Boston authorities say that 57 people may have been infected by a city paramedic accused of tampering with vials of drugs.

A spokesperson for the city public health department said that at least 57 people treated in a city-run ambulance may have been exposed to blood-borne illnesses, according to AP. Officials say that the unidentified paramedic may have tampered with syringes full of sedatives and painkillers during a six-week period in the summer of 2011.

The Boston Public Health Commission said that they have informed all potential victims and offered free medical testing.

Officials said that seven more patients who may have received the tainted drugs have passed away but their deaths are believed to be unrelated to the possible drug contamination.

A criminal investigation is in progress, and that the unidentified paramedic, who had been fired last summer, is so far not facing any charges.

"As part of an ongoing investigation initiated by Boston EMS into misconduct by one of its uniformed paramedics, the department has notified 57 patients that they potentially received compromised medications during EMS treatment," Boston Emergency Medical Services said in a statement. "The 57 patients received doses of controlled medications that may have been tampered with by the suspected employee during a six week period in the summer of 2011."

"All 57 patients have been offered free screening for infectious diseases, and the Boston Public Health Commission is running an incident hotline staffed by trained clinicians to answer questions and provide information to these individuals. However, the department is not aware of the suspect having or transmitting an infectious disease to any patients," Boston EMS concluded.