Current Antibiotic Susceptibility of Salmonella Typhi in India
Based on the most recent evidence, Salmonella Typhi in India shows high resistance to fluoroquinolones, with re-emergence of susceptibility to first-line antibiotics (chloramphenicol, ampicillin, cotrimoxazole), and continued susceptibility to third-generation cephalosporins and azithromycin, though increasing MICs for azithromycin are concerning.
Current Susceptibility Pattern
First-line Antibiotics
- Chloramphenicol: 94.9-97.8% susceptibility 1, 2
- Ampicillin/Amoxicillin: 77.2-97.8% susceptibility 1, 2
- Cotrimoxazole: 75.9-97.8% susceptibility 1, 2
Fluoroquinolones
- Ciprofloxacin: Only 32.9-40.9% susceptibility 1
- Nalidixic acid: High resistance (76.6-100%) 3, 2
- Ofloxacin/Levofloxacin: 89.1-91.3% intermediate or resistant 2
Current Treatment Options
Evolution of Resistance Patterns
The resistance pattern of S. Typhi in India has evolved significantly:
1990s: Multiple drug-resistant (MDR) strains emerged with resistance to chloramphenicol, trimethoprim, and ampicillin 4
2000s-2010s: Notable decline in MDR strains with re-emergence of susceptibility to first-line antibiotics 3
Current trend: High resistance to fluoroquinolones with decreasing ciprofloxacin susceptibility 3, 2
Regional Considerations
India shows higher rates of fluoroquinolone resistance in enteric pathogens compared to other regions 5. This is particularly important as fluoroquinolones were previously the mainstay of treatment for typhoid fever.
Treatment Implications
First-line Treatment
Based on current guidelines and susceptibility patterns:
- Ceftriaxone is the preferred first-line agent for patients returning from Asia, including India 5
- Azithromycin is a suitable oral alternative for uncomplicated disease 5
Alternative Options
- Re-emergence of susceptibility to traditional first-line drugs (chloramphenicol, ampicillin, cotrimoxazole) offers additional treatment options 3, 6
Important Clinical Considerations
Susceptibility testing is crucial: When testing isolates for antibiotic sensitivity, ciprofloxacin disc testing alone is unreliable. The isolate should also be tested for nalidixic acid susceptibility 5
Treatment duration: To reduce risk of relapse, treatment should be continued for 14 days 5
Monitoring for resistance: Emerging resistance to azithromycin and increasing MICs warrant careful monitoring 2, 6
Complications risk: Gastrointestinal bleeding, intestinal perforation, and typhoid encephalopathy occur in 10-15% of patients, especially if illness duration exceeds 2 weeks 5
Diagnostic Approach
- Blood cultures have highest yield within first week of symptoms (40-80% sensitivity)
- Stool and urine cultures become positive after the first week
- Widal test lacks sensitivity and specificity and is not recommended 5
The antibiotic susceptibility pattern of S. Typhi in India continues to evolve, requiring ongoing surveillance and judicious use of antibiotics to prevent further resistance development.