A study published in The New England Journal of Medicine this week shows that an outbreak of bacterial skin infections in upstate New York is linked to a bad batch of tattooing ink. The outbreak of Mycobacterium chelonae infections occurred in the Fall of 2011 around the Rochester, New York area. The infection caused raised rashes on at least 19 people’s tattoos.

The study, which was a joint effort between the Monroe County Department of Public Health, the New York State Department of Health, the University of Rochester medical Center, Clinton Crossings Dermatology, the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration, began when a dermatologist notified Rochester officials of a Mycobacterium chelonae infection in one of his patients. The common link of the tattoos was determined, and the cause was tracked to a gray ink used by a single tattoo artist in Rochester.

The artist had purchased the ink from a supplier at a tattoo trade show in Arizona. Investigators inspected the manufacturer’s operation, but did not find contaminated materials. The manufacturer voluntarily recalled the bad batch, and the unopened samples of the ink that investigators were able to test also contained the bacteria.

18 of the 19 patients that were identified as having the infection were treated successfully with antibiotics. The 19th “declined evaluation and treatment.”

The CDC states that bacterial contamination of tattoo ink can be caused by contaminated ingredients, poor manufacturing practices, or dilution with water that isn’t sterile.