Contaminated Dental Equipment Can Carry HIV
By Susan English
Athens, GA–A recent study entitled “Resistance of microorganisms to disinfection in dental and medical devices” has found that human immunodeficiency virus (HIV) and other human pathogens can survive high level chemical disinfection by hiding in the various greases and oils used to lubricate many of today`s dental and medical devices.
The study, authored by Dr. David L. Lewis at the University of Georgia`s Department of Ecology and by Dr. Max Arens of the Washington University School of Medicine`s Retrovirus Laboratory (St. Louis, MO), raises the specter of cross-infection of patients and underscores the need for more effective sterilization of instruments after each patient use. In the study, researchers investigated whether lubricants can render high level chemical disinfection procedures ineffective, and also addressed the role that some common devices may play in disease transmission.
Disease transmissions were documented for flexible endoscopes, or medical imaging scopes, used in diagnostic and surgical procedures, even after being subjected to high level disinfection. Dental handpieces used for the polishing and drilling of teeth can potentially transfer more blood than is received in a needlestick injury (known to transmit the HIV virus). Prophy (prophylaxis) angles for cleaning and polishing teeth have the potential to transfer sufficient amounts of blood to infect human lymphocyte cultures with HIV.
The results emphasize the need to subject reusable dental devices to a heat-sterilization protocol that penetrates the lubricant. Laboratory studies found that when traces of blood become embedded in lubricants, germicidal chemicals cannot kill even the weakest human pathogens, such as HIV. The studies were conducted using trace quantities of whole blood (100 microliters) from HIV-infected patients. The AIDS virus remained infectious for at least two days, but less than one week, when trapped in the lubricants, even when treated with the recommended 2 percent solution of glutaraldehyde (one of the more powerful chemical germicides).
The authors` previous research demonstrating that dental handpieces could potentially transmit HIV and other infectious agents was published by the American Society for Microbiology in 1992 and in the British medical journal, The Lancet, recommending the adoption of a heat sterilization standard (autoclaving, chemclaving or dry heat) to kill viruses lodged in dental handpieces. For sterilizing flexible endoscopes, automated reprocessing techniques, which flush out traces of contaminated lubricants and other debris, rather than manual disinfection procedures, for purging internal channels with liquid chemical germicides are the preferred method. Even more current research recommends reprocessing endoscopes with a commercial peracetic acid process to remove contaminated lubricants. According to Dr. David Lewis, “Instruments and infection control procedures used in modern medicine and dentistry were developed in a world where most infections were easily treated with various antibiotics, and severely immunocompromised patients were rarely seen. There was a time when we could get by with inserting reused instruments into every orifice of the body without sterilizing them, and blow heavily contaminated water in the mouth when filling teeth. That time has passed.”
The study, supported by the National Association of Dental Laboratories, was published in the September 1 issue of a British medical publication, Nature Medicine, also in The New York Times and The Boston Globe, which picked up the story on August 30 because of the case of a local convenience store owner convinced he contracted AIDS after having had three teeth extracted by a Springfield, MA dentist in late 1989. The case was heard in pre-trial on September 19 and may go to trial this year. The possibility of infection by contaminated dental equipment was first suggested by the man`s doctor at the Lahey Clinic (Burlington, MA). Massachusetts health officials concluded that he had no other risk factors for HIV infection.
Dr. Lewis believes the study`s findings may help explain the mystery surrounding the Acer case in Florida, when a half-dozen patients in the late 1980s were infected, as well as unknown numbers of other AIDS cases in which investigators have found no other risk factor. Among the 441,528 cases of AIDS reported so far by the U.S. Centers for Disease Control and Prevention (CDC), 3 to 6 percent, or as many as 26,280 cases, fall into this category. The problem is to prove that contaminated equipment was the actual source of infection. Unlike hospitals, which keep records on which endoscopes were used on which patients and where medical conditions are usually closely monitored and followed up, dental patients simply “tell their dentists `goodbye` and walk out the door,” says Lewis. If they later become sick with hepatitis, pneumonia, or even AIDS, there is no way to document whether or not the disease originated with a dental device, because no such records are kept. Also, the long incubation period of HIV makes tracking especially problematic, and legal barriers prevent disclosure of patient identities.
Routes of Infection
Use of high-speed dental handpieces provide two potential routes of infection, which occur primarily when patients are exposed to the air/water spray expelled by dental handpieces as the devices are operated inside the mouth: waterborne pathogens and bloodborne pathogens.
With waterborne pathogens, patient blood and saliva retracted into water lines inside handpieces can travel all the way back into the flexible lines that feed water into the handpieces. Therefore, before re-attaching water lines to handpieces after the handpieces have been removed and sterilized, it is recommended that dentists flush them for a couple of minutes. This washes out patient materials that may have been retracted into the lines, leaving behind only those organisms (mostly bacteria) that can cling to the inside walls of lines. These microorganisms multiply in “biofilms” or layers that can shed microbes back out during operation of the equipment, presenting the risk of pneumonia and other diseases, especially high to immunocompromised patients. Lewis recommends the use of filters and chemical treatment of water lines to reduce risks of infection by this route, and the CDC is currently considering recommending such measures.
With bloodborne pathogens, traces of blood withdrawn into airways of handpieces remain largely undiluted with water and become embedded inside the handpiece or in air lines that exhaust away from the patient. This potentially infectious material, mixed with lubricants inside the devices, is impervious to germicides and presents a potential risk of infections such as HIV and hepatitis. Heat sterilization after each patient use can virtually eliminate the risk of transmitting bloodborne infections patient-to-patient, a risk shared by all dental patients if handpieces are merely treated with chemical germicides.
Lewis feels that studies of dentist-to-patient transmission, such as the Acer case, give little insight into the frequency of patient-to-patient transmission, which may be the larger problem. Devices such as non-sealed prophy angles used to clean and polish teeth, are heavily lubricated. If reused on many patients over a short period of time, they can collect visible amounts of blood, which mixes with the grease around internal gears. It is then expelled during later use on other patients. “Once in a while, you can see grease blackened with contamination ooze out of the angles onto a patient`s teeth and get scrubbed into bleeding gums,” says Lewis. Fortunately, most dentists in the U.S., unlike many parts of the world, autoclave prophy angles after each use or use disposable models. He observes that a dentist probably enjoys more safety working with gloves than a patient does with open wounds exposed to blood from previous patients, coming out non-sterilized high speed drills and polishing devices.
Almost any type of infectious disease, from the common cold to the AIDS virus, could potentially be transmitted by contaminated lubricants expelled by dental and medical devices. Patients at highest risk are those with damaged immune systems, such as the elderly, individuals undergoing chemotherapy, organ transplant recipients, and AIDS patients. However, of more concern in this country are the more easily transmitted diseases carried by a large portion of the population such as influenza, cytomegalovirus and infectious hepatitis. HIV, observes Lewis, is probably rarely transmitted by contaminated dental handpieces in the U.S. He admits that so far, dental HIV transmission is rare and that most practices where it does occur probably have only a single case. In a study of a Miami dental practice of 1,300 patients run by a dentist with AIDS, no dentist-to-patient or patient-to-patient transmissions were found, despite the fact that at least 28 patients were HIV positive and the dentist did not sterilize instruments. However, only 20 percent of the patients were tested, giving only a 1-in-5 chance of detecting one transmission. Gene-sequencing was done on only two of the four HIV-positive patients who had no identified risk factors. However, in areas of the world where a high proportion of the population is HIV-infected and where old and worn dental devices are commonly used without heat-sterilizing them, patient-to-patient HIV transmission in dentistry may occur more frequently.
The Acer Case
An abstract of the study published in Nature Medicine lists three ways in which HIV could possibly have been shared by Dr. David Acer and at least six of his patients: (1) Dr. Acer could have bled directly into his patients` mouths during invasive procedures; (2) the virus could have been spread indirectly by contaminated instruments; or (3) he could have intentionally infected his patients. Equipment contamination as a mode of HIV transmission was still deemed highly unlikely because Dr. Acer`s handpieces, including attachments for cleaning teeth (prophy angles) were immersed in 2 percent glutaraldehyde, a powerful chemical germicide that quickly inactivates the AIDS virus. Up until now, it was also believed that the virus could only survive from seconds to a few hours at most in traces of blood outside the body. However, Dr. Lewis`s findings that HIV can survive high-level chemical disinfection when entrapped in lubricants and that it remains infectious for at least several days, makes transmission of HIV by non-sterilized dental devices somewhat more plausible, he says. The fact is that Dr. Acer and at least five of his six infected patients were treated using prophy angles, making it possible that the virus passed among the individuals, especially if the prophy angles leaked. Still, Lewis admits, his and Arens` research do not prove how Dr. Acer`s patients became infected.
Compliance
Recently updated CDC guidelines recommend heat sterilization, or autoclaving, of dental devices. However, Lewis, also a staff scientist at the U.S. Environmental Protection Agency, estimates that 40 to 80 percent of dentists actually autoclave their instruments as they should. This means that if he is correct, 63,000 to 126,000 U.S. dentists are not observing sterilization guidelines. Lewis says better education within the dental community is needed to improve compliance.
In 1992, after the American Society for Microbiology published the findings of research studies in which he had participated, Dr. Lewis met with the FDA, the CDC, and the American Dental Association (ADA). As a result, both the FDA and the CDC undertook a review of infection control guidelines and updating of sterilization guidelines for dentistry. The findings were widely reported throughout the U.S., Canada, Europe, and elsewhere, prompting a review of international infection control guidelines. The CDC published upgraded guidelines for dentistry in 1993, recommending the exclusive use of heat sterilization processes “for all reused devices entering the oral cavity.” Meetings were convened in Denmark, Spain and France to consider whether Europe should adopt the new CDC guidelines for dentistry. Government and dental associations in some countries steadfastly oppose the adoption of these guidelines. In Denmark, for example, the president of the Danish Dental Association was fired last year days after he publicly supported Lewis` conclusions and stated that non-sterilized dental handpieces present a risk of HIV infection. In Denmark, where dental fees are set by the government and children under 18 are treated free of charge, dentists would be responsible for paying for infection control equipment with little or no help from the government. It would cost $100 million for the extra equipment and personnel to achieve the highest level of sterilization. (The U.S. standard is the highest in the world.) Other countries outside Europe, such as Japan, Australia and New Zealand, have already moved to adopt the heat sterilization standard.
The ADA, however, refused to adopt the recommendation that dental handpieces be subject exclusively to heat-sterilization processes, categorizing it as an “Effective and Preferred” method, with the caveat that dentists check with manufacturers as to the ability of the various alloys and materials used in the manufacture of dental products–handpieces and attachments–to withstand high temperatures. Further, it adopted an adversarial position toward the findings and their authors, criticizing the Academy of General Dentistry for publishing some of Lewis`s research and making it clear through its own publications that ADA did not support his conclusions.
In its 1992 revised guidelines, the ADA recommended the use of ethylene oxide gas for sterilizing dental handpieces, also contrary to the study`s findings. Gas sterilization, sometimes used on endoscopes, is effective only on clean, dry surfaces. However, ethylene oxide loses its effectiveness on contact with moisture, and no procedures have been developed to clean and dry the inside of dental handpieces. Lewis maintains that the ADA should not have recommended the procedure at all, citing the case of a Florida man who contracted hepatitis C after having extensive, invasive dental work performed by a dentist who admitted using ethylene oxide on the equipment and that he had not known he was supposed to have dried the instruments before applying it. The ADA says that ethylene oxide is impractical to use and that “dropping it from our recommended sterilants was like telling dentists to stop doing things they never did in the first place!”
Recently, an ADA spokesperson stated that “we`ve actually recommended heat since 1956, but up until as recently as three years ago, high-speed handpieces could not be sterilized because the technology would not allow it.” In July, 1994, the ADA finally did distribute a question and answer handout to 190,000 dentists to give to their patients, citing a recent study in the Journal of the American Dental Association, which stated that “virtually all dentists sterilize their handpiece (drill) between patients” and recommending the use of heat sterilization methods on “dental instruments.” In July, 1995, an ADA news release referred to an ADA “Survey on Infection Control and Handpiece Sterilization” querying 3,000 dentists on their infection control practices. According to the survey, ADA said “92.5 percent of all dentists who responded indicated they heat sterilize their handpieces between patients, up from 25 percent in 1990.” The implication could be drawn that if only one-quarter of the dentists who now say they routinely heat-sterilize equipment were doing so in 1990, the door may have been left open for a wave of HIV or other infections via patient-to-patient transmission through contaminated dental instruments.
Dr. Lewis says that most of the dental professionals he has spoken with about the survey question the accuracy of information gathered by questionnaires. “Now that chemical disinfection of the devices is not recommended and is even illegal in some states, responding that you don`t sterilize handpieces is like filling out a form saying you don`t pay taxes,” says Lewis. Industry sources, he maintains, tell him that, in reality, probably somewhere between 40 to 80 percent of a total of 120,000 U.S. dentists, or between 24,000 and 72,000, now heat sterilize handpieces after every patient use.
“I believe that the majority of dentists understand patients` concerns about sterilizing handpieces and give them a straightforward, honest answer when they ask about it. However, some dentists consider wiping handpieces with chemical solutions to be a form of sterilization. Others just aren`t being completely truthful with patients about their infection control practices,” he says. By not publishing a heat-sterilization standard comparable to the CDC`s, the ADA continues, in his view, to reinforce an attitude persistent among dentists that sterilizing handpieces is only an “overkill measure” to quell unfounded public fears of AIDS. In its new brochure, the ADA recommends “spending a few minutes talking about infection control procedures” with one`s dentist. However, the ADA`s own statistics indicate that only one patient in 20 actually does ask about infection control.
James Sharpe, the Massachusetts convenience store owner who now has full-blown AIDS, said in an interview with The Boston Globe he would advise all dental patients to ask dentists if they autoclave, or heat-sterilize, their instrument before each use. “It is your right, as John Q. Patient, to say, `Are you autoclaving?` and `Prove it.` ” n