What are the causes and treatments of E coli (Escherichia coli) infections?

E. coli Infections: Causes and Treatment

Causes and Transmission

E. coli infections are caused by pathogenic strains of Escherichia coli bacteria that have acquired specific virulence factors, transmitted primarily through contaminated food, water, animal contact, and person-to-person spread. 1

Major Pathogenic Categories

E. coli causes distinct clinical syndromes based on the pathotype involved 2:

• Shiga toxin-producing E. coli (STEC): Causes acute, often bloody diarrhea and can progress to life-threatening hemolytic uremic syndrome (HUS) in approximately 8% of O157:H7 cases 1
• Enterotoxigenic E. coli (ETEC): Major cause of travelers' diarrhea and infant diarrhea in developing countries 3, 2
• Enteropathogenic E. coli (EPEC): Important cause of infant diarrhea 2
• Enteroinvasive E. coli (EIEC): Causes dysentery 2
• Uropathogenic E. coli (UPEC): Most common cause of urinary tract infections 3, 4

Transmission Routes

STEC transmission occurs through 1:

• Consumption of undercooked ground beef, unpasteurized juice, raw milk, and raw produce (lettuce, spinach, alfalfa sprouts)
• Ingestion of contaminated water
• Direct contact with animals or their environment
• Person-to-person spread (particularly in childcare settings)
• Critical point: O157 STEC and O111 STEC have an extremely low infectious dose (<100 organisms), making them highly contagious 1

Treatment Approach

For STEC Infections (Including E. coli O157:H7)

Aggressive fluid management is the ONLY proven effective treatment for STEC infections, while antibiotics must be avoided due to increased risk of HUS. 5, 6

Fluid Management Protocol

• Mild to moderate dehydration: Reduced osmolarity oral rehydration solution (ORS) as first-line therapy 5, 6
• Severe dehydration, shock, altered mental status, or ORS failure: Isotonic intravenous fluids (lactated Ringer's or normal saline) 5, 6
• Early and aggressive parenteral volume expansion is crucial to prevent HUS development 1, 5

Critical Contraindications for STEC

Never use antibiotics for STEC O157 or other Shiga toxin 2-producing strains - multiple retrospective studies show higher HUS rates with antimicrobial treatment, and in vitro data demonstrate increased Shiga toxin production with certain antibiotics 6

Never use antimotility agents (e.g., loperamide) as they increase HUS risk 6

Monitoring Requirements

Close surveillance for HUS development is mandatory, particularly in children under 5 years who face the highest risk 5, 6:

• Monitor for the HUS triad: thrombocytopenia, hemolytic anemia, and renal failure 5
• Continue monitoring even after diarrhea resolves, as HUS can develop days later 5

For Non-STEC E. coli Infections

Urinary Tract Infections

FDA-approved antibiotic options include 3, 7:

• Ciprofloxacin: Indicated for UTIs caused by E. coli, including complicated UTIs and pyelonephritis 3
• Trimethoprim-sulfamethoxazole: Indicated for UTIs caused by E. coli 7
• Important caveat: Global surveillance shows 17.9% of E. coli isolates are ESBL-producers, with ciprofloxacin susceptibility as low as 14.6% in ESBL-positive strains 8
• Carbapenems (ertapenem, imipenem) remain most active, inhibiting >98% of all E. coli phenotypes 8

Pediatric Considerations for Fluoroquinolones

Ciprofloxacin is FDA-licensed for complicated E. coli UTIs and pyelonephritis in patients 1-17 years of age, but is not first-choice due to increased musculoskeletal adverse events (9.3% vs 6.0% in controls) 1, 3

Fluoroquinolone use in children may be justified only when 1:

• Infection is caused by multidrug-resistant pathogens with no safe alternative
• Parenteral therapy is not feasible and no other effective oral agent is available

Infectious Diarrhea (Non-STEC)

• Ciprofloxacin: FDA-approved for infectious diarrhea caused by enterotoxigenic E. coli when antibacterial therapy is indicated 3
• Trimethoprim-sulfamethoxazole: FDA-approved for traveler's diarrhea due to enterotoxigenic E. coli 7

Diagnostic Imperatives

All stools from patients with acute community-acquired diarrhea should be simultaneously cultured for E. coli O157:H7 AND tested with Shiga toxin assays - regardless of patient age, season, or presence of blood in stool 1, 5

Specimens should be collected 5:

• As soon as possible after diarrhea onset
• While patient is acutely ill
• Before any antibiotic administration

Public Health Requirements

All confirmed STEC cases must be reported to public health authorities for outbreak detection and control 5

Food-service workers and childcare attendees may require negative follow-up cultures before returning to work/school per state regulations 5