Health bosses say 651 people who used a piercing and tattoo studio in Newport have now attended clinic appointments for precautionary health checks.
Concerns were raised after five people with serious skin infections were treated as hospital in-patients.
The confirmed cases could also indicate a low risk of transmission of Hepatitis B and Hepatitis C and an extremely low risk of HIV transmission for all clients of these premises.
A blood test to check for Hepatitis B, Hepatitis C and HIV has been offered.
The local health board says clinic slots are still available and health staff are encouraging anyone that has had a procedure carried out at the premises to come forward for the test.