本帖最后由 蓝鱼o_0 于 2011-10-28 09:56 编辑
【美国CDC的指南2003】
Dental Unit Waterlines, Biofilm, and Water Quality
Studies have demonstrated that dental unit waterlines (i.e., narrow-bore plastic tubing that carries water to the high-speed
handpiece, air/water syringe, and ultrasonic scaler) can become colonized with microorganisms, including bacteria, fungi, and
protozoa (303–309). Protected by a polysaccharide slime layer known as a glycocalyx, these microorganisms colonize and replicate on the interior surfaces of the waterline tubing and form a biofilm, which serves as a reservoir that can amplify the number of free-floating (i.e., planktonic) microorganisms in water used for dental treatment. Although oral flora (303,310,311)
and human pathogens (e.g., Pseudomonas aeruginosa [303,305,312,313], Legionella species [303,306,313], and nontuberculous Mycobacterium species [303,304]), have been isolated from dental water systems, the majority of organisms
recovered from dental waterlines are common heterotrophic water bacteria (305,314,315). These exhibit limited pathogenic
potential for immunocompetent persons. Clinical Implications Certain reports associate waterborne infections with dental
water systems, and scientific evidence verifies the potential for transmission of waterborne infections and disease in hospital
settings and in the community (306,312,316). Infection or colonization caused by Pseudomonas species or nontuberculous
mycobacteria can occur among susceptible patients through direct contact with water (317–320) or after exposure to
residual waterborne contamination of inadequately reprocessed medical instruments (321–323). Nontuberculous mycobacteria
can also be transmitted to patients from tap water aerosols Health-care–associated transmission of pathogenic agents (e.g., Legionella species) occurs primarily through inhalation of infectious aerosols generated from potable water sources or through use of tap water in respiratory therapy equipment (325–327). Disease outbreaks in the community have also been reported from diverse environmental aerosolproducing sources, including whirlpool spas (328), swimming pools (329), and a grocery store mist machine (330). Although the majority of these outbreaks are associated with species of Legionella and Pseudomonas (329), the fungus Cladosporium (331) has also been implicated. Researchers have not demonstrated a measurable risk of
adverse health effects among DHCP or patients from exposure to dental water. Certain studies determined DHCP had
altered nasal flora (332) or substantially greater titers of Legionella antibodies in comparisons with control populations;
however, no cases of legionellosis were identified among exposed DHCP (333,334). Contaminated dental water might
have been the source for localized Pseudomonas aeruginosa infections in two immunocompromised patients (312).
Although transient carriage of P. aeruginosa was observed in 78 healthy patients treated with contaminated dental treatment
water, no illness was reported among the group. In this same study, a retrospective review of dental records also failed
to identify infections (312).Concentrations of bacterial endotoxin <1,000 endotoxin units/mL from gram-negative water bacteria have been detected in water from colonized dental units (335). No standards exist for an acceptable level of endotoxin in drinking water, but the maximum level permissible in United States Pharmacopeia (USP) sterile water for irrigation is only 0.25 endotoxin units/mL (336). Although the consequences of acute and chronic exposure to aerosolized endotoxin in dental health-care settings have not been investigated, endotoxin has been associated with exacerbation of asthma and onset of hypersensitivity pneumonitis in other occupational settings (329,337).
Dental Unit Water Quality
Research has demonstrated that microbial counts can reach <200,000 colony-forming units (CFU)/mL within 5 days
after installation of new dental unit waterlines (305), and levels of microbial contamination <106 CFU/mL of dental unit
water have been documented (309,338). These counts can occur because dental unit waterline factors (e.g., system design,
flow rates, and materials) promote both bacterial growth and development of biofilm. Although no epidemiologic evidence indicates a public health problem, the presence of substantial numbers of pathogens in dental unit waterlines generates concern. Exposing patients or DHCP to water of uncertain microbiological quality, despite the lack of documented adverse health effects, is inconsistent with accepted infection-control principles. Thus in 1995, ADA addressed the dental water concern by asking manufacturers to provide equipment with the ability to deliver treatment water with <200 CFU/mL of unfiltered output from waterlines (339). This threshold was based on the quality assurance standard established for dialysate fluid, to ensure that fluid delivery systems in hemodialysis units have not been colonized by indigenous waterborne organisms (340). Standards also exist for safe drinking water quality as established by EPA, the American Public Health Association (APHA), and the American Water Works Association (AWWA); they have set limits for heterotrophic bacteria of <500 CFU/mL of drinking water (341,342). Thus, the number of bacteria in water used as a coolant/irrigant for nonsurgical dental procedures should be as low as reasonably
achievable and, at a minimum, <500 CFU/mL, the regulatory standard for safe drinking water established by EPA and APHA/
AWWA.
Strategies To Improve DentalUnit Water Quality
In 1993, CDC recommended that dental waterlines be flushed at the beginning of the clinic day to reduce the microbial
load (2). However, studies have demonstrated this practice does not affect biofilm in the waterlines or reliably improve
the quality of water used during dental treatment (315,338,343). Because the recommended value of <500 CFU/mL cannot be achieved by using this method, other strategies should be employed. Dental unit water that remains untreated or unfiltered is unlikely to meet drinking water standards (303–309). Commercial devices and procedures designed to improve the quality of water used in dental treatment are available (316);methods demonstrated to be effective include self-contained water systems combined with chemical treatment, in-line microfilters, and combinations of these treatments. Simply using source water containing <500 CFU/mL of bacteria (e.g., tap, distilled, or sterile water) in a self-contained water system will not eliminate bacterial contamination in treatment water if biofilms in the water system are not controlled. Removal or nactivation of dental waterline biofilms requires use of chemical germicides.Patient material (e.g., oral microorganisms, blood, and saliva) can enter the dental water system during patient treatment (311,344). Dental devices that are connected to the dental water system and that enter the patient’s mouth (e.g., handpieces, ultrasonic scalers, or air/water syringes) should be operated to discharge water and air for a minimum of 20–30 seconds after each patient (2). This procedure is intended to physically flush out patient material that might have entered the turbine, air, or waterlines. The majority of recently manufactured dental units are engineered to prevent retraction of oral fluids, but some older dental units are equipped with antiretraction valves that require periodic maintenance. Users should consult the owner’s manual or contact the manufacturer to determine whether testing or maintenance of antiretraction valves or other devices is required. Even with antiretraction valves, flushing devices for a minimum of 20–30 seconds after each patient is recommended.
Maintenance and Monitoringof Dental Unit Water
DHCP should be trained regarding water quality, biofilm formation, water treatment methods, and appropriate maintenance
protocols for water delivery systems. Water treatment and monitoring products require strict adherence to maintenance
protocols, and noncompliance with treatment regimens has been associated with persistence of microbial contamination
in treated systems (345). Clinical monitoring of water quality can ensure that procedures are correctly performed and
that devices are working in accordance with the manufacturer’s previously validated protocol. Dentists should consult with the manufacturer of their dental unit or water delivery system to determine the best method for maintaining acceptable water quality (i.e., <500 CFU/mL) and the recommended frequency of monitoring. Monitoring of dental water quality can be performed by using commercial selfcontained test kits or commercial water-testing laboratories. Because methods used to treat dental water systems target the entire biofilm, no rationale exists for routine testing for such specific organisms as Legionella or Pseudomonas, except when investigating a suspected waterborne disease outbreak (244).
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