Salmonella Workup
Obtain stool culture for Salmonella (along with Shigella, Campylobacter, Yersinia, C. difficile, and STEC) in patients with fever, bloody or mucoid stools, severe abdominal cramping, or signs of sepsis 1.
Clinical Indications for Testing
Stool Testing
Perform stool culture when patients present with:
- Fever with diarrhea
- Bloody or mucoid stools
- Severe abdominal cramping or tenderness
- Signs of sepsis
These features indicate potential bacterial pathogens requiring antimicrobial therapy 1.
A single stool specimen is sufficient - multiple specimens do not increase diagnostic yield 1.
Blood Cultures
Blood cultures are mandatory in the following scenarios 1:
- Infants <3 months of age (regardless of presentation)
- Any age with signs of septicemia
- Suspected enteric fever (typhoid/paratyphoid)
- Systemic manifestations of infection
- Immunocompromised patients
- High-risk conditions (hemolytic anemia, sickle cell disease)
- Travel history to enteric fever-endemic areas with unexplained fever
Critical technical point: Collect 2-3 blood cultures of 20 mL each in adults to maximize detection, as bacteremia magnitude is low (0.3-1.0 CFU/mL). Draw blood before administering antibiotics 1.
Special Considerations for Enteric Fever
When to Suspect Typhoid/Paratyphoid
Consider enteric fever in febrile patients (with or without diarrhea) who have 1:
- Travel to endemic areas (South/Southeast Asia, Central/South America, Africa)
- Consumed food prepared by recent travelers from endemic regions
- Laboratory exposure to Salmonella Typhi or Paratyphi
Key clinical distinction: Diarrhea is uncommon in enteric fever - patients typically present with fever, headache, lethargy, malaise, abdominal pain, and hepatosplenomegaly 1.
Diagnostic Approach for Enteric Fever
- Blood culture (sensitivity ~50%) is the practical first-line test 1
- Bone marrow culture (more sensitive but invasive) - particularly valuable if antibiotics already given 1
- Additional cultures: stool, duodenal fluid, urine may be helpful 1
- Do NOT use serologic tests - poor performance characteristics 1
Additional Workup Components
Assess for Dehydration
All patients with acute diarrhea require evaluation for dehydration, which significantly increases mortality risk, especially in young children and elderly 1.
Screen for Extraintestinal Complications
Evaluate for postinfectious and extraintestinal manifestations 1, particularly:
- Vascular infections (mycotic aneurysms, especially in elderly with atherosclerosis)
- Endocarditis (particularly with pre-existing heart disease)
- Septic arthritis, osteomyelitis
- Soft tissue infections (in patients with vascular disease or skin breakdown)
Recent case reports demonstrate that invasive Salmonella can occur even in immunocompetent individuals 2, 3, 4, though this remains uncommon.
Common Pitfalls to Avoid
- Don't order blood cultures in uncomplicated gastroenteritis - reserve for high-risk patients and those meeting criteria above
- Don't use serology for enteric fever diagnosis - unreliable 1
- Don't collect multiple stool specimens - single sample is adequate 1
- Don't delay blood cultures - collect before antibiotics to maximize sensitivity 1
- Don't assume only gastroenteritis - maintain suspicion for invasive disease in elderly, immunocompromised, or those with persistent fever despite treatment
Immunocompromised Patients
Broader differential diagnosis required with consideration of additional pathogens beyond standard bacterial panel 1. Blood cultures should be obtained from immunocompromised patients who are febrile or have positive stool bacterial pathogens 1.