Lax monitoring by surgery assistants was to blame for improper sterilisation of some dental instruments at a University of Hong Kong clinic in October, investigators reported on Wednesday. Normally instruments are sterilised in a four-step process, but on October 30, one batch of instruments was put through only three of the steps. The instruments were then used on 248 patients between October 30 and November 2. In its report released on Wednesday, a four-member investigation panel said the blunder was caused by a “very rare” lapse by the on-duty dental surgery assistants. On October 30, dental staff at the clinic probably did not press the “start” button on an autoclave – a sterilising oven – scheduled at 2.15pm, and did not check its indicator and printout to make sure it was operating. The panel noted that the autoclave workload was quite heavy, amounting to three to four loadings per day. On October 30 employees could not recall if they had completed the sterilisation process, partly because they were so busy, it said. Using an autoclave is essential because it is the only way to kill some viruses, including HIV and hepatitis B, Dental Association president Sigmund Leung Sai-man said. The 248 people who used the clinic during that period have had their blood tested for HIV and hepatitis B and C. They were mostly students, staff and their family members. The report said 247 of them showed negative results for HIV and hepatitis C virus antibodies. One person could not be contacted. A majority of the patients already had immunity to hepatitis B while a small number were chronic carriers of the virus. Hepatitis B immunisation was offered to 84 potentially susceptible patients.