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Salmonella Poisoning

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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What is Salmonella?

Salmonella (S.) is the genus name for a large number (over 2,500) of types of bacteria. Each type is distinctly identifiable by its specific protein coating. The types are otherwise closely related. Salmonella bacteria are rod-shaped, flagellated, Gram stain-negative, and are known to cause disease in humans, animals, and birds (especially poultry) worldwide. The two major diseases caused by Salmonella spp. are gastroenteritis and typhoid fever (typhoid and paratyphoid fevers) in humans.

The terminology that identifies the particular protein coats, or serovars, is not well settled, and what previously were thought to be various species of the genus Salmonella are now thought to be serovars of only two species, S. enterica and S. bongori, by many researchers. However, these designations are not always accepted in the scientific literature. and so common serovars that have been named in the past are still used (for example, S. typhi, S. typhimurium, S. paratyphi, S. enteritidis, S. cholerasuis, S. saintpaul). Minor variations in some serovars are termed subspecies and assigned a number. The serovars are identified by the Kauffman-White classification that uses two major types of antigens (somatic O, along with envelope antigens that may mask O antigens, and flagellar or H antigens) to distinguish the over 2,500 types of Salmonella bacteria. Sometimes laboratories or other reporting agencies identify isolates simply as Salmonella spp. (species) and do not identify the serovars. Nomenclature of these closely related bacteria is likely to remain in flux, even in the current literature.

The bacteria were first isolated by Theobald Smith in 1885 from pigs. The genus name Salmonella was derived from the last name of D.E. Salmon, who was Smith's director. In 1896, diagnosis of Salmonella spp. infection in humans was accomplished.

What are Salmonella poisoning symptoms?

Salmonellosis (gastroenteritis characterized by nausea, vomiting, and diarrhea) is the most common disease caused by the organisms. Abdominal cramping also may occur. Salmonellosis thus produces the symptoms that are commonly referred to as food poisoning. Although food poisoning is usually a mild disease, the nausea, vomiting, and diarrhea can lead to dehydration and even death (about 500 per year in the U.S.). It is important to note that many other organisms (for example, viruses, E. coli, Shigella) and toxins (for example, botulism, mushroom toxin, or pesticides) can produce food poisoning symptoms. However, over 1.4 million cases of salmonellosis occur per year in the U.S., and the rest of industrialized countries have similar high rates. Countries with poor sanitation have a much higher incidence of salmonellosis. Unfortunately, the above symptoms can occur with many types of infectious organisms such as Shigella, Staphylococcus, Campylobacter, some additional bacteria, viruses, and protozoa.

Typhoid fever occurs when some of the Salmonella organisms (often identified as Salmonella typhi or S. typhi) are not killed by the normal human immune defenses (macrophage cells) after they enter the gastrointestinal tract. Salmonella then survive and grow in the human spleen, liver, and other organs and may reach the blood (bacteremia). Salmonella can be shed from the liver to the gallbladder, where they can continue to survive and be secreted into the patient's feces for up to a year. Symptoms of typhoid include high fevers up to 104 F, sweating, inflammation of the stomach and intestines, and diarrhea. Symptoms usually resolve, but many patients become Salmonella carriers. Approximately half of patients develop slow heartbeat (bradycardia), and about 30% of patients get flat, slightly raised red or rose-colored spots on the chest and abdomen. Typhoid fever is also referred to as enteric fever.

Paratyphoid fever, like typhoid fever, is also termed enteric fever. Paratyphoid fever has symptoms like typhoid, but it's usually not as severe. Subtypes are A, B, and C and vary by having small changes in symptoms, such as more rose spots (A), gastroenteritis in conjunction with herpes labialis and gastroenteritis (B), rarely, with septicemia and abscesses (C). S. paratyphi is the organism that causes this disease.