auentistrv

Risk and prevention of transmission of infectious diseasesin dentistryMarcelo W. B. Araujo, DDS, MSVSebastiano Andreana, DDS, MS^

Health care providers are at risk tor infection with bloodborne pathogens, including hepatitis B virus,human immunodeficiency virus, and hepatitis C virus. Recommended infection control practices areapplioable to all settings in which dental treatment is provided. Dentists remain a! low risk tor occupation-ally acquired human immunodeficiency virus. Dental health care workers, through occupational exposure,may have a 10 times greater risk ot becoming a chronic hepatitis B carrier than the average citizen.Tuberculosis is caused by fi/iycobacterium tuberculosis. In general, persons suspected of having puimo-nary or laryngeal tuberculosis should be considered infectious if they are coughing, are undergoingcough-inducing or aerosol-generating procedures, or have sputum smears positive for acid-fast bacilli.Although the possibility of transmission of bloodborne infections from dental health care workers topatients is considered to be small, precise risks have not been quantified by carefully designed epidemic-logic studies. Emphasis should be placed on consistent adherence to recommended infection controlstrategies, inciuding the use of protective barriers and appropriate methods of sterilization or disinfection.Each dental facility should develop a written protocol for instrument reprocessing, operatoty cleanup, andmanagement of injuries. Such efforts may iead to the üeveiopment of safer and more effective medicaldevices, work practices, and perscnai protective equipment. (Quintessence Int 2002:33:376-382)

Key words: bloodborne, dental health care workers, hepatitis B, human immunodeficiency virus, infectioncontrol, tuberculosis, waterborne

Health care providers are at risk for infection withbloodborne patbogens, including bepatitis B virus

(HBV), human immunodeficiency virus (HIV), andhepatitis C virus (HCV). Fear of HIV transmissionand acquired immunodeficiency syndrome (AIDS) hasheightened awareness of the importance of occupa-tional exposure as a source of infections. As a result,the need to develop efíeetive prevention methods hasfinally assumed a high priority in hospital infectioncontrol programs.' Although the principles of infec-tion control retTiain unchanged, the availability of newtechnologies, materials, equipment, and data necessi-tates continuous evaluation of current infection con-

'Cllnlcal Instructor, Departmenl ot Penodontology and Endodontics, StateUniversity of New York al Buffalo, School of tJental Medicine, andResearcti Assistant, Department ol Social and Preventive Medicine, StateUniverslly of New York at Bulfalo, Sctiool of Medicine, Bjffalo, New York.

^Clinical Assistant Protessor, DeparlmenI of Periodontology and Endo-dontics and DeparlmenI of Oral and Maxillofacial Surgery, State Universityot New York at Buffalo, School of Dental tifledicine, Buffalo, New York.

Reprint requesls: Dr Marcelo W. B. Araujo. Clinrcal Insiructoi, Departmentof Periodontology and Endodontics, State University of Mew York at Buffalo,School of Dental Medicine, 3435 Main Street, 250 Sqjire Hall, Buffalo,New York t4214. E-mail: araujo® a csu. buffalo edu

trol practices. The uniqtie nature of most dental proce-dures, instrumentation, and patient care settings alsomay require specific strategies directed to the preven-tion of transmission of pathogens among dental healthcare workers (DHCWs) and their patients. Recom-mended infection control practices are applicable toall settings in whicb dental treatment is provided.^

Dental patients and DHCWs tnay be exposed to avariety of microorganisms via blood, oral, or respira-tory secretions. Tbese microorganisrns may includecytomegalovirus. HBV, HCV, berpes simplex virustypes 1 and 2, HIV, Mycobacterium tuberculosis,stapbylococci, streptococci, and other viruses and bac-teria-specifically, those that infect the upper respira-tory tract.

Infections may be transmitted in the dental opera-tory through several routes, including direct contactwith blood, oral fluids, or other secretions; indirectcontact with contaminated instruments, operatoryequipment, or etwironmental surfaces; or contact withairborne contaminants present in either droplet spat-ter or aerosols of oral and respiratory fluids. Infectionvia any of these routes requires that all three of thefollowing conditions (commonly referred to as thechain of infection) be present: a susceptible host; a

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pathogen with sufficient infectivity and numbers tocause infection; and a portal through which thepathogen may enter the host. Effective infecfion con-trol strategies are intended to break one or moreof these "links" in the chain, thereby preventinginfecfion.

A set of infection control strategies common to allhealth care delivery settings should reduce the risk oftransmission of infectious diseases caused by blood-borne pathogens such as HBV and HIV. Because notall infected patients can be idenfified by medical his-tory, physical examination, or laboratory tests, theCenters for Disease Control (CDC) recommends thatblood and body fluid precautions be used consistentlyfor all patients. This extension of blood and body fluidprecautions, referred to as universal precautions, mustbe observed roufinely in the care of all dental patients.In addition, specific actions have been recommendedto reduce the risk of tuberculosis (TB) transmission indental and other ambulatory health care facilities.

TRANSMISSION OF PATHOGENS

HIV and AIDS

The largest collection yet assembled of year-to-yeardata on the seroprevalence of antibody to HIV inpracticing dentists confirms that dentists—like otherhealth care workers-remain at iow risk for occupa-fionally acquired HIV infection.^

For the 1995 study, Siew et aP used a novel diary of2,304 pracficing US denfists to examine the frequencyand nature of percutaneous injuries over one dentist-month. Burs were responsible for most extraoralinjuries (4O''/o), and syringe needles accounted for mostintraoral injuries (32%). The annualized mean injuryrate was 3.35, which represents about a threefolddecrease since 1987.*

Nevertheless, this issue assumed some importancewith the advent of AIDS in 1981 and a higher level ofimportance when the disease's route of transmissionhad been elucidated clearly. Subsequently, the AIDSepidemic focused attention on the potential for diseasetransmission to dental health care providers who areat some risk of percutaneous injuries from needles,burs, and sharp and rotating instruments. The concerncentered on the risks of transmission, first frominfected patient to provider and later from infectedprovider to patient.''

A surveillance study revealed that the likelihoodthat health care workers would become infected as aresult of a percutaneous injury with HlV-contami-nated blood was 0.42%, but It was not known bowoften they sustained percutaneous injuries.''

Hepatitis

Studies have indicated that dental health care workers,through occupational exposure, may have a 10 fimesgreater risk of becoming a chronic hepatitis B carrierthan tbe average citizen.= A study was conductedusing data from US dentists participating from 1987 to1991 in the Health Screening Program at the Ameri-can Dental Associafion's (ADA's) annual session. Tbisstudy included dentists (n = 507) who received tbeirmost recent dose of HBV vaccine within the previous10 months, completed a core questionnaire, and weretested for HBV markers (hepatitis B surface antigen,antibody to hepatifis B surface antigen, and antibodyto hepatitis B core antigen) and were found not tobave evidence of past or present infection.

Tbe objective of this study was to evaluate personaland immunization factors associated wftb seroiogicevidence of HBV vaccine response. Vaccine responsewas most strongly associated with sex, age, and num-her of doses. Factors unrelated to vaccine responseincluded type of vaccine and history of hepatitis.Adherence to tbe recommended number of doses andearly vaccination are critical to adequate protectionagainst hepatitis B infection of dentists, who are oftenexposed to blood and otber body fluids.̂

Hepatifis C accounts for 20% to 40% of all acuteviral bepatitis; between 150,000 and 170,000 newcases are reported in the United States each year.Approximately 50% of tbese patients will progress tochronicity and the potential for bepatic disorders. Inan average dental practice that treats 20 patients eachday, it is estimated that one patient with bepatitis Cwill be encountered every 2 weeks.

Because numerous dental procedures stress tbeimmune, coagulation, and metabolic systems, a thor-ough understanding of the potential comphcationsimposed by bepatitis C to these systems is essential. Acase study by Wisnom and Kelly' encompasses com-prehensive medical and dental management of thechronic hepatitis C patient. It includes assessment,intervention, and evaluation, as well as projected plan-ning for future treatment.

The hypothesis that health care personnel arc atincreased risk for HCV is based on tbe followingfactors:

1. the well-recognized increased risk of HBV infec-tion among health care personnel

2. the association of this risk to blood exposures3. the demonstration of bloodborne transmission for

both HBV and HCV4. the presence of HCV in blood and saliva5. reports of accidental HCV transmission from needle

stick exposures

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The heahh care personnel with the highest rates ofHBV infection arc dentists and oral surgeons. This isthe population among which increased rates of HCVare expected,'̂

Data reported by Tbomas et al** indicate that occu-pational transmission of HCV to dental personneloccurs sometimes but not frequently. The prevalenceof antibody to HCV in both general dentists and oralsurgeons was not markedly higher than the prevalencein the general population or blood donors in NorthAmerica (0.7% to I.40/0), These data imply that, forgeneral dentists and oral surgeons, the risk of occupa-tional exposure to HBV is greater than the risk ofexposure to HCV. The basis for this difference is prob-ahly the lower quantities of HCV in infected persons,*'

Mycobacterium tuberculosis

Tuberculosis is a clinical illness caused by the bacter-ium M tuberculosis. Effective prevention and controlof M tuberculosis are based on a clear understandingof how TB is transmitted, how infection becomesestablished, and how infection progresses to chnicaldisease. Mycobacterium tuberculosis is spread throughairborne particles, known as droplet nuclei, which canbe generated when persons with pulmonary or laryn-geai TB sneeze, cough, speak, or sing. The particlesare estimated to be 1 to 5 ytm, and normal air currentscan keep them airborne for prolonged time periodsand spread them throughout a room or building.

Infection may occur when a person inhales dropletnuclei containing TB hacilli, which may reach thealveoli, where infection begins. Within 2 to 10 weeks,the hody's immunologie response to TB bacilii usuallyprevents further multiplication and spread. This condi-tion is referred to as latent TB infection.^

Persons with latent TB infection usually have a pos-itive skin test to tuberculin purified protein derivative(PPD), do not have active TB, and cannot infect oth-ers. In the United States, about 90% of infected per-sons remain latently infected for life, with no progres-sion to active TB, In about 5% of persons who havebeen recently infected, active TB disease will developin the first 1 or 2 years after infection, and another 5%will develop disease later in iife. The risk of develop-ing active TB varies with age and immunologie status.^

In general, persons not receiving treatment whohave or who are suspected of having pulmonary orlaryngeal TB should be considered infectious if theyare coughing, undergoing cough-in due ing oraerosol-generating procedures, or have sputum smearsthat are positive for acid-fast bacilli. Persons withextrapulmonary TB are not considered infectiousunless they have concomitant pulmonary disease;nonpulmonary disease located in the respiratory tract

or oral cavity; or extrapulmonary disey '-' that includesan open abscess or lesion. Coinfection with HIV doesnot appear to affect the infectiousness of TB patients.'

Confirmed transmission of HBV and HIV in dentistry

Although the possibility of transmission of bloodborneinfections from DHCWs to patients is considered tobe small, precise risks have not been quantified in thedental setting by carefully designed epidemiologicstudies. Reports published from 1970 through 1987indicate nine clusters in which patients were infectedwith HBV associated with treatment by an infectedDHCW.^ In addition, transmission of HIV to sixpatients of a dentist with AIDS has been reported.'"

Transmission of HBV from dentists to patients hasnot been reported since 1987, possibiy reflecting suchfactors as incomplete reporting, increased adherenceto universal precautions {including routine glove useby dentists), and increased levels of immunity becauseof the use of hepatitis B vaccine. However, isolatedsporadic cases of infection are more difficult to linkwith a health care worker than are outhreaks involv-ing mulfiple paficnts.̂

To determine if patients of a dentist with AIDShecame infected with HIV during their dental care andto identify possible mechanisms of transmission,Ciesielski et al'" developed a retrospective study of thedentist, his office, and his patients. Although the specificincident that resulted in HIV transmission in five of theeight HIV-infected patients remains uncertain, the epi-demiologic evidence supports direct dentist-to-patienttransmission rather than a patient-to-patient route.'"

For hoth HBV and HIV, the precise event or eventsresulting in transmission of infection in the dental set-fing have not been determined; epidemiologic and lab-oratory data indicate that these infections probablywere transmitted from the DHCWs to patients, ratherthan from one patient to another.'"

VACCINES FOR DENTAL HEALTH CARE WORKERS

Although HBV infecfion is uncommon among adults inthe United States (1% to 2%), sérologie surveys haveindicated that 10% to 30Ö/O of health care or dentalworkers show evidence of past or present HBV infec-tion. The US Occupational Safety and Health Admini-stration's rule for bloodborne pathogens requires thatemployers make hepatitis B vaccinations available with-out cost to employees who may he exposed to blood orother infectious materials. In addition, CDC recom-mends that all workers, including DHCWs, who tnightbe exposed to blood or blood-contaminated substancesin an occupational setting be vaccinated for HBV.̂

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RECOMMENDED INFECTION CONTROLPRACTICES FOR DENTISTRY

Emphasis should be placed on consistent adherence torecommended infection control strategies, includingthe use of protective barriers and appropriate methodsof sterilizing or disinfecting instruments and environ-mental surfaces. Each dental facility should develop awritten protocol for instrument reprocessing, opera-tory cleanup, and management of injuries.

Training of all DHCWs in proper infection controlpractices should begin in professional and vocationalschools and he updated with continuing education.^

Use of protective attire andbarrier techniques

For proteetion of personnel and patients in dentalcare settings, medical gloves (latex or vinyl) alwaysmust be worn by DHCWs when there is potentialfor contacting hlood, blood-contaminated sahva, ormucous memhranes. Nonsterile gloves are appropri-ate for examinations and other nonsurgical pro-cedures; sterile gloves should be used for surgicalprocedures.

Before treatment of each patient, DHCWs shouldwash their hands and put on new gloves; after treat-ment of each patient or before leaving the dentaloperatory, DHCWs should remove and discard gloves,and then wash their hands. Dental health care work-ers always should wash their hands and reglovebetween patients. Surgical or examination glovesshould not be washed before use; nor should they bewashed, disinfected, or sterihzed for reuse. Washing ofgloves may cause "wicking" (penetration of liquidsthrough undetected holes in the gloves) and is notrecommended.^

Chin-length plastic face shields or surgical masksand protective eyewear should be worn when splash-ing or spattering of blood or other body fluids is likely,as is common in dentistry. Protective clothing, such asreusable or disposable gowns, laboratory coats, or uni-forms, should be worn when clothing is hkely to hesoiled with blood or other bodily fluids. Impervious-backed paper, aluminum foil, or plastic covers shouldhe used to protect items and surfaces (eg, light handlesor x-ray unit heads) that may hecome contaminatedby blood or saliva during use and that are difflcult orimpossible to clean and disinfect.

Appropriate use of rubber dams, high-velocity airevacuation, and proper patient positioning shouldminimize the formation of droplets, spatter, andaerosols during patient treatment. In addition, splashshields should be used in the dental laboratory.^

Handwashing and care of hands

Dental health care workers should wash their handsbefore and after treating each patient (ie, before gloveplacement and after glove removal) and after bare-handed touching of inanimate objects hkely to be con-taminated by blood, saliva, or respiratory secretions.Hands should be washed after removal of glovesbecause gloves may become perforated during use,and the DHCWs' hands may become contaminatedthrough contact with patient material.

Soap and water will remove transient microorgan-isms acquired directly or indirectly from patient con-tact; therefore, for many routine dental procedures,such as examinations and nonsurgical techniques,handwashing with plain soap is adequate. For surgicalprocedures, an antimicrobial surgical handscrubshould he used.̂

When gloves are torn, cut, or punctured, theyshould he removed as soon as patient safety permits.Dental heahh care workers then should wash theirhands thoroughly and reglove to complete the dentalprocedure.^

Use and care of sharp instruments and needles

Sharp items (eg, needles, scalpel blades, and wires)contaminated with patient blood and saliva should beconsidered as potentially infective and handled withcare to prevent injuries. Used needles shouid never berecapped or otherwise manipulated utilizing bothhands or any other technique that involves directingthe point of a needle toward any part of the body.Used disposable syringes and needles, scalpel blades,and other sharp items should be placed in appropriatepuncture-resistant containers located as close as ispractical to the area in which the itetiis are used.̂

Steriiization or disinfectionof instruments

Indications for sterilization or disinfection. As withother medical and surgical instruments, dental instru-ments are classified into three categories (critical,semicritica!. or noncritical), depending on their risk oftransmitting infection and the need to sterilize thembetween uses. Each dental practice should ciassify allinstruments as follows:

Critical. Surgical and other instruments used topenetrate soft tissue or bone are classified as criticaland should be sterilized after each use.̂

Semicritical. Instruments that do not penetrate softtissues or bone but contact oral tissues are classified assemicritical. These devices should be sterilized aftereach use. If sterilization is not feasible because the

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instrument will he damaged by heat, the instrumentshould receive, at a mitiimum, high-level disinfection.^

Noncritical. Instruments or medical devices thatcome into contact only with intact skin are classifiedas noncritical. Because these noncritical surfaces havea relatively low risk of transtnitting infection, they mayhe reprocessed between patients with intermediate-level or low-level disinfection or detergent and waterwashing, dependittg on the nature of the surface andthe degree and nature of the contamination.'

Cleaning and disinfection of dental units and envi-ronmentai surfaces. After treatment of each patientand at the completion of daily work activities, counter-tops and dental unit surfaces that may have becomecontaminated with patient material should be cleanedwith disposable toweling and an appropriate cleaningagent and water as tiecessary. Sitrtaees then should bedisinfected with a suitable chemical germicide.̂

A chemical germicide registered with the USEnvironmental Protection Agency as a hospital disin-fectant and labeled for tuherculocidal (ie, mycobacte-ricidal) activity is recommended for disinfecting sur-faces that have been soiled with patient material.^

Use and csre of intraoral dentai devices attachedto air lines and dentai unit wateriines. Routinebetween-patient use of a heating process capable ofsterilization (ie, steam under pressure [autoclaving],dry heat, or heat-chemical vapor) is recommended forall high-speed dental handpieees, low-speed hand-piece components used intraorally, and reusable pro-phylaxis angles.̂

Beeause retraetion valves in dental unit wateriinesmay cause aspiration of patient material back into thehandpiece and wateriines, antiretraction valves(one-way flow check valves) should he installed toprevent fluid aspiration and to reduce the risk oftransfer of potentially infective material. High-speedhandpieees should be run to discharge water and airfor a minimum of 20 to 30 seconds after use on eachpatient. This procedure is intended to physically flushout patient material that may have entered the turbineand air lines or wateriines.^

Other reusable intraoral instruments attached to,but removable from, the dental unit air lines or water-lines, such as ultrasonic sealer tips and componentparts and air-water syringe tips, should be cleaned andsterilized after treatment of each patient in the samemanner as handpieees.^

Single-use disposable instruments. Single-use dis-posable instruments (eg, prophylaxis angles, prophy-laxis cups and brushes, tips for high-speed air evacua-tors, saliva ejectors, and air-water syringes) should beused for one patient only and discarded appropriately.These items are neither designed nor intended to becleaned, disinfected, or sterilized for reuse.^

Disposal of waste material^j

Blood, suctioned fluids, or other liquid waste may hepoured carefully into a drain connected to a sanitarysewer system. Disposable needles, scalpels, or othersharp items should be placed intact into puncture-resistant containers before disposal. Solid waste con-taminated with blood or other body fluids should beplaced in seated, sturdy impervious bags to prevetitleakage of the contained items. All contained solidwaste should then be disposed of according torequirements established by local, state, or federalenvironmental regulatory agencies and publishedrecommendations.^

Treatment of water and dental unit wateriines

Backflow prevention devices ean be used to prevetitsiphoning of contaminated fluids into the publicwater supply and are regulated by the health authorityor the plumbing-code enforcement agencies havingjurisdiction."

Jn some locations, water regulators have requireddental offices to install backflow prevention devices atthe service connection or on individuai dental units.Many of these requirements appear to be based otitwo assumptions. First, if a sudden drop in water pres-sure occurs, oral fluids may be aspirated from apatient's mouth into cross-connected water systems.Second, if aspiration does occur, it may result in a sig-nificant risk oí transmission of bloodborne virusesfrom an infected patient to other patients or to per-sons who are using the same water system. Regulatoryinterventions requiring the installation of complexbackflow prevention devices in certain dental officesare based on the conclusion that a high degree of haz-ard of contamination exists. Available science sug-gests, however, that there is an extremely low risk ofsueh contatnination of public water supplies fromcross-connections in dental units."

One concern expressed by local water regulators isthe possibility of contamination of public water sup-plies with bloodborne viruses such as HIV. Scientificevidence indicates, however, that the route of trans-mission of bloodborne viruses is through intimate con-tact with blood or other potentially infectious bodyfluids. Transmission of bloodborne diseases has notbeen reported through the use of any type of watersource and is considered highly unlikely. Unlike bacte-ria or fungi, viruses are unable to reproduce outside aliving host, and any virus introduced into a watersource would he greatly diluted and would probablybecome noninfeetious.

Many persons have expressed fear that HIV mightbe transmitted by contact with waste water, swimming

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pool water, and other water sources. Because tbehepatitis B virus, anotber bloodborne virus, is found inmucb bigher concentrations in blood tban is HIV,HBV is eonsidered a more infectious agent. Studiesshow that the risk of transmission of HBV in sewageand other water is nonexistent; thus, the risk of HIVtransmission would be even smaller."

Possible sites for cross-connection in the dentalunit are the cuspidor, high-speed handpiece. and air-water syringe. Today, most dental offlces do not usecuspidors, and those that are currently manufacturedinclude an air gap, which prevents backflow. Althougha cross-connection is inherent in the design of thehigh-speed bandpiece and air-water syringe, thiscross-connection should he considered very low risk.Both of these devices must have water to operateproperly and, when in use, are observed continually bythe dentist or bygienist. If water flow is disrupted forany reason, tbe dental worker would discontinue useof tbe device. Furtbermore, in tbe unlikely event tbata sudden drop in water pressure caused backflowto occur, the volume of aspirated fluid would beminuscule."

Altbough contamination from cross-connectionsfrom dental units is theoretically possible, availablescientific evidence strongly implies tbat tbis risk isnearly zero. Installation of backflow preventiondevices, when required, should be consistent witb thisvery low degree of hazard. These suggestions arebased on the following facts'^:

1. The human immunodefleiency virus is not trans-mitted by water.

2. There is currently no published evidence of a pub-lic healtb risk due to cross-connections in tbe den-tal unit.

3. The American Water Works Association's state-ment of policy clearly recommends that tbe instal-lation of backflow prevention devices be consistentwitb the degree oí hazard resulting from cross-connections.

4. Increasingly, dentists are using seif-contained den-tal unit water systems that are not connected to thepublic water supply.

Reports in the scientiflc literature suggest that thetnicrobiologic quality of water used in dental treat-ment frequently may not be acceptable for dental caredelivery. Tbis issue was first reported more than 30years ago and recently has resurfaced because of anincreased awareness of potential occupational hazardsand concern about tbe increasing numbers ofimmunocompromised patients seeking dental treat-ment. Levels of microbial eontamination as high as10,000 to 10,000,000 CFUs/mL bave been docu-

mented. As a point of reference, the standard estab-lished by the Federal Safe Water Drinking Act forpotable water is about 500 CFUs/mL of noncoliformbacteria.'-

Tbe current problem with the water quality primar-ily centers on the formation of a microbial biofllmalong the walls of the long, narrow-bore tubing tbatfurnishes cooling and irrigating water to dental handinstruments. Biofilms are formed by microorganisms,sucb as bacteria, fungi, and protozoa, which colonizeand replicate on the interior surfaces of the waterlinetubing, often forming a protective slime layer knownas a glycocalyx. Dental plaque is perbaps the best-known biofilm. Once formed, these biofllms serve as areservoir, signiflcantly amplifying the numbers of free-floating microorganisms in the water exiting thewaterlines.'^

The dental waterline provides an ideal environmentfor microbial colonization. Not only do the materialsused in dental unit construction support tbe formationof biofilms, but also tbe small diameter of tbe tubingcreates a high surface-to-volume ratio for enhancedbiofllm growth,'^

Tbe primary source of the microorganisms is tbepublic water supply. Althougb it is possible thatpatient fluids may be retracted into tbe waterlines dur-ing treatment, current CDC infection control recom-mendations minimize tbe likelihood of tbis occur-renee. Current CDC recommendations include theinstallation and proper maintenance of an tire tractionvalves and tborougb flusbing of dental unit waterlinesat tbe beginning of eacb clinic day and after treatmentof eacb patient. These procedures can assist in flush-ing out patient material that may have entered thewaterlines and may reduce, at least temporarily, over-night or weekend microbial accumulation in water-lines. Flushing of the waterlines, however, does notappear to reduce adherent biofllm in the tubing.'-

in general, most organisms found in dental unitwaterlines are nonpathogenic for immunocompetentpatients. To date, the CDC is unaware of any seriousbealtb effects documented among patients or workerstbat can be directly related to contact witb dentalunit water,'^ In response to these Issues, tbe ADA, in1995, convened an expert panel of representatives ofthe dental profession, governmental agencies, includ-ing the CDC, academia, researcb, and industry. Thepanel developed a statement on dental unit water-lines that was adopted hy the ADA, The ADA'S state-ment on dental unit waterlines can be found at theADA'S website.'^

The panel first acknowledged the existence of den-tal unit water that may be of poor microbiologie qual-ity and estabiisbed a goal for the quality of dental unitwater by tbe year 2000: Water delivered to dental

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pafients during nonsurgical procedures should consis-tently contain no tnorc than 200 CPUs/mL. This goalis based on the quality assurance standard used forhemodialysis units.'^

The panel also identified several preventive strate-gies to improve water quality and identified the needfor development of a convenient and eeonomic deviceto monitor water quality. Preventive strategies toimprove water quality include separate water reservoirsindependent of the public water supply, chemical disin-fecfion of tbe waterline tubing, daily draining and airpurging regimens, and wateriine filters. To date, how-ever, there are insufficient data to establish the effec-tiveness of eacb of these methods. In fact, preliminarydata suggest that none of tbe proposed methodsappears to permanently eradicate biofilms; thus, a com-bination of these strategies may be necessary to controlbiofilm fonnafion and thereby improve water quality."

CONCLUSION

In 1995, Siew et al'' predicted a very low likelihood ofdisease transmission in dentistry. The authors reportedthat it is not likely that an injury rate of zero can beattained unless significant rcengineering of dentalinstruments and equipment takes place and dentistsare impeccable in tfteir compliance with infection con-trol techniques.-* Recent observafional studies amongnondental surgical and operating room personnelhave reported that one or more percutaneous injuriesoccurred during 1% to 15% of procedures. Risk factorsfor percutaneous injuries among surgical personneiinclude surgical specialty; type, durafion, and fime ofday of procedure observed; and the use of certain sur-gical techniques.'*

Additional information is needed for accurateassessment of factors that may increase the risk fortransmission of bloodborne pathogens and otherinfectious agents in a dental setting. Studies shouldaddress tbe nature, frequency, and circumstances ofoccupational exposures. Such information may lead totbe development and evaluation of improved designsfor dental instruments, equipment, and personal pro-tective devices. In addition, more efficient reprocess-ing techniques should be considered in the design offuture dental instruments and equipment. Efforts toprotect both patients and DHCWs should includeimproved surveillance, risk assessment, evaluation ofmeasures to prevent exposure, and studies of postex-

posure prophylaxis. Such efforts may !;•'-' ^" develop-tnent of safer and more effective niclii^al devices,work practices, and personal protective equipmentthat arc acceptable to DHCWs, are practical and eco-nomical, and do not adversely affect patient care.

REFERENCES

1. Gerberding JL. [ncidcnce and prevalence of HIV, HBV,HCV and CMV among health care personnel at risk forblood exposure: Final report trcm a longitudinal study.] infect Dis 1994;170:1410-1417

2. Centers for Disease Control. Recommended infection-controlpractices for dentistrj'. 1993. MMWR l993;42(RR-8]:l-n.

3. Gruninger SE, Siew C, Chang SB, et al. Human immunode-ficiency virus type 1 infection among dentists. J Am DentAssoc 1992; 123:57-64.

4. Siew C, Gruninger SE, Miaw CL, Neidle EA. Percutaneousinjuries in practicing dentists. A prospective study using a20-day diary. ) Am Dent Assoe 1995;126:1227-1233.

5. Wisnoni CI, Lee R). Increased seroprevaience of hepatitis Bin dental personnel necessitates awareness of revised pedi-alric hepatitis B vaecine recommendations. J Ptiblic HealthDent 1993 ;53:231-234.

6. Cleveland |L, Siew C, Locl(wood SA, et al. Factors associ-ated with hepatitis B vaccine response among dentists.I Dent Res 1994;73:1029-1035.

7. Wisnom CJ, Kelly M. Medicai/dental management of achronic hepatitis C patient. A case report. Orai Surg OralMed Oral Pathol 1993;75:78&-790.

8. Thomas DL, Gruninger SE, Siew C, loy E, Qninn T Occu-pational risk of hepatitis C infections among general den-tists and oral surgeons in North America. Am J Med 1996;100:41-45.

9. Centers for Disease Control. Infection control in dentistry-airhorne. Mycobacterium tuberculosis [online]. Availahle:http://www.cdc.gov/nccdphp/ph/icair.htm, Accessed April4, 2000.

10. Ciesielski C, Marianos D, Ou C, et al. Transmission ofhuman immunodeficiency virus in a dental practice. AnnIntern Med 1992; 115:798-805.

11. Centers for Disease Control, ßaekflow prevention and thedental unit [online]. Available: http://www.cdc.gov/nccd-p h p/oh/ha cknow.htm. Accessed April 4, 2000.

12. Centers for Disease Control. Infection control in dentistry-waterhorne. Dental unit waterlines (DUWLs) [online].Available; http://www.cdc.gov/ncedphp/oh/icwater.htm.Accessed April 4, 2000.

13. American Dental Association. American Dental Associationstatement on dental unit waterlines [online]. Available:http : //www. ada.org/prof/prae/issues/statements/lines.html.Accessed April 4, 2000.

14. Cleveland ]L, Lockwood SA, Gooch BF, et al. Percutaneousinjuries in dentistry: an observational study. ] Am DentAssoc 1995;126:745-751.

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