Fatal French HUS Outbreak Caused by Globally Emerging, Hybrid E. Coli Strain Affected Only Adults

Why It Matters

The outbreak underscores the rising risk of severe STEC infections in adults and the need for enhanced food‑borne pathogen monitoring, especially for emerging hybrid strains that can evade traditional pediatric‑focused surveillance.

Key Takeaways

• Hybrid STEC/ETEC O77:g:K92:H18 caused 18 confirmed adult cases
• 90% of patients developed HUS, three deaths reported
• Raw cow’s milk cheese identified as source; recall issued Jan 2025
• Strain carries stx2d toxin and ETEC enterotoxin genes
• Global database shows 31 related strains across three continents since 2005

Pulse Analysis

The French outbreak shattered conventional expectations that hemolytic uremic syndrome (HUS) is primarily a pediatric concern. In a six‑month window, 18 adults—median age 72—were infected, and more than nine‑tenths progressed to HUS, a rate far exceeding the 3‑24% typically seen in adult STEC cases. The three fatalities highlight the severe clinical trajectory when virulent strains bypass age‑related immunity, prompting health officials to reevaluate adult‑focused surveillance protocols.

Genomic analysis identified the culprit as a LEE‑negative STEC/ETEC hybrid, serotype O77:g:K92:H18, harboring the stx2d Shiga toxin variant alongside classic ETEC enterotoxin genes. This combination amplifies gut colonization and systemic toxin delivery, explaining the unusually high HUS incidence. The strain’s rare K92 capsule may further enhance evasion of host defenses. A review of EnteroBase uncovered 31 closely related isolates spanning Europe, Asia, and North America dating back to 2005, signaling that this hybrid pathotype has been silently disseminating across continents.

The outbreak’s link to raw cow’s milk cheese underscores persistent food safety gaps in unpasteurized dairy products. Traceback investigations, aided by loyalty‑card data, enabled a swift recall, yet the incident illustrates the difficulty of detecting contamination in artisanal supply chains. French authorities have now mandated PCR‑based STEC screening for adult HUS cases, a move other nations may emulate. Strengthening genomic surveillance, improving raw‑milk handling standards, and fostering cross‑border data sharing are essential steps to curb the spread of this emerging hybrid pathogen and protect vulnerable adult populations.