Background: On July 16, 2019, clinical leadership at the University of Washington School of Dentistry received a report from a dental assistant that a dental student was not following standard sterilization procedures for dental burs. These are the small drill bits that are used to remove decay and prepare teeth for restoration such as fillings or crowns.
Instead of bringing used burs to Central Processing (the sterilization facility) immediately after patient treatment per the standard procedure, this student was reported to be placing the used burs in a storage locker that also contained the sterilized burs belonging to that student. If the student stored both sterilized and non-sterilized burs in the locker, we cannot be certain that the student used only sterilized burs. An immediate investigation was performed to confirm the report, and patient records for the student were reviewed to determine which patients could have been exposed to burs that were not sterilized. The investigation also looked into rubber dam clamps that could have been similarly unsterilized.
How many patients were potentially affected?
- The incident was limited to one student, and we have identified 18 patients who could have been affected.
How are patients being notified?
- We have sent certified letters to the identified patients letting them know of the incident and the extremely low risk, and our offer to test them for possible infection. We have also posted a notification on the homepage of our website. Patients who have questions not covered on this page should call 206-616-6153.
What will these patients be tested for?
- Testing will be offered for hepatitis B, hepatitis C, and HIV (human immunodeficiency virus). These infections are transmitted by exposure to blood, which would be uncommon during restorative dental procedures.
What is the risk of infection from this incident?
- The risk is extraordinarily low. A dental bur spins at high speed (about 300,000 RPM) while a spray of water under pressure continually washes across it. It is used to prepare teeth for restorations and, while it could be exposed to saliva, it is not normally exposed to blood. Vacuum suction is used to remove the water. The risk of transmitting an infection via a dental bur is extremely small.
What is the scientific basis for the risk assessment?
- There are no known studies of transmission of infectious diseases from unsterilized dental burs or dam clamps. The best scientific information about infection transmission risk comes from studies and data where there is a known risk. For example, we know the risks from accidental needle stick injuries. In these cases, the risk is normally one encountered by a health care professional who has an occupational accident with a contaminated instrument. The risk of transmitting HIV after an accidental needle stick where the needle contained HIV-positive blood is 0.2% to 0.5% (the average is 0.3%, or 3 out of every 1,000 cases). The risk for hepatitis C transmission with this type of accident is 0% to 10% (the average is 1.8%, or less than 2 out of every 100 cases). The risk for hepatitis B transmission is greater but has a large range that depends upon the type of hepatitis B virus that a patient might have. In addition, many people have been vaccinated for hepatitis B, and that normally eliminates the risk. The reason that there is a range for the risk is that some needles are used to draw blood and others are used to inject a medication. The ones that draw blood hold more blood inside and are riskier than an injection needle. Also, if a needle has been used with an HIV-positive, hepatitis-B-positive, or hepatitis-C-positive patient, some patients have higher levels of virus in their blood than do others.
- This information from the Centers for Disease Control and Prevention demonstrates the low risk of disease transmission after a relatively high-risk accident involving direct exposure to blood. Since a dental bur is far less invasive and does not carry blood, the risk after exposure to a non-sterile dental bur is nearly zero.
How are dental burs and other instruments sterilized?
- Dental instruments that have had any contact with a patient undergo a multi-step process for sterilization and safety. First, they are scrubbed to remove any visible debris. When the shape or design of an instrument does not allow debris to be removed by scrubbing alone, it is placed in a disinfecting solution in an ultrasonic bath to remove smaller particles that are not visible. After that, they are placed in bags or instrument boxes, sealed, and placed in an autoclave – a device that sterilizes them with high temperature, steam, and pressure. The sealed containers are then stored in an area reserved for sterilized instruments until they are retrieved for use.
What procedures are used to confirm that instruments are sterilized prior to use?
- Multiple controls are in place to ensure that all contaminated instruments are sterilized prior to being used. When dental students need instruments for a procedure, they must sign out a sterile sealed instrument cassette (metal box) containing the sterile instruments from Central Processing. When the student completes the procedure, the instruments are placed back in the cassette and returned to Central Processing. Central Processing closely monitors the inventory of the instruments and ensures they are properly sterilized as described above. If students require a special individual instrument that is not part of a standard instrument cassette, they must also sign this out from Central Processing. These types of instruments are sterilized and stored in individual autoclave bags to ensure that they stay sterile. All containers of instruments, whether in cassettes or bags, are inventoried. Boxed instruments are marked with a strip of autoclave tape that changes color after going through the autoclave cycle. Bagged instruments have an indicator dot on the outside of the bag that changes color when the items have been processed in the autoclave. The changed color of the tape or dot lets the user know that the contents of the box or bag have been through autoclave sterilization. In addition, autoclaves are tested every day to make sure they are functioning properly, using a biological indicator (a spore testing strip) that is run through an autoclave cycle and then tested to confirm appropriate sterilization function.
Has this happened before with this student or other students?
- We have investigated this event and are not aware of this occurring previously with this student or others since modern infection prevention measures were implemented decades ago.
How has this incident been addressed with students?
- The student involved in this incident was counseled immediately. In addition, all other students were notified about this incident and received refresher instruction regarding mandatory infection prevention procedures. Students treat patients only under the close supervision of faculty dentists.
It’s been more than a month since the incident took place. Why has it taken this long to issue a public response?
- We had to conduct a comprehensive review of all student records to determine whether sterilization protocols were followed. For the one student involved in the incident, we had to review all patient records going back to the beginning of the year (when this student started treating patients who required the use of burs) to determine where a bur or a rubber dam might have been used. This required a careful case-by-case search of patient records, which is time-consuming.
What are you doing to prevent a similar incident in the future?
- We continue to provide regular education regarding required infection prevention measures and require all students, faculty, and staff who provide patient care to receive annual training and updates on these protocols. We monitor all instruments that are checked out and returned to Central Processing. We continue to ensure that all our instruments and equipment used in patient care are sterilized according to Washington State law and/or Centers for Disease Control and Prevention policy.
- Staff and faculty are verifying, at chairside, that the sterilization indicator on the packaging has changed color (from pink to brown) prior to students opening packages for patient care.
- We are providing additional training specifically targeting this issue at our upcoming Blood Borne Pathogens Training and at future student orientations prior to their entering clinical service.
Are you considering any additional changes to prevent this type of incident?
- Students will be assigned a designated facility in the clinic area for the storage of their sterilized instruments that is closer and more convenient for them to access.
- We are now tracking individual burs issued by the school’s dispensary to ensure even tighter control over inventory.
For more information, please call us at 206-616-6153.