When Chobani Greek yogurt consumers complained of stomach problems in September 2013, the company issued a recall, but when symptoms reportedly worsened in healthy people over time, researchers took a closer look. Initially, the Food and Drug Administration (FDA) thought the Mucor circinelloides fungus that contaminated the products only sickened those with compromised immune systems, but it wasn’t until it started to harm healthy people that researchers decided to take a closer look at the fungal strain, and published their findings in the journal mBio.

"When he heard about the Chobani recall after reports of people becoming sick from yogurt contaminated with Mucor circinelloides, we thought the M. circinelloides strain could cause more serious problems than one might think,” the study’s co-author Soo Chan Lee of Duke University said in a press release.

More than 200 Chobani yogurt consumers suffered vomiting, nausea, and diarrhea after consuming yogurts contaminated with the M. circinelloides mold. According to the FDA report, illnesses became very severe, and one person experienced “repeated vomiting and diarrhea for two entire days and two days of missed work” while their spouse only experienced severe diarrhea and nausea for a few days. Researchers obtained the yogurt from the couple’s fridge and confirmed the mold, which had previously been thought to pose “little or no risk to consumers,” but that was based on an evaluation from the Chobani breakout. It turns out it’s capable of causing significant infections and reactions in humans.

Before the outbreak, scientists didn’t know the potential harm this fungal strain could inflict on humans. Researchers even tested the particular strain on mice and found it had the ability to cause lethal infections when directly injected into the bloodstream.

When Chobani CEO Hamdi Ulukaya was asked in 2013 about the outbreak, he said the voluntary recall “totally fixed” the issue and said the mold became a problem because the company doesn’t use preservatives in its products, according to USA Today. Customers described the products as “unnervingly fizzy” and described it as tasting like wine.

"When people think about food-borne pathogens, normally they list bacteria, viruses, and maybe parasites. Fungal pathogens are not considered as food-borne pathogens. However, this incidence indicates that we need to pay more attention to fungi. Fungal pathogens can threaten our health systems as food-borne pathogens," Lee said.

Source: Heitman J, Cuomo CA, Ko DC, et al. Analysis of a Food-Borne Fungal Pathogen Outbreak: Virulence and Genome of a Mucor circinelloides Isolate from Yogurt. mBIO. 2014.