Two more illnesses have been identified in an E. coli outbreak linked to unpasteurized cheese and milk, the Food and Drug Administration reported Thursday. The maker of the products, California-based Raw Farm, continues to deny the link and has refused to issue a recall.

According to the FDA, at least nine people have been sickened in three states, an increase of two cases since the outbreak was announced earlier this month. Three of the nine cases required hospitalization, and one person developed a life-threatening complication called Hemolytic uremic syndrome, or HUS, which causes a type of kidney failure.

Outbreak investigators have interviewed eight of the nine people sickened. All eight reported consuming unpasteurized dairy. One person couldn’t recall a brand, but the remaining seven all singled out products from Raw Farm. Five people ate Raw Farm’s raw cheddar, and two drank Raw Farm’s raw milk. Whole genome sequencing of the E. coli isolates from the patients shows high similarity, suggesting they came from a common source.

The FDA highlighted that the people sickened in this outbreak are young, with over half being less than 5 years old. Children under 5 are particularly vulnerable to severe complications, including HUS, from the type of E. coli in this outbreak, which is a Shiga toxin-producing E. coli, or STEC.

In an infection, STEC makes its way into the intestines and burrows into the mucous layer, where it starts secreting toxin. The toxin can bind to a receptor on certain cells (Gb3) and shut down protein production, causing the cell to die and triggering inflammation. In the progression to HUS, the toxin gets into the bloodstream and takes is cell-killing abilities body-wide. But the tiny blood vessels in the kidney—which have the highest prevalence of receptor Gb3—are most vulnerable. Flooded with toxin, the kidney’s small blood vessels become damaged, red blood cells start bursting, platelets form clots, and the vessels start shutting down entirely, causing parts of the kidney to die and the body to run low on red blood cells and platelets.