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
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