Salmonella Typhi

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.

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.

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).

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.

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.

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 2^nd week & from urine in the 3^rd 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.

Typhoid fever Laboratory diagnosis.

· Polymerase Chain Reaction (PCR)

· Culture of blood or bone marrow

· 80% during first week

· Culture of urine or stool

· in presence of characteristic clinical picture

· Serology test

· antibody test against somatic (O) or flagellar (H) antigen

Rapid test for typhoid fever.

· 80% sensitivity compared with blood culture

· PPV (92%) and NPV (64%) somewhat lower than that of culture

· Same day result

· Easy to perform

· High stability of components

DIPSTICK FOR DETECT IGM ANTIBODIES.

· Simple and rapid

· Required no equipment

· Highly stable reagents

· Low cost

· Easy to applied in field

What is S.typhi ?

· A bacteria

· Causes typhoid fever that affects 16 million people annually and causes 600,000 fatalities

· Has evolved the ability to spread from the intestine to the deeper tissues of humans, including the liver, spleen, and bone marrow

· Resistant to many drugs

· Closely related to Salmonella typhimurium (also already sequenced), classified under the same species as Salmonella typhi

· Difference is that S. typhi causes typhoid fever and can only infect humans, whereas S. typhimurium causes food poisoning and can affect almost all animals

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).

· 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.

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.