should Salmonella infections be treated with antibiotics?

Petri dish of Salmonella

Antibiotics are NOT recommended for treating most patients with Salmonella infection.

Antibiotics are recommended for

  • Patients with HIV infection.
  • Other immunocompromised patients (e.g., organ transplant recipients; those receiving corticosteroids or other immunosuppressive agents;  those with cancer or lymphoproliferative disease with current or recent chemotherapy; and those with sickle cell disease, hemoglobinopathies, or disorders of the reticuloendothelial system, including cirrhosis).
  • Patients older than age 50 with cardiac, valvular, or endovascular abnormalities, or substantial joint disease.
  • People who have severe illness, such as severe diarrhea (nine to ten stools per day), high or persistent fever, or a condition requiring hospitalization.
  • Adults age 65 or older.

In healthy people with Salmonella infection, antibiotics generally do not shorten the duration of illness, diarrhea, or fever. The main risks of treatment include adverse effects of the antibiotic, the possibility of prolonged asymptomatic Salmonella carriage, and disturbance of the microbiome. Unnecessary antibiotic use also contributes to antibiotic resistance.

CDC tracks Salmonella infections that are resistant to antibiotics through NARMS, the National Antimicrobial Resistance Monitoring System.

The germs that contaminate food can be resistant because of the use of antibiotics in people and in food animals. We can prevent many of these infections with careful antibiotic use and by keeping Salmonella out of the food we eat.

What should I know about treating patients with resistant Salmonella infections?

If Salmonella bacteria are resistant, first-choice antibiotics recommended to treat these infections might not work. Healthcare providers might need to prescribe second- or third-choice drugs, but these might be less effective, administered through an IV instead of orally, more toxic, and more expensive. Recommended antibiotics for severe infections include fluoroquinolones, azithromycin, and third generation cephalosporins.

How does CDC track resistant Salmonella infections?

CDC tracks these infections through the National Antimicrobial Resistance Monitoring System (NARMS). The NARMS program at CDC helps protect public health by providing information about emerging bacterial resistance, the ways in which resistance is spread, and how resistant infections differ from susceptible infections.

Learn more about resistant Salmonella with these resources from NARMS.

Phenotype: an organism’s physical traits 

Serotype: groups in a single species of microorganisms, such as bacteria or viruses, which share distinctive surface chemical structures

The genus Salmonella is a member of the family Enterobacteriaceae. Like other Enterobacteriaceae, Salmonellae are Gram-negative, rod-shaped bacilli. The genus Salmonella can be divided into two species (S. enterica and S. bongori), based on their phenotypic profile. S. enterica can be further divided into six subspecies using their phenotypic profile.

The most common serotypes of Salmonella that cause human infection are Enteritidis, Typhimurium, Newport, and Javiana. These Salmonella serotypes account for about half of culture-confirmed Salmonella isolates reported by public health laboratories12.

Typhoidal and Nontyphoidal Salmonella

Salmonella bacteria are classified as either “typhoidal” or “nontyphoidal,” based on their serotype.

  • Typhoidal Salmonella refers to the specific Salmonella serotypes which cause typhoid fever or paratyphoid fever, including Typhi, Paratyphi A, Paratyphi B (see note below), and Paratyphi C.
    • Serotype Paratyphi B is tartrate-negative (unable to ferment tartrate) and causes typhoidal disease. Serotype Paratyphi B var. L(+)tartrate+  is tartrate-positive (able to ferment tartrate) and causes nontyphoidal disease.
  • Nontyphoidal Salmonella refers to all other Salmonella serotypes13.

How do People Get Salmonella?

Salmonella live in the intestinal tracts of humans and animals. You can get Salmonella infection from a variety of sources, including:

  • Eating contaminated food or drinking contaminated water.
  • Touching infected animals and not washing your hands afterwards.

Contaminated Food or Water

Did You Know?

A person who is in close contact with, or in an area where animals live and roam, can get germs on their hands— even if they do not directly touch an animal.

Salmonella is usually transmitted to humans by eating foods contaminated with small amounts of animal feces. Contaminated foods usually look and smell normal. They are often foods of animal origin, such as beef, poultry, milk, fish, or eggs, but any food, including vegetables and fruit or processed foods, may become contaminated.

Foods can also be contaminated in the kitchen. Drippings from raw meat or poultry can contaminate surfaces and other foods in the refrigerator or shopping cart. When raw meat or poultry are prepared with a cutting board and knife without being washed thoroughly between uses, they can contaminate other foods.

When preparing raw meat or poultry, food handlers can transfer Salmonella on their hands to other foods if they do not wash their hands between food preparation steps. Food handlers who do not wash their hands with soap after using the bathroom can also contaminate food with Salmonella.

Contact with Infected Animals

Salmonella live in the intestinal tracts of humans and other animals, including poultry and other birds, amphibians, and reptiles. Salmonella may be found in the feces of some animals, and people can become infected if they do not wash their hands after contact with animals or animal feces.

Many animals can carry Salmonella germs but appear perfectly healthy and clean. Animals’ bodies, whether covered with fur, feathers, or scales, can be contaminated with germs. Reptiles, such as turtles, lizards, and snakes, are particularly likely to harbor Salmonella. Many chicks, ducks, and other poultry including those in backyard flocks can carry Salmonella in their feces. You cannot look at an animal and tell if it is infected with Salmonella.

The area where an animal lives, such as its cage or water in its tank or the places where an animal roams, may be contaminated with Salmonella, which can cause illness in people who come into direct contact with the animal area, cage, or tank water. Learn more about CDC’s Healthy Pets Healthy People initiative.

An Atlas of Salmonella in the United States, 1968-2011 pdf icon[PDF – 248 pages] summarizes 42 years of surveillance data on laboratory-confirmed Salmonella isolates from humans. The Atlas includes:

  • Analyses by age, sex, geography, and season
  • Reports of Salmonella isolates from animals and related sources (e.g., environment and feeds)

This is the first time CDC has posted these data online in a downloadable format. You can download the report in its entirety or in 32 individual Salmonella serotype reports.

For more information:

CDC has several surveillance systems for obtaining information about Salmonella. They serve different purposes and provide information on various features of the organism’s epidemiology, such as number of outbreaks, antimicrobial-resistant infections, and subtypes.

National Salmonella Surveillance Overview

National Salmonella surveillance is conducted through public health laboratories for culture-confirmed cases and through the National Notifiable Diseases Surveillance System (NNDSS). Active laboratory- and population-based surveillance is conducted in FoodNet sites. Learn more about Salmonella surveillance pdf icon[PDF – 12 pages].

Data:

Foodborne Disease Outbreak Surveillance System (FDOSS) captures data on pathogenic agents, foods, and settings responsible for outbreaks.

Website:

Data:

Foodborne Disease Active Surveillance Network (FoodNet) reports trends in foodborne infections and tracks the impact of food safety policies.

Website:

Data:

 

Laboratory-based Enteric Disease Surveillance (LEDS) collects information on Salmonella isolates causing human infection, including serotyping to help assess geographic differences and long term trends

Website:

  • Laboratory-based Enteric Disease Surveillance (LEDS)
  • Enteric Diseases Laboratory Branch (EDLB)

Data:

National Antimicrobial Resistance Monitoring System—Enteric Bacteria (NARMS) monitors and reports antimicrobial resistance in enteric bacteria, including Salmonella, from human, retail meats, and animals

Website:

Data:

National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet) connects cases of illness nationwide to quickly identify outbreaks, including many that would otherwise go undetected.

Website:

Data:

National Notifiable Diseases Surveillance System (NNDSS) tracks notifiable diseases across the United States.

Website:

Data:

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References
  1. CDC. Antibiotic Resistance Threats in the United States, 2019. Atlanta, GA: U.S. Department of Health and Human Services, CDC; 2019.
  2. CDC. Incidence and Trends of Infection with Pathogens Transmitted Commonly Through Food — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2006–2013. MMWR Morb Mortal Wkly Rep. 2014;63(15);328-332
  3. CDC. Foodborne Diseases Active Surveillance Network (FoodNet): FoodNet Surveillance Report for 2012 (Final Report) pdf icon[PDF – 53 pages]. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC. 2014.
  4. Jones TF, et al. A case-control study of the epidemiology of sporadic Salmonella infection in infantsexternal icon. Pediatrics. 2006; 118(6): 2380-2387.
  5. Bavishi C, DuPont HL. Systematic Review: The use of proton pump inhibitors and increased susceptibility to enteric infectionexternal icon. Alimentary Pharmacology & Therapeutics. 2011; 34(11-12): 1269-1281.
  6. CDC. Surveillance for Foodborne Disease Outbreaks, United States, 2012, Annual Report pdf icon[PDF – 20 pages]. Atlanta, Georgia: US Department of Health and Human Services, CDC, 2014.
  7. CDC.  Multistate Outbreak of Multidrug-Resistant Salmonella Heidelberg Infections Linked to Foster Farms Brand Chicken. 2014.
  8. FSIS.  California Wholesale Store Recalls Rotisserie Chicken Products Due to Possible Salmonella Heidelberg Contaminationexternal icon. 2013.
  9. American Public Health Association. Control of Communicable Diseases Manual 19th edition, An Official Report of the American Public Health Association.  19th edition. 2008.
  10. CDC, National Salmonella Surveillance Data, unpublished, 2013
  11. Centers for Disease Control and Prevention (CDC). Antibiotic Resistant Threats in the United States, 2015. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC, 2015.
  12. CDC. Foodborne Diseases Active Surveillance Network (FoodNet): FoodNet Surveillance Report for 2012 (Final Report) pdf icon[PDF – 36 pages]. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC. 2014.
  13. Reactive arthritis after enteric infections in the United States: the problem of definition. Townes JM. Clin Infect Dis. 2010 Jan 15;50(2):247-54.