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Salmonella Infection

BASICS

  • Definition: Infection with any serotype of Salmonella (gram-negative, facultatively anaerobic bacilli).
  • Clinical syndromes:
  • Nontyphoidal gastroenteritis (most common, foodborne)
  • Enteric fever (see “Typhoid Fever”)
  • Chronic carrier state (>1 year)
  • Invasive disease: bacteremia, endovascular infections, focal abscess, osteomyelitis
  • At risk: Elderly (>65), infants (<3 mo), immunocompromised (HIV, malignancy), hemoglobinopathies (e.g., sickle cell).

EPIDEMIOLOGY

  • Incidence:
  • Global: ~94 million nontyphoidal cases/year
  • US: 1.4 million cases/year, 25,000 hospitalizations, 420 deaths/year
  • Peak frequency: July–November
  • Second most common bacterial cause of diarrhea in US (after Campylobacter)

ETIOLOGY & PATHOPHYSIOLOGY

  • Species: Salmonella enterica (2,500+ serotypes)
  • Transmission: ~95% foodborne (undercooked eggs, meat, dairy, produce; contact with reptiles/poultry/human carrier)
  • Infection process: Invades ileal/colonic mucosa → inflammation; can enter lymphatics/bloodstream → systemic disease

RISK FACTORS

  • Recent travel (underdeveloped nations)
  • Consumption of undercooked/contaminated food or unpasteurized dairy
  • Contact with reptiles, poultry, or human carriers
  • Gastric acid suppression (PPIs, H2 blockers, achlorhydria)
  • Recent antibiotics
  • Hemoglobinopathies (sickle cell), malaria, immunosuppression, chronic granulomatous disease, extremes of age

PREVENTION

  • Food safety (cook food thoroughly, refrigerate, hand hygiene)
  • Avoid contact with high-risk animals/feces
  • CDC tracks outbreaks: CDC Salmonella

COMMONLY ASSOCIATED CONDITIONS

  • Gastroenteritis
  • Bacteremia
  • Osteomyelitis (especially in sickle cell)
  • Abscesses (more common with malignancy)
  • Reactive arthritis

DIAGNOSIS

History

  • Asymptomatic or mild, self-limited gastroenteritis
  • Exposure: food/travel/animal contacts
  • Onset: 8–72 hr after ingestion; resolves in 4–10 days
  • Symptoms: sudden diarrhea (occasionally bloody in children), fever, cramps, headache, myalgias, rarely vomiting

Physical Exam

  • Fever, signs of dehydration, abdominal tenderness
  • +/- Heme-positive stool, hepatosplenomegaly

Differential

  • Viral gastroenteritis
  • Other bacterial enteritis (Shigella, E. coli, Campylobacter)
  • Pseudomembranous colitis
  • IBD

Diagnostic Tests

  • Stool culture (indications: severe diarrhea, >1 wk, fever, blood/mucus, outbreak)
  • Blood cultures if <3 mo, septicemia/systemic illness, enteric fever, immunocompromised
  • Other cultures: CSF in infants, wound/abscess cultures as needed
  • Imaging: As indicated for focal infections (CT/MRI)
  • Carrier state: Stool cultures >1 year; urine culture possible
  • Labs: Fecal leukocytes, nonspecific
  • Note: Asymptomatic fecal excretion can persist weeks; follow-up cultures usually not needed unless public health concern.

TREATMENT

General Measures

  • Supportive care: Hydration, electrolyte replacement, barrier precautions in hospital
  • Avoid antimotility agents if fever/dysentery present

Medications

  • Uncomplicated gastroenteritis: Supportive only; NO antibiotics in most healthy patients (can prolong carrier state)
  • Antibiotics indicated in:
    • Severe diarrhea/high fever/hospitalization
    • Infants <3 mo, elderly >50 (esp. >65), immunocompromised, hemoglobinopathy, prosthetic devices
    • Invasive/focal disease (bacteremia, abscess)
    • Chronic carriage

Adults

  • Levofloxacin 500 mg PO qd x 1–3 days
  • Ciprofloxacin 500–750 mg PO qd x 1–3 days
  • Azithromycin 500 mg PO qd x 3 days
  • Complicated/bacteremia: fluoroquinolone + ceftriaxone 1–2 g IV qd x 10–14 days

Children

  • Ceftriaxone 100 mg/kg/day IV/IM divided BID x 7–10 days
  • Azithromycin 20 mg/kg PO x1, then 10 mg/kg PO qd x 6 days

Carrier state

  • Amoxicillin 1 g PO TID x 12 wks, or
  • TMP-SMX 160/800 mg PO BID x 12 wks, or
  • Ciprofloxacin 500 mg PO BID x 4 wks (or other fluoroquinolone)
  • Adjust based on susceptibilities

Localized infection

  • Drain abscesses; treat with ≥3 wks antibiotics

ALERT

  • Increasing resistance to ampicillin, chloramphenicol, TMP-SMX, and fluoroquinolones
  • Multidrug-resistant strains common in reptiles (esp. pet reptiles)
  • Aztreonam is alternative for unusual resistance/multiple allergies

SURGERY

  • Drainage of infected sites; cholecystectomy for chronic carriage with gallstones

ONGOING CARE

  • Monitoring: Routine follow-up for complicated/invasive infections
  • Carrier state: Some require clearance cultures, esp. food handlers/health workers (local regulation)

DIET

  • Easily digestible foods

PATIENT EDUCATION

  • Hand hygiene, food safety, cook foods thoroughly
  • Avoid high-risk animal contact (esp. reptiles) for at-risk groups

PROGNOSIS

  • Uncomplicated gastroenteritis: Excellent, self-limited
  • Worse prognosis: Infants, elderly, immunocompromised, bacteremia/invasive infection, MDR strains

COMPLICATIONS

  • Toxic megacolon, shock
  • Abscess, endocarditis, meningitis, septic arthritis, osteomyelitis, pneumonia, cholecystitis
  • Reactive arthritis

ICD-10 CODES

  • A02.25 Salmonella pyelonephritis
  • A01.02 Typhoid fever with heart involvement
  • A01.3 Paratyphoid fever C

CLINICAL PEARLS

  • Most nontyphoidal Salmonella causes self-limited diarrhea; supportive care is key.
  • Antibiotics only for high-risk or complicated cases.
  • Bacteremia/invasive disease requires aggressive treatment.
  • Infants, elderly, and immunocompromised are at highest risk for complications.
  • Contact with reptiles is a significant source of multidrug-resistant Salmonella.