Crispian Scully and Stephen R. Porter Infection control in dentistry. Current Opinion in Infectious Diseases Nosocomial and hospital-related infections. August 1994 : 488-492.
Outline
* Abstract
* Aspects of viral transmission in dental practice
o Human immunodeficiency virus
* Potential routes of parenteral transmission in dentistry
* Professional recommendations
* Conclusion: education and policing
* References and recommended reading
Transmission of infectious agents between dental health care workers and patients continues to be of concern. Improved infection control procedures, including appropriate vaccination, has significantly reduced the risk of occupational acquisition of hepatitis B virus and there is currently little data of transmission of hepatitis C virus in the dental clinic. Transmission of HIV to dental health care workers has not been documented; transmission from an HIV-infected dental health care worker to six patients has been reported but the route of transmission is still not known. While standards of infection control have significantly improved in the past decade, staff compliance with appropriate procedures remains variable, and other weaknesses in cross-infection control in dental practice still remain. Concerns about possible infection transmission in dentistry are not new. Herpes simplex virus, hepatitis B virus (HBV), hepatitis D virus, Mycobacterium tuberculosis and Pseudomonas spp. are among the several agents that have been proved to be transmissible in dental practice in the absence of correct infection control measures [1.1], but other agents may also be transmissible. There has been a growing appreciation by both dental health care workers (DHCWs) and patients [2.1] of the need for improvements in infection control measures in dentistry. Guidelines have been issued in the USA, UK and many other countries. Legal and disciplinary actions have been implemented in some instances where infection control has been shown to be lacking. Public and professional concerns have been heightened with the emergence of the AIDS epidemic, which has also increased awareness of infections such as hepatitis C virus (HCV) (and their possible sequelae). The evident transmission of HIV from a dentist to at least six patients in one Florida dental practice [3.1], and the recognition that at least some instances of infection with hepatitis viruses and with HIV, have no recognizable source have added to these concerns. Important questions are therefore raised as to whether some dental, medical or paramedical practices are responsible for infection transmission and, in this respect, the media have rightly expressed concern.
Aspects of viral transmission in dental practice
Although the possibility of transmission of bloodborne infections such as HBV from DHCWs to patients is considered to be small, precise risks have not been quantified. Reports published from 1970 to 1987 indicate nine clusters in which patients were infected with HBV, associated with treatment by an HBV infected DHCW [4.1]. Nonetheless, transmission of HBV from dentists has not been reported since 1987, possibly reflecting such factors as incomplete ascertainment and reporting, increased adherence to universal precautions including routine glove use by dentists and increased levels of immunity resulting from the use of hepatitis B vaccine. However, isolated sporadic cases of infection are more difficult to link with a health care worker (HCW) than are outbreaks involving multiple patients. Most DHCWs in developed countries have now been immunized against HBV [5 .1]. When 30 000 dentists and clinical ancillary staff in the UK were surveyed in July 1991 to assess the current state of immunization against HBV, about 11 000 responded immediately and nearly 94% of these had been, or were being, immunized against HBV [6.1]. Nearly all dentists and therapists (94% in each group), 95% of hygienists and 96% of dental surgery assistants, had been immunized. However, about 53% of most responding clinical dental staff had been vaccinated 4 to 5 years before the survey, and out of these, nearly 81% had not had booster immunization [6.2]. Consequently, booster immunization is now indicated for many dental clinical personnel. In many developing countries, HBV vaccination of dentists is still not optimal [7.1].
There is some evidence to suggest that parenteral non-A non-B hepatitis may have been transmitted during dental treatment, but there is no data indicating transmission of HCV as a result of dental treatment. HCV RNA can be present in the saliva of up to 50% of patients with acute and chronic HCV infection [8.1][9.1][10.1][11.1][12.1][13.1]. Salivary HCV RNA may correlate with viraemia [13.2], but there is no epidemiological data to suggest that salivary transmission of HCV is frequent. HCV transmission from a human bite has, however, been reported [14.1]. Current evidence suggests that HCWs are not at a notable risk of HCV acquisition as a result of occupational exposure, unless they sustain a needlestick injury [15.1][16.1][17.1][18.1][19.1][20.1][21.1]. The risk of HCV infection following a needlestick injury with HCV-contaminated blood may be as high as 10%, although in recent prospective studies only three out of 174 HCWs and DHCWs who sustained a needlestick injury with blood from HCV-infected patients subsequently became HCV-seropositive [20.2] [21.2]. Although dental staff in low prevalence areas, for example, in the UK [22.1] and even in high prevalence areas, for example Taiwan [23.1], do not have a raised incidence of HCV infection, some dental health care staff in the USA have been found liable to HCV carriage [24.1][25.1]. Nonetheless, the risk of occupational transmission of HCV to DHCWs is far less than that of HBV.
The Florida dental case is the only known instance of HIV transmission as a consequence of treatment by an infected DHCW [26.1][27.1]. Another study found no HIV transmission from a different HIV-infected DHCW [28.1]. In the latter study, there were 1192 patients who had undergone 9267 procedures, 124 patients were deceased. A review of the death certificates of these deceased patients identified five who had died with HIV infection, but all of these were either homosexual males or users of illicit intravenous drugs. The investigators located 962 (92%) out of the remaining 1048 patients and 900 agreed to be HIV tested. Infection with HIV was documented in five out of these 900 patients, and four patients had clear evidence of risk factors for acquiring HIV infection. The other patient had only one examination by the dentist and denied high-risk behaviour. Comparative RNA sequence analysis demonstrated that the viruses from the dentist and these five patients were not closely related. Studies of 19 063 other patients have failed to find any other individuals who have become infected with HIV as a result of treatment by HIV-infected HCWs, including dentists and dental students [3.2]. In particular, transmission did not occur during 369 previous hours of general surgical exposure [29.1], and one HIV-infected orthopaedic surgeon who regularly sustained sharps injuries from instruments every 1-3 weeks and more substantial bone spicule cuts about every month [30.1] did not transmit HIV to any treated patient. Detailed investigations suggest that the risk of HIV transmission from HCW to patient is mathematically very close to zero [31.1]. The low risk of transmission of HIV is further demonstrated by the knowledge that possibly only one of over 7000 tested DHCWs was thought to have acquired HIV as a result of nosocomial exposure to the virus [32.1]. Retrospective studies of patients exposed to an HIV- infected HCW (look-back studies) may, however, fail to accurately assess the rate of HIV transmission. This is because patients may have died or cannot be contacted, or do not wish to be tested or subjected to public scrutiny, or both [31.2]. As a consequence of these limitations it may be more advantageous to search for a history of surgery or dental work by an HIV-infected HCW in HIV patients with no identifiable risk factor for HIV acquisition.
Potential routes of parenteral transmission in dentistry
Much conventional dental practice involves exposure-prone invasive procedures and therefore carries the risk of inoculating microorganisms should the equipment used be infected. This would be especially possible when penetrating or cutting instruments breach the epithelium. HBV, and possibly HIV, infections have probably been transmitted from DHCWs to patients, rather than from one patient to another, but exactly how some of the infections have been transmitted is unclear. Evidence of possible patient-to-patient transmission of HIV through the use of surgical equipment is still equivocal [32.2][33.1]. There is no doubt that DHCWs can commonly suffer sharps injuries [34.1], which could be routes of transmission of infection, at least to the DHCW. The wearing of protective gloves does not reduce the frequency of sharps injuries but may confer some protection by virtue of their wiping action on the sharp object on penetration. Double gloving may, however, not be of any significant advantage overall [35.1]. Dental local anaesthetics are supplied sterile in cartridges and are administered through needles which are intended to be disposable. The latest evidence indicates that needles and cartridges are not usually reused. This is important because blood and body fluids can enter the needle and cartridge [36.1]. Likewise, scalpel blades and discs for cutting tooth material are intended to be disposable. To date, many dental practices have used metal bands to help form a matrix to place restorations, and these have the potential to breach the epithelium. The bands have not always been discarded between patients, although they should be sterilized. Dental burrs, brushes and the like should also be discarded after use, or sterilized, as some restorations lie beneath the gum margin and the epithelium is damaged quite frequently by the instrument. Handpieces for holding these instruments, and hand held instruments should also be heat sterilized before use on another patient [36.2]. Unfortunately, current evidence shows that although the use of autoclaves has, and is, increasing, some 50% of surveyed UK dental practices do not regularly autoclave instruments between patients [6.3][37.1]. Time, cost and inconvenience presumably explain why such dental practices have not adopted the use of autoclaves and many complain that instruments are damaged by the process. In some instances, this has resulted in a lack of sterilization of dental handpieces. A recent survey indicated that 2890 (43.9%) out of 6588 surveyed UK dentists sterilized or disinfected handpieces after each patient [6.4]. Another study showed that only 50.5% correctly used autoclaving [37.2]. Furthermore, not all practitioners are wholly compliant with infection control measures, even when they are provided with all the appropriate equipment [38.1]. The possible risk from infection with dental handpieces has been highlighted in recent professional publications [39.1][40.1] and the media. In one study a dye was used to simulate material from a patient, and was either applied externally to, or injected into the waterline of, dental handpieces. The internal air turbine chambers became contaminated and the material was only slowly dislodged during subsequent use of the dental handpiece [39.2]. This suggested a possible locus for infected material and reinforced the need to adequately heat-sterilize handpieces before they are used on another individual. Restricted physical access, particularly to internal surface of dental handpieces, limits cleaning and disinfection with liquid chemical germicides. Surface disinfection by wiping or soaking in liquid germicides is not an acceptable method for reprocessing high-speed handpieces, low-speed handpiece components used intraorally or reusable prophylaxis angles. Retraction valves in dental unit water lines may cause aspiration of patient material back into the handpiece and water lines, therefore anti-retraction valves (one-way flow check valves) have been installed in new units to prevent fluid aspiration and to reduce the risk of transfer of potentially infective material. Routine maintenance of anti-retraction valves is necessary to ensure effectiveness. High-speed handpieces should be run to discharge water and air for a minimum of 20-30 s after use on each patient. This procedure is intended to help the physical flushing out of patient material that may have entered the turbine and air or waterlines, but it is not an effective method of cleaning debris from the handpiece. Use of an enclosed container or high-velocity evacuation should be considered to minimize the spread of spray, spatter and aerosols generated during discharge procedures. Additionally, there is evidence that overnight or weekend microbial accumulation in water lines can be reduced substantially by removing the handpiece and allowing water lines to run and to discharge water for at least 3 min at the beginning of each clinic day [39.3]. The water coolant used in the high-speed handpiece and ultrasonic scaler can become infected, not only with oral organisms but also with Pseudomonas and legionellae [41 .1]. Although there is no evidence that such a contaminated water supply poses a significant risk to healthy individuals it may constitute a hazard to immunocompromised persons [42.1]. Unfortunately, neither chlorination nor charcoal filtration of the water supply reliably decontaminates it [41.2][43.1]. At present, the absence of reliable and practical sterilization for the waterlines of dental units is an area of weakness in all cross-infection control of dental offices.
Recently, recommended infection control procedures for dentistry have been comprehensively outlined [36.3][44.1]. These recommendations should reduce the risk of disease transmission in the dental environment, from patient to DHCW, from DHCW to patient, and from patient to patient. The Centers for Disease Control and Prevention guidelines [36.4] delineate specific recommendations related to DHCWs. These include the following.
(1) protective attire and barrier techniques; 2) handwashing and the care of hands; (3) the appropriate use and care of sharp instruments, needles and handpieces; (4) sterilization or disinfection of instruments; (5) cleaning and disinfection of the dental unit and environmental surfaces; (6) disinfection of the dental laboratory; (7) anti-retraction valves and other intraoral dental devices attached to air and water lines of dental units; (8) single-use disposable instruments; (9) the handling of biopsy specimens; (10) use of extracted teeth in dental educational settings; (11) disposal of waste materials; and. (12) implementation of recommendations.
Conclusion: education and policing
There is little doubt that infection control has been improving in dentistry in many countries over the past decade. However, there is still room for progress, and with the prevalence of HIV and associated infections such as tuberculosis, still rising in the general population, this is of increasing importance. Education of DHCWs is required [45.1], however, this is no guarantee of effective clinical practice [46.1]. Consequently, there is an additional need for the development of more rapid, uncomplicated and inexpensive, efficient methods of sterilization and disinfection. Legal requirements are increasing, for example in the UK the Health and Safety Executive can visit any dental practice at any time to assess standards of infection control and has the power to prohibit dental practice and have the dentist liable for prosecution [47.1]. The UK General Dental Council endorses current infection guidelines and indicates strongly that failure to employ adequate methods of cross-infection control may render a dentist liable to proceedings for misconduct [48.1]. Several dentists have suffered disciplinary proceedings as a consequence of employing inadequate infection control.
References and recommended reading
1. C Scully, RA Cawson, MJ Griffiths: Occupational Hazards to Dental Staff. Br Dent J 1990,
2. SR Porter, G Peake, C Scully, LP Samaranayake: Attitudes to Cross-Infection Measures of UK and Hong Kong Patients. Br Dent J 1993, 175: 254-256. This study of UK and Hong Kong patients reveals that patients remain concerned about likely transmission of HIV during dental treatment and increasingly expect dental staff to wear protective clothing to minimize all infection transmission in dental practice.
3. Investigation of Persons Treated by HIV-Infected Health Care Workers: United States. MMWR 1993, 42: 329-337. An excellent summary of 19 063 patients treated by HIV-infected HCWs in the USA. Only six patients were found to be HIV-infected after treatment by a Florida dentist with AIDS. Several other HIV-infected dental HCWs were also examined but there was no other evidence of them transmitting HIV to patients.
4. DM Bell, CN Shapiro, BF Gooch: Preventing HIV Transmissions to Patients, During Invasive Procedures. J Public Health Dent 1993, 53: 170-173.
5. C Scully, M Griffiths, C Blake, L Chartres: The Control of Cross-Infection in UK Clinical Dentistry in the 1990s: Immunisation Against Hepatitis B. Br Dent J 1993, 174: 29-31. In a survey of almost 11 000 UK dental staff, over 96% had been immunized against hepatitis B virus. About 53% of the staff had been vaccinated 4-5 years before the survey but only 81% of them had not had a booster immunization.
6. C Scully, C Blake, M Griffiths, H Levers: Protective Wear and Instrument Sterilisation/Disinfection in UK General Dental Practice. Health Trends 1994, 26: 21-22.
7. C Scully, J Jorge: Hepatitis B Vaccination and Infection Control in Brazilian Dental Practice. Community Dent Oral Epidemiol 1991, 19: 225-227.
8. TC Liou, TT Chang, KC Young, XZ Lin, CY Lin, HL Wu: Detection of HCV RNA in Saliva, Urine, Seminal Fluid and Ascites. J Med Virol 1992, 37: 197-202.
9. S Ogasawara, M Kage, KI Kosai, K Shimamatsu, M Kojiro: Hepatitis C Virus RNA in Saliva and Breast Milk of Hepatitis C Carrier Mothers [Letter]. Lancet 1993, 341: 561. HCV RNA was detected in five out of 10 HCV-infected mothers. Breastmilk did not contain HCV RNA.
10. JT Wang, TH Want, JT Lin, JC Sheu, SM Lin, DS Chen: Hepatitis C Virus RNA in Saliva of Patients with Post-Transfusion Hepatitis C Infection [Letter]. Lancet 1991, 337: 48.
11. K Takamatsu, Y Koyanagi, K Okita, N Yamamoto: Hepatitis C Virus RNA in Saliva [Letter]. Lancet 1990, 336: 1515.
12. K Abe, G Inchauspe: Transmission of Hepatitis C by Saliva [Letter]. Lancet 1991, 337: 248.
13. JT Wang, TH Wanf, JC Sheu, JT Lin, DS Chen: Hepatitis C Virus IsimNA in Saliva of Patients with Post Transfusion Hepatitis and Low Efficiency of Transmission Among Spouses. J Med Virol 1992, 36: 28-31.
14. GM Dusheiko, M Smith, PJ Scheuer: Hepatitis C Virus Transmitted by Human Bite. Lancet 1990, 336: 503-504.
15. LB Seeff: Hepatitis C From a Needlestick Injury [Letter]. Ann Intern Med 1991, 115: 411.
16. F Petrarulo, P Maggai, A Sacchetti, G Pallotta, F Dagostino, C Basile: HCV Infection Occupational Hazard at Dialysis Units and Virus Spread Among Relatives of Dialysis Patients. Nephron 1992, 61: 302-303.
17. A Vaglia, R Nicolin, V Puro, G Ippolito, C Bettini, F DeLalla: Needlestick Hepatitis C Virus Seroconversion in a Surgeon. Lancet 1990, 336: 1315-1316.
18. E Cariani, A Zonaro, D Primi, E Magni, C Incarbone, P Scalia, E Tanzi, G Zehender, AR Zanetti: Detection of HCV RNA and Antibodies to HCV after Needlestick Injury [Letter]. Lancet 1991, 337: 850.
19. TK Blackmore, P Maddocks, NH Stace, P Hatfield: Prevalence of Antibodies to Hepatitis C Virus in Patients Receiving Renal Replacement Therapy, and in the Staff Caring for Them. Aust NZ J Med 1992, 22: 253-357.
20. T Sodeyama, K Kioyosawa, A Urushihara, A Matsumoto, AE Tanak, S Furuta, Y Akahane: Detection of Hepatitis C Virus Markets and Hepatitis C Virus Genomic RNA after Needlestick Accidents. Arch Intern Med 1993, 153: 1565-1572. Three out of 90 health care workers became HCV-infected as a result of sustaining a needlestick injury contaminated with virus from HCV-infected patients. While HCV infection by needlestick injury may be important, such transmission does occur.
21. ME Hernandez, M Bruguera, T Puyuelo, JM Barrera, J Rodes: Risk of Needlestick Injuries in the Transmission of Hepatitis C Virus in Hospital Personnel. J Hepatol 1992, 16: 56-58.
22. AM Herbert, CM Walker, KI Davies, J Bagg: Occupationally Acquired Hepatitis C Virus Infection [Letter]. Lancet 1992, 339: 305.
23. MY-P Kuo, LJ Hahn, CY Hong, JH Kao, DS Chen: Low Prevalence of Hepatitis C Virus Infection Among Dentists in Taiwan. J Med Virol 1993, 40: 10-13.
24. RS Klein, K Freeman, PE Taylor, CE Stevens: Occupational Risk of Hepatitis C Virus Infection Among New York City Dentists. Lancet 1991, 338: 1539-1542.
25. ER Schiff, MA Hill, G Johnson: Prevalence of Anti-HCV in the VA Dental Environment from 1979-1981 [Abstract]. Hepatol 1990, 12: 849.
26. CA Ciesielski, D Marianos, CY Ou, R Dumbaugh, J Witte, R Berkelman, B Gooch, G Myers, CC Luo, A Lasch, K Bell, N Economau, B Scott, L Furman, J Curran, H Jaffe: Transmission of Human Immunodeficiency Virus in a Dental Practice. Ann Intern Med 1992, 116: 798-805. 27. CY Ou, CA Ciesielski, G Myers, CI Bandea, CC Luo, BT Korber, JI Mullins, G Schochetman, RL Berkelman, AN Economau, J Witte, LJ Furman, G Satten, K MaCinnes, J Curren, HW Jaffe: Molecular Epidemiology of HIV Transmission in a Dental Practice. Science 1992, 256: 1165-1171.
28. GM Dickinson, RE Morhart, NG Klimas, CI Bandea, JM Laracuente, AL Bisno: Absence of HIV Transmission from an Infected Dentist to his Patients. An Epidemiologic and DNA Sequence Analysis. JAMA 1993, 269: 1802- 1806. A review of the HIV status of patients treated by an HIV transmission from an HIV-infected dentist. There was no evidence of HIV transmission from the dentist to any traced patient.
29. AS Rogers, T Townsend, T Gordon, AJ Brown, EC Holmes, LQ Zhang, KC Parsonnet, JE Abramson, MG Smith: Investigation of Potential HIV Transmission to the Patients of an HIV-Infected Surgeon. JAMA 1993, 269: 1795-1801. No evidence of HIV transmission from an HIV-infected general surgeon to patients was found, despite over 300 h of general surgical procedures and high standards of cross-infection control.
30. TT Gilbert, FE Sha, KC Parsonnett, JE Abramson, MG Smith: Absence of HIV Transmission from an Infected Orthopedic Surgeon. A 13-Year Look-Back Study. JAMA 1993, 269: 1807-1811. No evidence of HIV transmission from an HIV-infected orthopaedic surgeon to patients was found, despite the surgeon's injuries from bone spicule during operation.
31. B Mishu, W Schaffer: HIV-infected Surgeons and Dentists. Looking Back and Looking Forward [Editorial]. JAMA 1993, 269: 1843-1844. Current data regarding patients treated by HIV-infected health care workers is reviewed. The results indicate that the retrospective nature of such studies may underestimate any nosocomial transmission of HIV, as not all patients can be contacted, will be scrutinized, or undergo HIV testing. There still remains a small possibility of nosocomial HIV transmisssion from dental health care worker to patient.
32. B Gooch, U Marianos, C Ciesielski, R Dumbaugh, A Lasch, H Jaffe, W Bond, S Lockwood, J Cleveland: Lack of Evidence for Patient-to-Patient Transmission of HIV in a Dental Practice. J Am Dent Assoc 1993, 124: 38-44.
33. K Chant, D Lowe, G Rubin, W Manning, D Lyle, M Levy, S Morey, J Kaldor, R Garsia: Patient-to-Patient Transmission of HIV in Private Surgical Consulting Rooms. Lancet 1993, 342: 1548-1549.
34. C Siew, B Chang, SE Gruninger, AC Verrusio, EA Neidle: Self-Reported Percutaneous Injuries in Dentists: Implications for HBV, HIV Transmission Risk. J Am Dent Assoc 1992, 123: 37-44.
35. LG Upton, HD Barber: Double-Gloving and the Incidence of Perforations During Specific Oral and Maxillofacial Surgical Procedures. J Oral Maxillofac Surg 1993, 51: 261-263. Wearing 2 pairs of protective rubber gloves does not eliminate possible skin perforations during oral and maxillofacial surgery. Perforation was probably likely when bone fragments, screws, plates or wires were included during long procedures and was constantly pressing on the surgeons dominant hand.
36. Recommended Infection-Control Practices for Dentistry 1993. MMWR 1993, 42: 1-12. An excellent review of cross-infection control in dental practice which considers all areas of weakness in cross-infection control, including the use of extracted teeth for teaching restorative dentistry.
37. J Bagg, A Ashraf: Cross-Contamination with Dental Equipment [Letter]. Lancet 1993, 341: 180. Not all dental practices in the UK actually employ heat sterilization procedures.
38. C Scully, M Haj, S Porter: Infection Control in Dentistry [Letter]. BMJ 1993, 306: 1754. Despite receiving additional appropriate training and being provided with protective clothing and equipment, the compliance of dental health care workers in aspects of infection control remains low.
39. DL Lewis, RK Boe: Cross-Infection Risks Associated with Current Procedures for Using High-Speed Dental Handpieces. J Clin Microbiol 1992, 30: 401-406.
40. DL Lewis, M Arens, SS Appleton, K Nakashima, J Ryu, RK Boe, JB Patrick, DT Watanabe, M Suzuki: Cross-Examination with Dental Equipment. Lancet 1992, 340: 1252-1254.
41. CL Pankhurst: The Microbiological Quality of Water in Dental Chair Units. J Hosp Infect 1993, 23: 167-174. A review of the likely sources of contamination of water in dental chair units. Measures that may reduce microbiological contamination are discussed in detail.
42. MV Martin: The Significance of the Bacterial Contamination of Dental Unit Water Systems. Br Dent J 1987, 163: 152-154.
