E. coli O157:H7 From Raw Milk in a Tennessee Cow-Share, 2022

Shiga toxin-producing Escherichia coli (STEC) causes foodborne illness that can lead to hemolytic uremic syndrome (HUS), a life-threatening form of kidney failure. A 2022 outbreak in Tennessee, reported in CDC's MMWR, shows the danger raw milk poses — especially to young children.

Two sick infants

On August 9, 2022, the Tennessee Department of Health identified STEC infections in two 10-month-old infants whose diarrhea began on July 25 and August 1.

• One developed HUS, needing hemodialysis and 27 days in the hospital.
• The other was hospitalized for one day and did not develop HUS.

Both lived in households that drank raw milk from the same cow-share program, and at least one infant had reportedly drunk it. Neither household was a formal cow-share member; they got the milk from participants.

At the farm

The farm owner lived in a rural area with no phone service or electricity, so a health department employee first visited in person to explain the investigation and get the list of cow-share participants. An inspection on August 15 found:

• seven to 10 cows, milked by hand every day;
• possible routes for fecal contamination during milking;
• milk possibly stored warmer than recommended, cooled by circulating spring water and then by putting containers in ice-filled coolers.

Investigators sampled a milk filter, a collection pail, barn posts, four manure locations and raw milk.

Finding more cases

The cow-share had 125 participants in Georgia, Tennessee and North Carolina. The health department found phone numbers for 109 and reached 50 of them (40%), from households with 112 people. One household had three probable cases, with symptoms beginning July 20 that had since resolved, though they weren't lab-confirmed. In all, five cases were identified, including the two confirmed infants; no one died.

The genetic link

The state lab isolated STEC O157:H7 from the second infant's stool; delayed testing prevented isolating it from the first. A U.S. Department of Agriculture lab found two O157:H7 isolates in a cattle manure sample from the farm's milking barn. Whole genome sequencing showed the human and cattle isolates were highly related, with zero allele differences.

Raw milk and the law

In Tennessee, selling raw milk directly is prohibited and the health department advises against drinking it, but sharing raw milk through cow-share arrangements is legal. Because this cow-share planned to keep distributing milk, the University of Tennessee Extension's agriculture team visited the farm on August 30 to teach practices that lower the risk of contamination, and participating households were mailed a letter about the risk of foodborne illness from raw milk.

Lessons

• Raw milk causes outbreaks and individual cases of foodborne illness. Children under 5, adults 65 and older, and people with weakened immune systems face the greatest risk of severe illness, and young children are at particular risk of STEC-related HUS.
• Pasteurization reduces the risk, but raw milk rules vary by state and by point of sale.
• Illness can reach households that aren't formal cow-share members.
• Environmental sampling made it possible to tie the illnesses to the farm.

Sources

• Thomas CM, Marr JH, Durso LM, et al. "Notes from the Field: Shiga Toxin-Producing Escherichia coli O157:H7 Linked to Raw Milk Consumption Associated with a Cow-Share Arrangement — Tennessee, 2022," MMWR Vol. 72, No. 17, CDC; a work of the United States government in the public domain.