For the study, researchers analyzed more than 5,700 E. coli isolates from both UTI patients (2,349 isolates) and retail meat samples (3,379 isolates), purchased concurrently in the same residential areas as the clinical isolates between February 2017 and May 2021. The human clinical and retail meat samples covered eight counties in Southern California.

Using a genomic attribution model, the team traced the likely origin of each bacterial strain, distinguishing between human and animal sources. Demographic, clinical, and antimicrobial resistance profiles were compared between meat isolates and clinical isolates inferred to be of human or food-animal origin.

The researchers’ analysis revealed that:

• 18 percent of UTIs were linked to E. coli strains of animal origin, suggesting foodborne transmission
• Turkey (82 percent) and chicken (58 percent) samples tested positive for E. coli most frequently
• The highest-risk strains were most frequently found in chicken (38 percent) and turkey (36 percent); a small subset of E. coli lineage from meat was disproportionately responsible for a large portion of the strains identified in human clinical urine samples
• E. coli contamination was higher from meat samples purchased in areas with higher poverty rates, with a 12 percent increase in contamination for each 10% absolute increase in regional family poverty rate
• Individuals in low-income neighborhoods faced a 60 percent higher risk of foodborne UTIs compared to those in higher-income areas
• Women and older men were identified as particularly vulnerable populations
• Meat and zoonotic E. coli isolates tended to show lower resistance to clinically relevant classes of antimicrobials, except for tetracyclines, and gentamicin resistance was significantly higher in meat isolates than both zoonotic and non-zoonotic clinical isolates.

The latest findings follow similar research led by George Washington University and published in 2023, which also suggested that E. coli infection from contaminated meat products may be responsible for hundreds of thousands of urinary tract infections in the U.S. each year.

UTIs are among the most common infections globally, with significant economic impacts due to medical costs and lost productivity. While E. coli is a known contaminant in raw meat, this study provides one of the first quantifiable estimates of its role in causing UTIs through foodborne transmission.

The researchers caution that further investigation is needed to refine host-origin prediction models, differentiate foodborne transmission from other exposure pathways, and assess the applicability of these findings beyond Southern California. Future projects will also explore bloodstream infections and other serious E. coli-related illnesses.

Credited as senior author of the study is Lance B. Price, Ph.D., Professor of Environmental and Occupational Health at George Washington University. The project was supported by the Wellcome Trust, the U.S. National Institute of Allergy and Infectious Diseases (NIAID), and the Johns Hopkins Sherrilyn and Ken Fisher Center for Environmental Infectious Disease Discovery Program.