Three dental clinics were shut down in Philadelphia because of conditions that may have exposed patients to diseases such as HIV, said the city's health department.
Three locations of the Trieu Family Dental Clinic were shut down by the Philadelphia Department of Public Health in early December 2018 for conducting procedures with instruments that may not have been properly cleaned.
Letters were sent to patients to determine who had visited the clinics since January 2017, encouraging them to get tested for HIV as well as the hepatitis B and hepatitis C viruses, said the department.
"We do not know how long these unsatisfactory practices were taking place, so we are encouraging anyone who had a visit at one of the three Trieu dental practices in Philadelphia to speak with their regular healthcare provider as soon as possible," read a statement from the health department emailed to USA TODAY.
The health department said it's not aware of any infections caused by the practices at the clinics.
The Pennsylvania Department of State is also investigating the dental clinics' practices.
The health department has been working with the clinics to update their practices and identify former patients.