Salmonella infection
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SALMONELLA INFECTION Abdelaziz Elamin, MD, PhD, FRCPCH College of Medicine Sultan Qaboos University INTRODUCTION Discovered in 1880 & named after Daniel Salmon, the pathologist who first isolated the organism from porcine intestine.

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Abdelaziz Elamin, MD, PhD, FRCPCH

College of Medicine

Sultan Qaboos University

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  • Discovered in 1880 & named after Daniel Salmon, the pathologist who first isolated the organism from porcine intestine.

  • Salmonella is a motile, gram-negative, rod-shaped bacteria, which is a leading cause of bacterial food-borne diseases.

  • Of the 2000 strains recognized, human infection are caused mainly by 5 serotypes, typhi, paratyphi, typhimurium, choleraesuis & enteritidis.

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  • Infection follows ingestion of contaminated food or water. Meat, poultry, eggs & diary products are frequent sources.

  • Pets, domestic animals and infected human are potential reservoirs. Person to person & animal to human transmission is recognized.

  • In healthy humans a dose of about one million bacteria is necessary to produce symptoms.

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After ingestion salmonella must survive the stomach acidic PH & colonize small intestine.

Salmonella then attach to & penetrate the gut mucosa resulting in diarrhea from direct mucosal damage & by action of exotoxins.

Another portal of entry is invasion of lymphoid tissue in the GIT (peyer patches) & multiplication within macrophages leading to bacteremia.

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  • Salmonella typically produces 3 distinct syndromes: food poisoning, typhoid fever & asymptomatic carrier state.

  • Salmonella gastroenteritis manifest as vomiting & diarrhea within 6-48 hours after ingestion of food or drink contaminated with bacteria.

  • It is self-limiting, treatment is by water & salts replacement. Antibiotics are not usually needed.

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  • Infection with nontyphoidal salmonella produces self-limiting gastroenteritis and food poisoning.

  • Whereas mortality caused by typhoid fever is rare in western countries, it is associated with significant mortality & morbidity in tropical countries (10-30%).

  • Dehydration is the most common complication of typhoid fever, but serious intestinal & extra-intestinal complications may occur.

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  • Typhoid fever is the most serious salmonella infection with significant morbidity & mortality.

  • Caused by salmonella typhi & paratyphi.

  • Incubation period is 1-2 weeks.

  • Salmonella has somatic (O antigen) & flagellar H antigen. The O antigen is more specific for serologic testing.

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  • An estimated 15-30 million cases of typhoid fever occur globally each year.

  • The disease is endemic in many developing countries in Asia, Central America & Africa.

  • Outbreak of typhoid fever have been reported recently from Eastern Europe.

  • Incidence in Sudan is not exactly known, but estimated as 50 per 100,000 people/year.

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  • Defects in cellular-mediated immunity (AIDS, Transplant patients & malignancy).

  • Defects in phagocytic function (malaria, histoplasmosis & schistosomiasis).

  • Splenectomy or functional asplenia (sickle cell dis)

  • Low stomach PH ( patients on anti-ulcer drug).

  • Prolonged use of antibiotics (altered gut flora).

  • Injured gut barrier (bowel disease or surgery).

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Campylobacter infection


  • Listeria monocytogenes

  • Escherichia Coli infection

  • Shigellosis

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  • Salmonella can be grown from blood or bone marrow in the 1st week, from stool in the 2nd week & from urine in the 3rd week.

  • Special media are needed for transport & for culture.

  • leukopeniais typical but WBC may be normal.

  • Widal test is not diagnostic, titer > 1:320 or 4 fold increase in titer support the diagnosis.

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  • Symptoms begin with sudden onset of high-grade fever, headache & dry cough.

  • Fever is swinging or may show step ladder pattern & patient initially feel well & mobile.

  • Abdominal pain & toxicity follow soon & by the end of 1st week spleen is palpable & pink, discrete, skin rash appears over the trunk.

  • Constipation is more common than diarrhea which is usually greenish in color (pea soup).

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  • Abdominal tenderness & hepatomegaly occur in 50% of patients.

  • The pulse is relatively slow in relation to fever (Paget sign).

  • The tongue is coated with free margins & halitosis may be present.

  • The sweat of some patients smell like yeast.

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  • The 3rd week of illness is the usual time for complications in the untreated patients.

  • Local gut as well as systemic complications may occur.

  • Serious infections may progress rapidly to drowsiness & coma which is usually fatal (coma vigil).

  • Mortality is unlikely after the 4th week & patients may become carrier if not treated.

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  • Intestinal hemorrhage

  • Intestinal perforation

  • Paralytic ileus

  • Zenker degeneration of abdominal muscles

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  • Endocarditis

  • Arteritis & arterial emboli

  • Cholecystitis

  • Hepatic & splenic abscesses

  • Pneumonia or empyema

  • Osteomyelitis & septic arthritis

  • Meningitis

  • Urinary tract infection

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  • Medical care include rehydration, antipyretics & antibiotics.

  • Drugs of choice are Ceftriaxone & ciprofloxacin but Cotrimoxazole & Chloramphenicol are still used in developing countries. Ampicillin kills bacilli hiding in the bile & hence prevents or reduce the carrier state.

  • Chronic resistant carrier state may necessitate cholecystectomy. Surgical care may also be needed in patients with intestinal complications.

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  • Isolation & barrier nursing is indicated

  • Notification of the case to the infection control nurse in the hospital.

  • Trace source of infection.

  • continue breastfeeding infants & young children and give ORS & light diet for other patients in the first 48 hours.

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  • Education on hygiene practices like hand washing after toilet use & avoidance of eating in non hygienic restaurants.

  • Proper handling & refrigeration of food even after cooking.

  • Salmonella TAB vaccine is available but affectivity is low (50% claimed protection).

  • Antibiotic prophylaxis is not needed for house-hold contacts.

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  • With early diagnosis and prompt treatment most patients with typhoid fever will recover in due time.

  • Fever & toxicity subsides within 72 hours of antibiotic treatment.

  • Mortality is > 50% in untreated severe typhoid fever particularly in children & elderly.

  • Recrudescence is rare but chronic carrier state is reported in 10% of patients.