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. 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. TRANSMISSION 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. PATHOPHYSIOLOGY 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. SALMONELLOSIS 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. MORTALITY & MORBIDITY 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. TYPHOID FEVER 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. FREQUENCY 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. PRECIPITATING FACTORS 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). DIFFERENTIAL DIAGNOSES Cryptosporidiosis Campylobacter infection Cyclospora Listeria monocytogenes Escherichia Coli infection Shigellosis LAB FINDINGS 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. leukopenia is typical but WBC may be normal. Widal test is not diagnostic, titer > 1:320 or 4 fold increase in titer support the diagnosis. CLINICAL PICTURE 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). CLINICAL PICTURE/2 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. CLINICAL PICTURE/3 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. LOCAL COMPLICATIONS Intestinal hemorrhage Intestinal perforation Paralytic ileus Zenker degeneration of abdominal muscles SYSTEMIC COMPLICATIONS Endocarditis Arteritis & arterial emboli Cholecystitis Hepatic & splenic abscesses Pneumonia or empyema Osteomyelitis & septic arthritis Meningitis Urinary tract infection TREATMENT 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. NURSING CARE 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. PREVENTION 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. PROGNOSIS 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.
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