Salmonellosis is a symptomatic infection caused by bacteria of the genus Salmonella. It is one of the most common diseases to be known as food poisoning (though the name refers to food-borne illness in general). These are defined as diseases, usually either infectious or toxic in nature, caused by agents that enter the body through the ingestion of food. In humans, the most common symptoms are diarrhea, fever, abdominal cramps, and vomiting. Symptoms typically occur between 12 hours and 36 hours after exposure, and last from two to seven days. Occasionally more significant disease can result in dehydration. The old, young, and others with a weakened immune system are more likely to develop severe disease. Specific types of Salmonella can result in typhoid fever or paratyphoid fever. Typhoid fever and paratyphoid fever are specific types of salmonellosis, known collectively as enteric fever, and are, respectively, caused by salmonella typhi and paratyphi bacteria, which are only found in humans. Most commonly, salmonellosis cases arise from salmonella bacteria from animals, and chicken is a major source for these infections.
There are two species of Salmonella: Salmonella bongori and Salmonella enterica with many subspecies. However, subgroups and serovars within a species may be substantially different in their ability to cause disease. This suggests that epidemiologic classification of organisms at the subspecies level may improve management of Salmonella and similar pathogens.
Both vegetarian and non-vegetarian populations are susceptible to Salmonella infections. Infection is usually spread by consuming contaminated meat, eggs, water or milk, but other foods may spread the disease if they have come into contact with manure. Some pet animals, including cats, dogs, and reptiles, can also carry and spread the infection. Diagnosis is by a stool test or blood tests.
Procedures to prevent the disease include proper washing and preparation of food, and cooking to appropriate temperature. Mild disease typically does not require specific treatment. More significant cases may require treatment of electrolyte problems and intravenous fluid replacement. In those at high risk or in whom the disease has spread outside the intestines, antibiotics are recommended.
Salmonellosis is one of the most common causes of diarrhea globally. In 2015, 90,300 deaths were caused by nontyphoidal salmonellosis, and 178,000 by typhoidal salmonellosis. In the United States, about 1.35 million cases and 450 deaths occur from non-typhoidal salmonellosis a year. In Europe, it is the second most common foodborne disease after campylobacteriosis.
Signs and symptoms Enteritis
After a short incubation period of a few hours to one day, the bacteria multiply in the small intestine, causing an intestinal inflammation (enteritis). Most people with salmonellosis develop diarrhea, fever, vomiting, and abdominal cramps 12 to 72 hours after infection. Diarrhea is often watery and non-bloody but may be mucoid and bloody. In most cases, the illness lasts four to seven days, and does not require treatment. In some cases, though, the diarrhea may be so severe that the patient becomes dangerously dehydrated and must be hospitalized. At the hospital, the patient may receive fluids intravenously to treat the dehydration, and may be given medications to provide symptomatic relief, such as fever reduction. In severe cases, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites, and can cause death, unless the person is treated promptly with antibiotics.
In otherwise healthy adults, the symptoms can be mild. Normally, no sepsis occurs, but it can occur exceptionally as a complication in the immunocompromised. However, in people at risk such as infants, small children, and the elderly, Salmonella infections can become very serious, leading to complications. In infants, dehydration can cause a state of severe toxicity. Extraintestinal localizations are possible, especially Salmonella meningitis in children, osteitis, etc. Children with sickle-cell anemia who are infected with Salmonella may develop osteomyelitis. Treatment of osteomyelitis, in this case, will be to use fluoroquinolones (ciprofloxacin, levofloxacin, etc., and nalidixic acid).
Those whose only symptom is diarrhea usually completely recover, but their bowel habits may not return to normal for several months.
Typhoid fever
Typhoid fever occurs when Salmonella bacteria enter the lymphatic system and cause a systemic form of salmonellosis. Endotoxins first act on the vascular and nervous apparatus, resulting in increased permeability and decreased tone of the vessels, upset thermal regulation, vomiting, and diarrhea. In severe forms of the disease, enough liquid and electrolytes are lost to upset the fluid balance, cause an electrolyte imbalance, decrease the circulating blood volume and arterial pressure, and cause hypovolemic shock. Septic shock may also develop. Shock of mixed character (with signs of both hypovolemic and septic shock) are more common in severe salmonellosis. Oliguria and azotemia develop in severe cases as a result of renal involvement due to hypoxia and toxemia.
Long-term Salmonellosis is associated with later irritable bowel syndrome and inflammatory bowel disease (IBD). Evidence however does not support that salmonellosis directly causes IBD.
A small number of people afflicted with salmonellosis experience reactive arthritis, which can last months or years and can lead to chronic arthritis. In sickle-cell anemia, osteomyelitis due to Salmonella infection is much more common than in the general population. Though Salmonella infection is frequently the cause of osteomyelitis in people with sickle-cell, it is not the most common cause, which is Staphylococcus infection.
Those infected may become asymptomatic carriers, but this is relatively uncommon, with shedding observed in only 0.2 to 0.6% of cases after a year.
Causes
Contaminated food, often having no unusual look or smell Poor kitchen hygiene, especially problematic in institutional kitchens and restaurants because this can lead to a significant outbreak Excretions from either sick or infected but apparently clinically healthy people and animals (especially dangerous are caregivers and animals) Polluted surface water and standing water (such as in shower hoses or unused water dispensers) Unhygienically thawed poultry (the meltwater contains many bacteria) An association with reptiles (pet tortoises, snakes, iguanas, and aquatic turtles) is well described Amphibians such as frogs Rodents; in particular rats and mice Insects such as flies, ants and cockroaches
Salmonella bacteria can survive for some time without a host; they are frequently found in polluted water, with contamination from the excrement of carrier animals being particularly important.
The growing trend of keeping exotic animals as household pets has significantly increased the risk of direct Salmonella transmission to humans. A wide range of animals, including birds, reptiles, amphibians, domesticated animals, and rodents, can carry and spread Salmonella. These pets shed bacteria through their feces, which can lead to direct pet-to-human transmission of salmonellosis through contaminated surfaces, improper handling, or lack of hygiene. Raising awareness about safe pet handling practices, regular sanitation, and proper hygiene is essential to reduce the risk of infection.
The European Food Safety Authority highly recommends that when handling raw turkey meat, consumers and people involved in the food supply chain should pay attention to personal and food hygiene.
An estimated 142,000 Americans are infected each year with Salmonella Enteritidis from chicken eggs, and about 30 die. The shell of the egg may be contaminated with Salmonella by feces or environment, or its interior (yolk) may be contaminated by penetration of the bacteria through the porous shell or from a hen whose infected ovaries contaminate the egg during egg formation. Such interior egg yolk contamination is theoretically unlikely. Even under natural conditions, the rate of infection was very small (0.6% in a study of naturally contaminated eggs and 3.0% among artificially and heavily infected hens).
Prevention
The US Food and Drug Administration (FDA) has published guidelines to help reduce the chance of food-borne salmonellosis. Food must be cooked to , and liquids such as soups or gravies should be boiled when reheating. Freezing kills some Salmonella, but it is not sufficient to reliably reduce them below infectious levels. While Salmonella is usually heat-sensitive, it acquires heat-resistance in high-fat environments such as peanut butter. Salmonellosis can also be understood through a One Health approach, which recognizes that the health of people is closely connected to the health of animals and the shared environment. The World Health Organization notes that non-typhoidal Salmonella is widely distributed in food animals and pets and can pass through the food chain, so prevention depends on control measures from production to consumption as well as good hygiene after animal contact. Vaccine Antibodies against nontyphoidal Salmonella were first found in Malawi children in research published in 2008. The Malawian researchers identified an antibody that protects children against bacterial infections of the blood caused by nontyphoidal Salmonella. A study at Queen Elizabeth Hospital in Blantyre found that children up to two years old develop antibodies that aid in killing the bacteria. This could lead to a possible Salmonella vaccine for humans.
A 2014 study tested a vaccine on chickens which offered efficient protection against salmonellosis.
Vaccination of chickens against Salmonella essentially wiped out the disease in the United Kingdom. A similar approach was considered in the United States, but the Food and Drug Administration decided not to mandate vaccination of hens.
Treatment
Electrolytes may be replenished with oral rehydration supplements (typically containing salts sodium chloride and potassium chloride).
Appropriate antibiotics, such as ceftriaxone, may be given to kill the bacteria, but are not necessary in most cases. Azithromycin has been suggested to be better at treating typhoid in resistant populations than both fluoroquinolone drugs and ceftriaxone. There are recommendations on choice of antibiotic to avoid promoting antibiotic resistance.
There is no evidence of benefit of treating healthy people with diarrhea due to non-typhoidal salmonellosis. However, the evidence for the very young, very old or people with severe diseases are uncertain.
Epidemiology
United States
Salmonellosis annually causes, per CDC estimation, about 1.35 million illnesses, 26,500 hospitalizations, and 420 deaths in the United States every year. About 142,000 people in the United States are infected each year with Salmonella Enteritidis specifically from chicken eggs, and about 30 die.
In 2010, an analysis of death certificates in the United States identified a total of 1,316 Salmonella-related deaths from 1990 to 2006. These were predominantly among older adults and those who were immunocompromised. The U.S. government reported as many as 20% of all chickens were contaminated with Salmonella in the late 1990s, and 16.3% were contaminated in 2005.