A University of Hong Kong investigation has blamed a nurse for a blunder in which dental kits were not sterilized properly before being used on patients at its clinic.
About 250 students, teachers and their families were affected by the incident from October 30 to November 2.
A dental nurse may have forgotten to press the "start" button on an autoclave - where dental instruments are placed for sterilization - or did not press the button hard enough to start the procedure on the afternoon of October 30, said HKU professor Yuen Kwok-yung, who headed a three-member investigation team.
The report from the month-long investigation showed that it is likely that the dental nurse then did not check whether the autoclave indicated "Ready," an indication for the completion of the autoclaving cycle, and affirm the color of the printout from the autoclave that can suggest whether the sterilization procedure has been completed.
Staff subsequently unloaded the instrument packages from the autoclave and put them in storage for use.
However, the investigation team failed to identify the nurse who made the mistake.
Since the workload for autoclaving was quite heavy, dental staff on duty on October 30 could not recall if they had performed the autoclave duty that afternoon.
The team suggested that the clinic staff record the date and time after the sterilization procedure is completed to avoid reccurence of the blunder.
Dental Association vice president Wong Chi-wai said: "Using the autoclave is an essential last step in cleaning dental tools because it is the only way to kill some strong viruses including HIV and hepatitis B.
"The incident is weird as it is absolutely rare for any dentist or their staff to forget to use the autoclave."
After the blunder, the dental clinic at the University of Hong Kong called on 248 patients to take blood tests for HIV and hepatitis B and C.
All but one who could not be reached by the university, eventually tested negative for HIV virus and hepatitis C. Some were already hepatitis B carriers before the incident.
However, HKU student union president Dan Chan Koon-hong said he is disappointed that the investigation team failed to identify the staff member who should be held responsible for the blunder.
The Department of Health, which supervises clinics, said last night: "Prevention of transmission of blood-borne diseases in health-care settings, including dental clinics, is achieved through proper adherence to infection control measures laid down by each institution, based on the principles of standard precautions."