Escherichia coli (E coli): What IPC Professionals Should Know

Escherichia coli (E coli) is a type of bacteria commonly found in the lower intestine of warm-blooded animals and is the most commonly identified organism in urinary tract infections. E coli is ubiquitous in the gastrointestinal tract of humans and animals, although many strains are nonpathogenic. Uropathogenic E coli (UPEC) strains possess several virulence mechanisms—including structural features like flagella and fimbriae and the production of secreted toxins—that enable them to colonize the urinary tract and cause infection.

Once E coli is shed in feces, it can be transferred from the perianal area to the urethral opening during toileting (eg, wiping back-to-front), during sexual activity, or during urinary catheterization. Because the female urethra is shorter than in males and near the perianal area, UTIs are much more common in females.

It’s well known that foodborne E coli can cause diarrheal illness; a recent study published in One Health uncovered a fascinating link between food supply E coli and urinary tract infection. Researchers examined genomic “fingerprints” of E coli isolates from Flagstaff, Arizona, hospital inpatients with UTI and compared patterns with E coli strains from raw chicken, turkey, and pork sold in local grocery store chains. While causation isn’t proven from this study, the correlation between strains was compelling: researchers estimate that around 8% of extraintestinal E coli infections in humans, mostly UTIs, are attributable to foodborne zoonotic E coli. This study highlights the ecosystem's complex interplay between animals, humans, and bacteria.

While many strains of E coli are harmless, Shiga toxin-producing E coli (STEC) strains are frequent culprits in causing severe disease, including bloody diarrhea. The incubation period is usually 3-4 days post-exposure but may range from 1 to 10 days. Symptoms of STEC infection include severe stomach cramps, diarrhea—often bloody—and vomiting. If there is a fever, it is usually typically less than 101 F/ 38.5 C For most patients, symptoms resolve within 5–7 days. Around 5–10% of patients diagnosed with STEC infection develop hemolytic uremic syndrome (HUS), which manifests as anemia, low platelets, and kidney failure. While most patients with HUS recover within a few weeks, others may die of this complication or have permanent kidney damage.

The CDC estimates that 265,000 STEC infections occur annually in the US, causing 3,600 U.S. hospitalizations and 30 deaths annually. The most commonly identified STEC in North America is E. coli O157:H7 (often expressed simply as 0157), estimated to cause about 36% of STEC infections. Less is known about non-0157 STEC strains; in general, they are less likely to cause severe illness or hemolytic uremic syndrome.

Groups at higher risk for severe illness from STEC include children younger than 5 years old, adults over age 65, and patients with immunocompromise (eg, due to HIV, diabetes, or cancer therapy). However, people of any age can become infected and seriously ill.

E coli infections begin with swallowing trace amounts of human or animal feces. Environmental sources include contaminated pond water and contact with animals. During the slaughter of farm animals, E coli from their intestinal tracts can contaminate raw meat and poultry; feces can then come into contact with kitchen tools and surfaces during food preparation and may persist in undercooked meat. Other foodborne sources include unpasteurized milk or cider, soft cheese made from raw milk, or contaminated lettuce. Transmissions can occur from eating food prepared by someone whose hands are contaminated with traces of feces from toileting, livestock work, or from touching animals in petting zoos.

During the early years of the COVID-19 pandemic, reports of enteric foodborne infections, in general, were lower than in previous years. However, a CDC report confirmed that in 2022, foodborne infection rates returned to pre-pandemic levels—and in the case of Shiga toxin-producing E coli (STEC), the annual incidence was higher than before the pandemic. Examples of E coli outbreaks in 2022 included infections resulting from ground beef shipped in meal kits and frozen falafel.

The CDC recommends 4 food safety steps to prevent foodborne E. coli infection:

• Clean: Wash hands, utensils, and surfaces often. Wash fruits and vegetables before eating, cutting, or peeling them. Thoroughly clean hands after toileting, changing diapers, or touching animals (even in your backyard).
• Separate: Avoid cross-contamination. Keep foods that won’t be cooked separately from raw foods and their juices, including raw meat, poultry, seafood, and eggs.
• Cook: Use a food thermometer to ensure food is cooked to a temperature high enough to kill bacteria.
• Chill: Refrigerate perishable food within 2 hours or 1 hour if food is exposed to temperatures above 90°F, such as in a hot car. Thaw food in the refrigerator, not on the counter.

To prevent uropathogenic E coli in the perianal area from entering the urethra, wipe from front to back during toileting. It is recommended to urinate following sexual activity to flush bacteria from urethral tissue. Reduce the use of urinary catheterization when possible and use the proper technique before and during insertion.

To reduce worsening antimicrobial resistance from E coli and other bacteria, clinicians should have ready access to localized susceptibility and resistance data to guide prescribing decisions. Diarrheal infections from STEC, including 0157, are treated supportively—antibiotics have not been shown to be helpful. However, when treating E coli UTIs in hospitalized patients, prescribers should follow guidance based on institutional antimicrobial susceptibility data. For ambulatory patients, geolocated antimicrobial susceptibility data are free in the epocrates Bugs + Drugs app.