Salmonellosis¶
Chapter 171 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Salmonella infections range from self-limiting gastroenteritis to life-threatening systemic disease (typhoid fever).
- Typhoid fever is caused by S. Typhi/S. Paratyphi, while nontyphoidal Salmonella (NTS) causes gastroenteritis and invasive infections.
- Antibiotic resistance is widespread, with DSC (ciprofloxacin-resistant) and MDR strains increasingly common.
- Vaccination (Ty21a, Vi CPS, TCV) and food/water safety measures are critical for prevention.
- Invasive NTS disease is a major cause of bacteremia in sub-Saharan Africa and HIV-positive individuals.
1. DEFINITION & OVERVIEW¶
Salmonellosis is a bacterial infection caused by Salmonella species, leading to gastroenteritis, typhoid fever, and invasive infections. Salmonella is a gram-negative bacillus with two species: S. enterica (pathogenic to humans) and S. bongori (non-pathogenic).
Table 171-1: Antibiotic Therapy for Enteric Fever in Adults¶
| INDICATION | AGENT | DOSAGE (ROUTE) | DURATION, DAYS |
|---|---|---|---|
| Empirical Treatment | Ceftriaxonea | 2 g/d (IV) | 10–14 |
| Ciprofloxacinb | 500 mg bid (PO) or 400 mg q12h (IV) | 5–7 | |
| Azithromycinc | 1 g/d (PO) | 5 | |
| Fully Susceptible | Ceftriaxone | 2 g/d (IV) | 10–14 |
| Ciprofloxacin | 500 mg bid (PO) or 400 mg q12h (IV) | 5–7 | |
| Azithromycin | 1 g/d (PO) | 5 | |
| Alternative treatment | Amoxicillin | 1 g tid (PO) or 2 g q6h (IV) | 14 |
| Chloramphenicol | 25 mg/kg tid (PO or IV) | 14–21 | |
| Trimethoprim-sulfamethox azole | 160/800 mg bid (PO) | 7–14 | |
| Multidrug-Resistant | Ceftriaxone | 2 g/d (IV) | 10–14 |
| Azithromycin | 1 g/d (PO) | 5 | |
| Ceftriaxone-Resistant | Meropenemd | 1 g q8h (IV) | 10–14 |
| Azithromycin | 1 g/d (PO) | 5 |
| INDICATION | AGENT | DOSAGE (ROUTE) | DURATION, DAYS |
|---|---|---|---|
| Eradication of Carriage | Ciprofloxacin | 500–750 mg bid (PO) | 28 |
| Azithromycin | 500 mg (PO) | 28 |
1.1 Taxonomy¶
Salmonella enterica subspecies I includes most human-pathogenic serotypes. Over 2,600 serotypes exist, with S. Typhi and S. Paratyphi causing typhoid fever. Nontyphoidal Salmonella (NTS) includes serotypes like Typhimurium and Enteritidis.
1.2 Transmission¶
Contaminated food/water (especially eggs, meat, produce), animal contact, and person-to-person spread. NTS is zoonotic, while typhoidal Salmonella is human-specific.
2. EPIDEMIOLOGY¶
Global burden: ~93–150 million NTS infections annually, ~60,000–155,000 deaths. Typhoid fever affects 11–21 million annually, with 10–30% mortality if untreated. High incidence in South Asia, sub-Saharan Africa, and Southeast Asia.
Table 171-2: Antibiotic Therapy for Nontyphoidal Salmonella Infection in Adults¶
| INDICATION | AGENT | DOSAGE (ROUTE) | DURATION, DAYS |
|---|---|---|---|
| Preemptive Treatmenta | Ciprofloxacinb | 500 mg bid (PO) | 2–3 |
| Severe Gastroenteritisc | Ciprofloxacin | 500 mg bid (PO) or 400 mg q12h (IV) | 7 |
| Azithromycin | 500 mg once daily | 5 | |
| Trimethoprim-sulfamethox azole | 160/800 mg bid (PO) | 7 | |
| Amoxicillin | 1 g tid (PO) | 7 | |
| Ceftriaxone | 1–2 g/d (IV) | 7 | |
| Bacteremia | Ceftriaxoned | 2 g/d (IV) | 7–14 |
| Ciprofloxacin | 400 mg q12h (IV), then 500 mg bid (PO) | ||
| Endocarditis or Arteritis | Ceftriaxone | 2 g/d (IV) | 42 |
| Ciprofloxacin | 400 mg q8h (IV), then 750 mg bid (PO) | ||
| Ampicillin | 2 g q4h (IV) | ||
| Meningitis | Ceftriaxone | 2 g q12h (IV) | 14–25 |
| Ampicillin | 2 g q4h (IV) | ||
| Other Localized Infection | Ceftriaxone | 2 g/d (IV) | 14–28 |
| Ciprofloxacin | 500 mg bid (PO) or 400 mg q12h (IV) | ||
| Ampicillin | 2 g q6h (IV) |
2.1 Demographics¶
Typhoid fever peaks in children <10 years and adults >40 years. NTS infections are more common in elderly, infants, and immunocompromised (e.g., HIV, sickle cell disease).
2.2 Risk Factors¶
Poor sanitation, contaminated food/water, travel to endemic regions, contact with infected animals, and immunosuppression.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Salmonella invades the intestinal mucosa via M cells, triggering endocytosis and intracellular survival. Typhoidal strains (S. Typhi) cause systemic infection, while NTS cause localized gastroenteritis or invasive disease.
3.1 Virulence Factors¶
Type III secretion systems, flagella, LPS, and efflux pumps. S. Typhi produces a toxin that disrupts host cell signaling.
3.2 Host Immune Response¶
Innate immune response (macrophage phagocytosis) and adaptive immunity (T-cell mediated). Immunocompromised patients are at higher risk for invasive disease.
4. CLINICAL FEATURES¶
Gastroenteritis: fever, abdominal pain, diarrhea. Typhoid fever: prolonged fever, relative bradycardia, rose spots. Invasive NTS: bacteremia, abscesses, endocarditis.
4.1 Typhoid Fever¶
Classic presentation: fever (38.8–40.5°C), abdominal pain, rose spots. Complications: intestinal perforation, septic shock.
4.2 Nontyphoidal Salmonellosis¶
Acute gastroenteritis (self-limiting) or invasive disease (bacteremia, abscesses). Risk factors: malnutrition, immunosuppression.
5. DIFFERENTIAL DIAGNOSIS¶
Malaria, viral hepatitis, dengue, leptospirosis, and other bacterial infections (e.g., Shigella, Campylobacter). Typhoid fever must be differentiated from typhus and viral gastroenteritis.
6. INVESTIGATIONS & DIAGNOSIS¶
Stool/blood cultures, serotyping, PCR, and molecular diagnostics. Blood cultures are most sensitive for typhoid fever (40–60%), while stool cultures are less reliable.
6.1 Diagnostic Criteria¶
Positive blood culture for S. Typhi/S. Paratyphi. Serology (Typhidot, Tubex) has limited accuracy. PCR detects bacterial DNA in blood.
6.2 Imaging¶
CT for abscesses, echocardiography for endocarditis, and MRI for osteomyelitis.
7. MANAGEMENT & TREATMENT¶
Antibiotics for invasive disease; supportive care for gastroenteritis. Treatment duration varies by infection type and resistance patterns.
Table 171-1: Antibiotic Therapy for Enteric Fever in Adults¶
| INDICATION | AGENT | DOSAGE (ROUTE) | DURATION, DAYS |
|---|---|---|---|
| Empirical Treatment | Ceftriaxonea | 2 g/d (IV) | 10–14 |
| Ciprofloxacinb | 500 mg bid (PO) or 400 mg q12h (IV) | 5–7 | |
| Azithromycinc | 1 g/d (PO) | 5 | |
| Fully Susceptible | Ceftriaxone | 2 g/d (IV) | 10–14 |
| Ciprofloxacin | 500 mg bid (PO) or 400 mg q12h (IV) | 5–7 | |
| Azithromycin | 1 g/d (PO) | 5 | |
| Alternative treatment | Amoxicillin | 1 g tid (PO) or 2 g q6h (IV) | 14 |
| Chloramphenicol | 25 mg/kg tid (PO or IV) | 14–21 | |
| Trimethoprim-sulfamethox azole | 160/800 mg bid (PO) | 7–14 | |
| Multidrug-Resistant | Ceftriaxone | 2 g/d (IV) | 10–14 |
| Azithromycin | 1 g/d (PO) | 5 | |
| Ceftriaxone-Resistant | Meropenemd | 1 g q8h (IV) | 10–14 |
| Azithromycin | 1 g/d (PO) | 5 | |
| Eradication of Carriage | Ciprofloxacin | 500–750 mg bid (PO) | 28 |
| Azithromycin | 500 mg (PO) | 28 |
7.1 Typhoid Fever¶
Ceftriaxone, ciprofloxacin, or azithromycin. Duration: 10–14 days. Corticosteroids may reduce mortality in severe cases.
7.2 Nontyphoidal Salmonellosis¶
Avoid routine antibiotics for uncomplicated gastroenteritis. Use ciprofloxacin, azithromycin, or TMP-SMX for invasive disease.
8. PROGNOSIS & COMPLICATIONS¶
Mortality: 2.5% overall, up to 30% without treatment. Complications include intestinal perforation, septic shock, abscesses, and endocarditis.
8.1 Long-term Outcomes¶
Chronic carriage in 2–5% of patients. Gallbladder cancer risk in S. Typhi carriers.
8.2 Special Populations¶
Higher mortality in elderly, immunocompromised, and those with underlying conditions (e.g., sickle cell disease).
9. SPECIAL CONSIDERATIONS¶
Vaccination (Ty21a, Vi CPS, TCV) for travelers and high-risk groups. Avoid high-risk foods in endemic areas. Monitor for antibiotic resistance in treatment decisions.
9.1 Pregnancy & Pediatrics¶
Avoid fluoroquinolones in children. Use ceftriaxone or azithromycin. Neonates require prolonged therapy.
9.2 Immunocompromised Patients¶
Higher risk of invasive disease. Consider prolonged antibiotic courses and surgical intervention for abscesses.
10. KEY POINTS & CLINICAL PEARLS¶
- Typhoid fever requires blood cultures and prompt antibiotic therapy.
- NTS gastroenteritis is self-limiting; avoid routine antibiotics.
- Use TCV in high-risk regions.
- Monitor for antibiotic resistance patterns in treatment decisions.