At least two men may have come down with a rare bacterial skin infection that is hard to treat with antibiotics after getting tattoos at a store in Seattle, US health authorities said yesterday.

One 44-year-old man was confirmed to have a case of Mycobacterium haemophilum after getting a tattoo on his arm in the western US city in August 2009, the Centres for Disease Control and Prevention said.

The infection, which showed up as a bumpy red rash and a pus infection on the skin’s surface, resisted treatment with several antibiotics but eventually disappeared after nine months.

A second suspected case was reported in a 35-year-old man who got a tattoo at the same place two months later, but tests were inconclusive. The CDC said it considered it a “suspected” instance of infection.

The source of the bacteria remains a mystery. Authorities said the tattoo parlour was in compliance with safety regulations but told the owner to use sterilised water for rinsing skin and diluting ink instead of tap water.