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Salmonella

Salmonellosis is an acute infectious disease of humans and animals, caused by salmonella serovars and occurs in children more often in the form of gastrointestinal, less often - typhoid and septic forms.

Etiology. Salmonella are motile gram-negative bacteria that do not have capsules and do not form spores. The main Salmonella antigens are flagellated (H), cell wall antigens (O) and thermolabile envelope antigens (Vi) that block the agglutination reaction of O-antigens and O-antibodies. Allocate more than 2,200 Salmonella serotypes. The currently used nomenclature provides for the allocation of three groups of Salmonella: S. enteritidis, S. typhi and S. choleraesuis. Each type of Salmonella is divided into bio-types, for example S. enteritidis bio-thyphimurium.

Salmonella is resistant to many physical factors, die at a temperature of 54.4 ° C after 1 h, and at 60 ° C - after 15 min, remain viable in the environment at a reduced temperature for many days, for weeks they live in stagnant waters, dried food, pharmacological agents and faeces.

The properties of Salmonella, which determine their pathogenicity, remain unclear. Endotoxin increases the resistance of the microorganism to phagocytosis, therefore, strains with a deficiency of this antigen are usually avirulent. The action of endotoxin on the macroorganism is manifested in general disorders, although not playing an important role in the development of gastroenteritis. Some types of Salmonella affect mostly humans, causing characteristic symptoms of the disease. Infection with S. typhosa is observed only in humans, salmonella groups A and C are mainly detected in humans, and S. alrortus equi - only in horses.

Epidemiology. Human infection occurs when consuming contaminated food or water. The main carrier of salmonella is a person, often serving as a source of food contamination and poisoning. Breast milk can also be a source of salmonella spread. So, some strains of this pathogen were isolated from milk and feces of donors. A patient in the acute period of infection with 100 g of salmonella is released from 1 g of feces.

Their excretion with feces continues for 2 weeks after infection in 70-90% of patients, in 50% it lasts up to 4 weeks and in 10-25% - up to 10 weeks.

The duration of the period of a bacteriocarrier is the same in symptomatic and asymptomatic forms, but in children under 1 year of age it is longer than in older children. The periods of bacterial carriers are increasing during treatment with antibiotics.

Pathogenesis and pathology. The dose of the pathogen necessary for the development of the disease in humans is not precisely established. For both adults and children, it is determined by the body's resistance and the virulence of the pathogen.

Salmonella indirectly stimulates the energy system of intestinal epithelial cells, resulting in increased secretion of water and electrolytes. The diarrhea-causing Salmonella strains contribute to the appearance of neutrophilic cellular infiltration in its own membrane. Prostaglandins released from inflammatory exudates can also stimulate the adenylate cyclase system, enhancing the secretion of fluid and electrolytes.

For the development of enterocolitis requires the presence of Salmonella in the depths of the intestinal mucosa. The contents of the stomach with a pH of 2.0 kills pathogens, whereas higher values ​​have a different effect on Salmonella. At pH 5.0 or more, the pathogens remain viable. Accelerated passage of food through the intestines, lysozyme and other enzymes can also resist Salmonella infection.

Salmonella overcomes the surface layers of the intestinal mucosa, without damaging epithelial cells. Around them are concentrated phagosomes that do not have a noticeable effect on microorganisms that penetrate through cells or into the knitting membrane. Serotypes that cause diarrhea cause leukocyte infiltration of the basement membrane. The infection does not spread further, and the patient has only diarrhea, sometimes the body temperature rises slightly. The incidence of bacteremia is unknown, but it is usually transient, metastatic foci of infection in healthy children are usually not formed.

Systemic diseases caused by salmonella are found mainly in the elderly and in patients with severe impaired cellular immunity and function of the reticuloendothelial system.
Salmonella septicemia and osteomyelitis often develop in children suffering from sickle cell anemia. Granulomatous diseases in children or other dysfunction of leukocytes increase the susceptibility to infection. Chronic Salmonella bacteremia and bacteriuria occur in patients with schistosomiasis, also characterized by imperfect phagocytosis.

Clinical manifestations. Gastroenteritis is most often seen in late summer and early fall, which coincides with an increase in the frequency of food infections. Large epidemics occur at this particular time, but sporadic cases occur throughout the year. The incubation period is 8-48 hours. Symptoms often appear in the morning after taking contaminated food the night before. The onset is acute, accompanied by nausea, vomiting, cramping abdominal pains, after which a large amount of feces of liquid consistency, sometimes with admixture of mucus and blood, departs. Vomiting is usually abundant and short-lived. Body temperature rises to 38–39 ° C in 70% of patients, but chills are less common. Lethal outcomes are rare (about 1%), mainly in individuals from the high-risk group.

Infection in some individuals proceeds without an increase in body temperature with minor disorders of bowel function. In other patients, the body temperature rises sharply, headaches appear, consciousness is disturbed, convulsions and meningeal phenomena develop. Sometimes there is a strong abdominal distension, muscle tension, significant local pain.

Hematogenous dispersion of salmonella is accompanied by chills and fever. It is usually observed in children under 3 months. Sometimes the symptoms may resemble a picture of typhoid fever, but it is not so long and rarely leads to death. Salmonella can settle in any organ, causing pneumonia, abscesses, empyema, osteomyelitis, purulent arthritis, pyelonephritis or meningitis.

Complications. Non-typhoid salmonellosis usually occurs without complications or is limited to extraintestinal manifestations. In rare cases, children have reactive arthritis, developing 2 weeks after the onset of diarrhea, Reiter’s disease (conjunctivitis, urethritis, polyarthritis).

The diagnosis is made on the basis of the obtained results of bacteriological studies, when the material is incubated on a medium enriched with tetrathionate followed by subculture on a selective medium. A preliminary result can be obtained using the method of direct fluorescence of antibodies; microscopic examination of urine, blood, feces, wall brain fluid (CSF) and other affected organs; serological tests to help diagnose typhoid and other salmonellosis.

Differential diagnosis. Salmonella gastroenteritis must be differentiated from other viral and bacterial diseases accompanied by diarrhea, including those caused by rotaviruses, intestinal sticks, Yersinia and Campylobacter. Sometimes clinical data and radiographic signs suggest ulcerative colitis, which should be excluded.

Treatment. Treatment should be directed at correcting electrolyte disturbances and maintaining adequate hydration. Treatment with antibiotics is indicated only in some cases: with the risk of spreading the infection (up to 3 months old, with an immunodeficient condition or a severe progressive course of the disease).

With septicemia, high body temperature and metastatic foci of infection, children should be treated with ampicillin, amoxicillin or chloramphenicol, one of which is prescribed in 4 doses with an interval of 6 hours. The choice of antibiotic is determined by the sensitivity of the pathogen.

The prognosis for salmonella gastroenteritis is usually favorable, with the exception of very young children and patients with severe comorbidity. With salmonella endocarditis and meningitis, it is unfavorable even with early and intensive care.

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Salmonella

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