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. • leukopeniais 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.