A Centers for Disease Control report has identified the likely cause of a 2017 outbreak of E. coli infections among Marine Corps recruits at the service’s West Coast boot camp as “undercooked beef” and “poor hygiene practices” among recruits.

In October, hundreds of recruits at Marine Corps Recruit Depot San Diego were reported to be suffering from “diarrheal symptoms” following a bacterial outbreak at the facility.

At the time, depot officials said that they had treated a total of 302 patients out of the more than 5,500 recruits in training.

Officials found illness in recruits at both the depot and Edson Range, Camp Pendleton, California, a field training location used by recruits.

A report released from the Annual Epidemic Intelligence Service Conference gave a brief synopsis of the CDC investigation into the outbreak.

Report authors noted that E. coli infections can cause a serious condition called Hemolytic-Uremic Syndrome, or HUS. The syndrome can destroy red blood cells and cause kidney failure.

CDC medical staff assisted the U.S. Navy to a response to the outbreak. They took stool specimens from those with symptoms and categorized samples.

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Through sampling they identified:

62 confirmed E. coli infections

62 suspected cases with a diagnosis of probable HUS or evidence of E. coli

120 with bloody diarrhea

Of those tested, investigators noted that 30 required hospitalization and 15 had HUS. In their review they found “poor hygiene practices among recruits” and “inconsistent cooking temperatures within dining facilities.”

After interviewing 43 patients and 135 controls, investigators found a probable link in those who’d consumed undercooked ground beef.