Procalcitonin in Differentiating Enteric Fever from Salmonellosis and Antibiotic Recommendations
Procalcitonin (PCT) is a valuable biomarker for differentiating enteric fever from non-typhoidal salmonellosis, with higher levels (>2 ng/mL) strongly suggesting enteric fever or invasive salmonellosis requiring immediate antibiotic therapy, while lower levels may indicate non-invasive salmonellosis that often doesn't require antibiotics.
PCT as a Diagnostic Marker
PCT levels rise within 2-3 hours of bacterial infection onset, with higher levels correlating with infection severity (0.6-2.0 ng/mL for SIRS, 2-10 ng/mL for severe sepsis, >10 ng/mL for septic shock) 1
PCT has higher specificity (93%) than C-reactive protein (CRP) for distinguishing bacterial from viral infections, making it more useful in differentiating invasive salmonellosis from viral gastroenteritis 2
Extremely elevated PCT levels (>10 ng/mL) strongly suggest serious bacterial infection with sepsis, as seen in cases of severe intestinal infections like enteric fever 3
A PCT value ≥1 μg/L has better specificity, sensitivity, and predictive value than CRP, interleukin-6, and interferon-alpha for distinguishing between viral and bacterial infections 2
Differentiating Enteric Fever from Non-typhoidal Salmonellosis
Enteric fever (typhoid/paratyphoid) typically presents with high PCT levels due to its invasive nature and bacteremia, while non-invasive salmonellosis may show lower PCT values 4
PCT levels <0.4 ng/mL can help rule out bacteremia, which is a key feature of enteric fever but not typically present in uncomplicated salmonellosis 4
In a study of febrile patients, PCT levels were significantly higher in patients with bacteremia than in those without (11.9 ± 25.1 vs. 2.5 ± 14.7 ng/mL), supporting its use in identifying invasive infections like enteric fever 4
PCT should be used as part of a systematic evaluation that includes clinical examination and directed diagnostic techniques, not as a standalone test 5
Diagnostic Approach
Blood cultures remain the gold standard for diagnosis of enteric fever, with a sensitivity of approximately 50% compared to bone marrow culture (which has higher sensitivity) 5
Culture-independent diagnostic testing, including panel-based multiplex molecular diagnostics from stool and blood specimens, should be performed when there is clinical suspicion of enteric fever or diarrhea with bacteremia 5
Additional cultures of bone marrow, stool, duodenal fluid, and urine may be beneficial to detect enteric fever, particularly if antimicrobial agents have been administered prior to testing 5
Serologic tests should not be used to diagnose enteric fever due to poor performance characteristics 5
Antibiotic Recommendations
People with clinical features of sepsis who are suspected of having enteric fever should be treated empirically with broad-spectrum antimicrobial therapy after blood, stool, and urine culture collection 5
For enteric fever, fluoroquinolones have been effective: norfloxacin, pefloxacin, and ofloxacin 400 mg twice daily for 7-14 days or ciprofloxacin 500 mg twice daily for 10 days 6
For non-typhoidal Salmonella infections, particularly those caused by STEC (Shiga toxin-producing E. coli), antimicrobial therapy should be avoided, especially for STEC O157 and other STEC that produce Shiga toxin 2 5
Empiric therapy should attempt to provide antimicrobial activity against the most likely pathogens based upon each patient's presenting illness and local patterns of infection 5
Monitoring and De-escalation
Daily reassessment of antimicrobial regimen is recommended for potential de-escalation to prevent the development of resistance, reduce toxicity, and reduce costs 5
PCT can be used to support shortening the duration of antimicrobial therapy in sepsis patients and to support the discontinuation of empiric antibiotics in patients who initially appeared to have sepsis but subsequently have limited clinical evidence of infection 5
Serial PCT measurements may be more valuable than a single reading, particularly in post-surgical patients 1
Important Considerations and Pitfalls
PCT levels alone cannot differentiate sepsis from other causes of SIRS; they should be part of a systematic evaluation that includes clinical examination and directed diagnostic techniques 5
Do not delay empiric antibiotic therapy in critically ill patients while awaiting PCT results if bacterial infection is clinically suspected 1
Remember that PCT can be elevated in non-infectious conditions including shock states and drug reactions 1
Immunocompromised patients may present with atypical manifestations of salmonellosis, including multifocal osteomyelitis and pulmonary involvement, requiring a high index of suspicion 7