Epidemiology of Pseudomonas aeruginosa in cystic fibrosis and the possible role of contamination by dental equipment

Microbial Contamination of Dental Unit Waterlines and Potential Risk of Infection: A Narrative Review

Several studies have revealed that dental unit waterlines (DUWLs) are often contaminated by large numbers of various micro-organisms (bacteria, fungi, protozoa, viruses). Microbial contamination in DUWLs may originate from the mains water piped into the dental unit, the suck-back of patients' saliva into the line due to the lack of adequate valves, and contamination from bottled water systems. Some of the main determinants of microbial contamination in DUWLs are: a very small lumen size (0.5-2 mm) of the tubing used, high surface-to-volume ratio (6:1), low throughput and the materials of which the tubing is made, water stagnation outside of working hours. The environmental conditions present inside the conduits of the dental unit may facilitate the proliferation of micro-organisms and the consequent formation of biofilm on the interior surface of the pipes of DUWLs. During the use of handpieces, particularly high-speed rotating instruments, a spray is thrown up in the form of aerosols or spatters containing biological material (saliva, blood and dental plaque) and micro-organisms. This means that the health of both dental staff and patients could be at risk of infection. The risk of cross-infections in dental settings can be tackled by implementing combined interventions to prevent the contamination of DUWLs.

Demystifying the mist: Sources of microbial bioload in dental aerosols

The risk of transmitting airborne pathogens is an important consideration in dentistry and has acquired special significance in the context of recent respiratory disease epidemics. The purpose of this review, therefore, is to examine (1) what is currently known regarding the physics of aerosol creation, (2) the types of environmental contaminants generated by dental procedures, (3) the nature, quantity, and sources of microbiota in these contaminants and (4) the risk of disease transmission from patients to dental healthcare workers. Most dental procedures that use ultrasonics, handpieces, air‐water syringes, and lasers generate sprays, a fraction of which are aerosolized. The vast heterogeneity in the types of airborne samples collected (spatter, settled aerosol, or harvested air), the presence and type of at‐source aerosol reduction methods (high‐volume evacuators, low volume suction, or none), the methods of microbial sampling (petri dishes with solid media, filter paper discs, air harvesters, and liquid transport media) and assessment of microbial bioload (growth conditions, time of growth, specificity of microbial characterization) are barriers to drawing robust conclusions. For example, although several studies have reported the presence of microorganisms in aerosols generated by ultrasonic scalers and high‐speed turbines, the specific types of organisms or their source is not as well studied. This paucity of data does not allow for definitive conclusions to be drawn regarding saliva as a major source of airborne microorganisms during aerosol generating dental procedures. Well‐controlled, large‐scale, multi center studies using atraumatic air harvesters, open‐ended methods for microbial characterization and integrated data modeling are urgently needed to characterize the microbial constituents of aerosols created during dental procedures and to estimate time and extent of spread of these infectious agents.

Treatments for preventing recurrence of infection with Pseudomonas aeruginosa in people with cystic fibrosis

BACKGROUND

Chronic infection with Pseudomonas aeruginosa (PA) in cystic fibrosis (CF) is a source of much morbidity and mortality. Eradication of early PA infection is possible, but can recur in many individuals. We sought to examine strategies to delay the time to PA recurrence in people with CF.

OBJECTIVES

To establish whether secondary prevention strategies, using antibiotics or other therapies, increase the chances of people with CF remaining free from PA infection following successful eradication therapy.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched ongoing trials registries and the reference lists of relevant articles and reviews. Date of last search: 21 August 2019.

SELECTION CRITERIA

Randomised controlled trials (and quasi-randomised trials where the risk of bias was low) comparing any treatment modality aimed at preventing recurrence of PA infection with placebo, standard therapy or any other treatment modality in people with CF who have undergone successful eradication of PA.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and risk of bias. Quality of the evidence was assessed using GRADE. Conflicts were resolved by discussion and the opinion of a third review author was sought where necessary. Only a subset of participants in the included trial were eligible, therefore individual participant data were requested and obtained from the trial investigators.

MAIN RESULTS

We included one trial (n = 306) in the review; however, only 253 participants had undergone successful eradication of PA, so fulfilling the inclusion criteria for our review. Information presented relates only to the included subset of participants. The trial recruited children aged one to 12 years (mean (standard deviation (SD)) age of 5.8 (3.5) years), 129 participants (51.0%) were female and the median follow-up was 494 days. We compared cycled therapy with tobramycin inhalation solution (TIS), in which participants underwent 28 days of TIS every three months, with culture-based therapy, in which participants were only prescribed medication when a quarterly sputum sample was positive for PA. Reasons for downgrading the quality of the evidence included applicability (only included children), incomplete outcome data and a small number of participants. The time to next isolation of PA was probably shorter with cycled TIS therapy than with culture-based therapy, hazard ratio (HR) 2.04 days (95% confidence interval (CI) 1.28 to 3.26) (moderate-quality evidence). This is in contrast to the main publication of the only included trial, which examined rate of PA positivity rather than time to PA infection and included participants not eligible for inclusion in this review. At the end of the trial, there was no difference between the cycled and culture-based groups in the change from baseline in forced expiratory volume in one second (FEV₁) L, mean difference (MD) 0.0 L (95% CI -0.09 to 0.09) or in FEV₁ % predicted, MD 0.70% (95% CI -4.33 to 5.73) (both very low-quality evidence). There was no difference in the change from baseline for FVC between the groups. There was also no difference in the frequency of pulmonary exacerbations between groups, MD -0.18 (95% CI -0.51 to 0.14) (moderate-quality evidence). Similarly, there was no difference between groups in the risk of participants developing novel resistant bacteria, RR 1.00 (95% CI 0.67 to 1.5) (moderate-quality evidence). There were more severe adverse events in the cycled group, but the type of treatment probably makes little or no difference to the results, RR 0.65 (95% CI 0.39 to 1.11) (moderate-quality evidence). There was no difference between groups in the change in weight or height from baseline or in rates of adherence to tobramycin or all trial medicines. The included trial did not assess changes in quality of life, the time to chronic infection with PA or the cost-effectiveness of treatment.

AUTHORS' CONCLUSIONS

Cycled TIS therapy may be beneficial in prolonging the time to recurrence of PA after successful eradication, but further trials are required, specifically addressing this question and in both adults and children.

Cross-transmission in the Dental Office: Does This Make You Ill?

PURPOSE OF REVIEW

Recently, numerous scientific publications were published which shed new light on the possible risks of infection for dental healthcare workers and their patients. This review aimed to provide the latest insights in the relative risks of transmission of (pathogenic) micro-organisms in the dental office.

RECENT FINDINGS

Of all different routes of micro-organism transmission during or immediately after dental treatment (via direct contact/via blood-blood contact/via dental unit water and aerosols), evidence of transmission is available. However, the recent results put the risks in perspective; infections related to the dental office are most likely when infection control measures are not followed meticulously.

SUMMARY

The risk for transmission of pathogens in a dental office resulting in an infectious disease is still unknown; it seems to be limited in developed countries but it cannot be considered negligible. Therefore, maintaining high standards of infection preventive measures is of high importance for dental healthcare workers to avoid infectious diseases due to cross-contamination.

Overcoming the problem of residual microbial contamination in dental suction units left by conventional disinfection using novel single component suction handpieces in combination with automated flood disinfection

OBJECTIVES

Decontaminating dental chair unit (DCU) suction systems in a convenient, safe and effective manner is problematic. This study aimed to identify and quantify the extent of the problems using 25 DCUs, methodically eliminate these problems and develop an efficient approach for reliable, effective, automated disinfection.

METHODS

DCU suction system residual contamination by environmental and human-derived bacteria was evaluated by microbiological culture following standard aspiration disinfection with a quaternary ammonium disinfectant or alternatively, a novel flooding approach to disinfection. Disinfection of multicomponent suction handpieces, assembled and disassembled, was also studied. A prototype manual and a novel automated Suction Tube Cleaning System (STCS) were developed and tested, as were novel single component suction handpieces.

RESULTS

Standard aspiration disinfection consistently failed to decontaminate DCU suction systems effectively. Semi-confluent bacterial growth (101-500 colony forming units (CFU) per culture plate) was recovered from up to 60% of suction filter housings and from up to 19% of high and 37% of low volume suction hoses. Manual and automated flood disinfection of DCU suction systems reduced this dramatically (ranges for filter cage and high and low volume hoses of 0-22, 0-16 and 0-14CFU/plate, respectively) (P<0.0001). Multicomponent suction handpieces could not be adequately disinfected without prior removal and disassembly. Novel single component handpieces, allowed their effective disinfection in situ using the STCS, which virtually eliminated contamination from the entire suction system.

CONCLUSION

Flood disinfection of DCU suction systems and single component handpieces radically improves disinfection efficacy and considerably reduces potential cross-infection and cross-contamination risks.

CLINICAL SIGNIFICANCE

DCU suction systems become heavily contaminated during use. Conventional disinfection does not adequately control this. Furthermore, multicomponent suction handpieces cannot be adequately disinfected without disassembly, which is costly in time, staff and resources. The automated STCS DCU suction disinfection system used with single component handpieces provides an effective solution.

Pseudomonas aeruginosa Acquisition in Cystic Fibrosis Patients in Context of Otorhinolaryngological Surgery or Dentist Attendance: Case Series and Discussion of Preventive Concepts

Introduction. P. aeruginosa is the primary cause for pulmonary destruction and premature death in cystic fibrosis (CF). Therefore, prevention of airway colonization with the pathogen, ubiquitously present in water, is essential. Infection of CF patients with P. aeruginosa after dentist treatment was proven and dental unit waterlines were identified as source, suggesting prophylactic measures. For their almost regular sinonasal involvement, CF patients often require otorhinolaryngological (ORL) attendance. Despite some fields around ORL-procedures with comparable risk for acquisition of P. aeruginosa, such CF cases have not yet been reported. We present four CF patients, who primarily acquired P. aeruginosa around ORL surgery, and one around dentist treatment. Additionally, we discuss risks and preventive strategies for CF patients undergoing ORL-treatment. Perils include contact to pathogen-carriers in waiting rooms, instrumentation, suction, drilling, and flushing fluid, when droplets containing pathogens can be nebulized. Postsurgery mucosal damage and debridement impair sinonasal mucociliary clearance, facilitating pathogen proliferation and infestation. Therefore, sinonasal surgery and dentist treatment of CF patients without chronic P. aeruginosa colonization must be linked to repeated microbiological assessment. Further studies must elaborate whether all CF patients undergoing ORL-surgery require antipseudomonal prophylaxis, including nasal lavages containing antibiotics. Altogether, this underestimated risk requires structured prevention protocols.

Healthcare-associated viral and bacterial infections in dentistry

Infection prevention in dentistry is an important topic that has gained more interest in recent years and guidelines for the prevention of cross-transmission are common practice in many countries. However, little is known about the real risks of cross-transmission, specifically in the dental healthcare setting. This paper evaluated the literature to determine the risk of cross-transmission and infection of viruses and bacteria that are of particular relevance in the dental practice environment. Facts from the literature on HSV, VZV, HIV, Hepatitis B, C and D viruses, Mycobacterium spp., Pseudomonas spp., Legionella spp. and multi-resistant bacteria are presented. There is evidence that Hepatitis B virus is a real threat for cross-infection in dentistry. Data for the transmission of, and infection with, other viruses or bacteria in dental practice are scarce. However, a number of cases are probably not acknowledged by patients, healthcare workers and authorities. Furthermore, cross-transmission in dentistry is under-reported in the literature. For the above reasons, the real risks of cross-transmission are likely to be higher. There is therefore a need for prospective longitudinal research in this area, to determine the real risks of cross-infection in dentistry. This will assist the adoption of effective hygiene procedures in dental practice.

Improved early diagnosis of Pseudomonas aeruginosa by real-time PCR to prevent chronic colonisation in a paediatric cystic fibrosis population

Early detection of Pseudomonas aeruginosa in children with cystic fibrosis is hampered by the need to process a sub-optimal specimen type, namely cough swabs, which are known to have a lower positive yield than sputa or more invasive samples. This delay in the detection of low levels of P. aeruginosa could potentially result in the loss of an opportunity to initiate early aggressive antibiotic therapy and result in chronic colonisation, with a poorer overall prognosis. Quantitative real-time PCR (qPCR) offers an opportunity to increase the detection rate of P. aeruginosa compared to traditional culture techniques. This study examined 500 cough swabs and 42 sputum samples from paediatric patients and showed that detection of P. aeruginosa could be increased in both sample types by 100% and 45% respectively. Overall the sensitivity was 100% and specificity of 58% when compared to culture as a gold standard. These results although initially promising require careful consideration both from a treatment and infection control standpoint as the significance of detection of very low levels of P. aeruginosa is unclear.

Challenging and emerging pathogens in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterised by chronic inflammation and infection. Patients are predominantly infected by specific pathogens, of which Staphylococcus aureus and Pseudomonas aeruginosa are the most important. In recent years however there has been an increasing number of reports on potentially emerging and challenging pathogens like Stenotrophomonas maltophilia, Non-tuberculous mycobacteria, highly prevalent P. aeruginosa clones, methicillin resistant Staphylococcus aureus and Burkholderia cepacia. Also, a role for viral infections in the pathogenesis of CF lung disease has increasingly been recognised. It is not always clear whether or how these pathogens influence the progression of CF lung disease and how they should be treated. In this review, the epidemiology and clinical impact of these pathogens is discussed. Furthermore, treatment strategies of these pathogens in a CF setting are reviewed.

Eradication of early Pseudomonas infection in cystic fibrosis

Chronic infection with the environmental bacterium Pseudomonas aeruginosa is associated with greater morbidity and mortality for people with cystic fibrosis. Strict infection control measures including segregation appear to reduce but not eliminate the risk of initial acquisition of the organism. There is now good evidence from randomized controlled trials that early eradication regimens consisting of anti-pseudomonal antibiotics are effective in clearing P. aeruginosa and delaying the development of chronic infection in the majority of subjects. These regimens are safe and cost-effective. Ensuring that such regimens are widely adopted is therefore of considerable importance to improving outcomes for people with cystic fibrosis. The most effective antibiotic regimen, and the effects of new nebulizer technologies and methods to improve concordance remain to be determined.

Pseudomonas aeruginosa diversity in distinct paediatric patient groups

Pseudomonas aeruginosa is a pathogen that often infects patients who are either immunocompromised or have local defects in host defences. It is known that cystic fibrosis (CF) patients are sometimes infected with certain clonal isolates. It is not clear whether these clonal isolates also infect non-CF patients and whether clonality of isolates occurs in other patient groups. The aim of this study was to investigate P. aeruginosa diversity and the occurrence of clones within five distinct paediatric patient groups susceptible to P. aeruginosa infection. P. aeruginosa isolates were cultured from 157 patients (CF first infection (CF-1 group) (29); CF chronic infection (CF-chronic group) (27); urinary tract infection (34); chronic suppurative otitis media (43); and intensive-care hospitalization/immunodeficiency (24)). All 202 phenotypically different isolates were tested for antimicrobial resistance and further typed by pulsed-field gel electrophoresis. Simpson's diversity index was calculated for the five groups. CF-chronic patients carried the highest number of distinct P. aeruginosa phenotypes and genotypes per culture. Isolates from the CF-chronic group were significantly less diverse than those from the other groups. A group of clonal isolates was observed among patients from the CF-chronic and CF-1 groups. These or different clonal isolates were not encountered among the three other patient groups. No characteristic resistance pattern could be identified among isolates from the distinct patient groups and among the clonal isolates. In conclusion, isolates of the CF-chronic group were less diverse than those in the other patient groups with P. aeruginosa infection; clonal isolates were not encountered in non-CF patients. Transmission of clonal CF isolates to other patient groups was not observed.

Do contaminated dental unit waterlines pose a risk of infection?

OBJECTIVES

To review the evidence that the dental unit waterlines are a source of occupational and healthcare acquired infection in the dental surgery.

DATA

Transmission of infection from contaminated dental unit waterlines (DUWL) is by aerosol droplet inhalation or rarely imbibing or wound contamination in susceptible individuals. Most of the organisms isolated from DUWL are of low pathogenicity. However, data from a small number of studies described infection or colonisation in susceptible hosts with Legionella spp., Pseudomonas spp. and environmental mycobacteria isolated from DUWL. The reported prevalence of legionellae in DUWL varies widely from 0 to 68%. The risk from prolonged occupational exposure to legionellae has been evaluated. Earlier studies measuring surrogate evidence of exposure to legionellae in dental personnel found a significant increase in legionella antibody levels but in recent multicentre studies undertaken in primary dental care legionellae were isolated at very low rate and the corresponding serological titres were not above background levels. Whereas, a case of fatal Legionellosis in a dental surgeon concluded that the DUWL was the likely source of the infection. The dominant species isolated from dental unit waterlines (DUWL) are Gram-negative bacteria, which are a potent source of cell wall endotoxin. A consequence of indoor endotoxin exposure is the triggering or exacerbation of asthma. Data from a single large practice-based cross-sectional study reported a temporal association between occupational exposure to contaminated DUWL with aerobic counts of >200cfu/mL at 37 degrees C and development of asthma in the sub-group of dentists in whom asthma arose following the commencement of dental training.

SOURCES

Medline 1966 to February 2007 was used to identify studies for this paper.

STUDY SELECTION

Design criteria included randomised control trials, cohort, and observational studies in English.

CONCLUSIONS

Although the number of published cases of infection or respiratory symptoms resulting from exposure to water from contaminated DUWL is limited, there is a medico-legal requirement to comply with potable water standards and to conform to public perceptions on water safety.

Infection Control Practice in Cystic Fibrosis Centers

In this article, the authors outline some of the major historical events that signaled the need to better understand mechanisms of infection in cystic fibrosis (CF). The authors discuss general principles of infection control, focusing on issues of particular importance to patients who have CF. The authors also describe the major pathogens associated with the CF airway, provide a review of findings from inpatient and outpatient studies of infection control, and provide an outline of future directions for investigation.

Molecular epidemiology and dynamics of Pseudomonas aeruginosa populations in lungs of cystic fibrosis patients

The ability to establish lifelong persistent infections is a fundamental aspect of the interactions between many pathogenic microorganisms and their mammalian hosts. One example is chronic lung infections by the opportunistic pathogen Pseudomonas aeruginosa in cystic fibrosis (CF) patients. This infection process is associated with extensive genetic adaptation and microevolution of the infecting bacteria. Through investigations of P. aeruginosa populations and infection dynamics in a group of CF patients followed at the Danish CF Clinic in Copenhagen, we have identified two distinct and dominant clones that have evolved into highly successful colonizers of CF patient airways. A significant component of the evolutionary success of these two clones has been their efficient transmissibility among the CF patients. The two clones have been present and transmitted among different CF patients for more than 2 decades. Our data also suggest that the P. aeruginosa population structure in the CF patient airways has been influenced by competition between different clones and that the two dominant clones have been particularly competitive within the lungs, which may add to their overall establishment success. In contrast, we show that adaptive traits commonly associated with establishment of chronic P. aeruginosa infections of CF patients, such as transition to the mucoid phenotype and production of virulence factors, play minor roles in the ability of the two dominant clones to spread among patients and cause long-term chronic infections. These findings suggest that hitherto-unrecognized evolutionary pathways may be involved in the development of successful and persistent P. aeruginosa colonizers of CF patient lungs.

The effect of ultrafiltration on the quality of water from dental units

AIM

The purpose of the present study was to evaluate the effect of an ultrafiltration system on the bacteriological water quality in dental units.

DESIGN

A BIN-X UF-45R ultrafiltration system with a pore membrane of 0.03 microm was mounted at the water supply of six older dental units while six control units were disinfected with sodium hypochlorite according to a standard procedure. As the water quality in the test units deteriorated in spite of ultrafiltration the test units were subjected to chlorination at different concentrations several times during the test period.

OUTCOME MEASURE

The number of colony forming units (cfu)/ml in water was determined according to European Standards on water quality.

RESULTS

While the median number of cfu/ml in control units never exceeded 7.6x10(1) the median cfu/ml in test units increased up to >1x10(5) in 3-4 days every time chlorination of the units was interrupted.

CONCLUSION

The ultrafiltration system mounted at the water supply for six dental units was not able to control the bacteria originating from the existing biofilm in the water lines and deliver water of an acceptable quality.

Measuring the validity of two in-office water test kits

BACKGROUND

The authors conducted a study to determine the validity of two commercially available in-office water test kits compared with a spread plate technique using the gold standard dehydrated culture medium R2A agar for monitoring the quality of dental treatment water.

METHODS

Over a 12-week period, one author monitored nine dental units in a dental school that each were equipped with an independent water reservoir. The author collected 351 split samples, cultured them using three test methods, counted bacterial colonies manually and assessed validity using two cutoff values: < or = 200 colony-forming units per milliliter (CFU/mL) (an American Dental Association goal) and < or = 500 CFU/mL (a Centers for Disease Control and Prevention [CDC] recommendation and a U.S. Environmental Protection Agency [EPA] mandate).

RESULTS

Of the 351 split samples processed, the in-office test kits' accuracy ranged from 25 to 69 percent, according to the ADA and CDC/EPA recommendations, compared with the R2A agar.

CONCLUSIONS

Overall, the in-office test kits underestimated bacteria levels, producing inaccurate measurements of bacterial levels compared with the R2A agar.

CLINICAL IMPLICATIONS

The data suggest that use of the two in-office test kits could result in a lack of compliance, owing to underestimating bacterial contamination with recognized recommendations for dental unit waterline quality.

Early intervention and prevention of lung disease in cystic fibrosis: a European consensus

In patients with cystic fibrosis (CF), early intervention and prevention of lung disease is of paramount importance. Principles to achieve this aim include early diagnosis of CF, regular monitoring of the clinical status, various hygienic measures to prevent infection and cross-infection, early use of antibiotic courses in patients with recurrent or continuous bacterial colonisation and appropriate use of chest physiotherapy.

Infection control in cystic fibrosis

Over the past 20 years there has been a greater interest in infection control in cystic fibrosis (CF) as patient-to-patient transmission of pathogens has been increasingly demonstrated in this unique patient population. The CF Foundation sponsored a consensus conference to craft recommendations for infection control practices for CF care providers. This review provides a summary of the literature addressing infection control in CF. Burkholderia cepacia complex, Pseudomonas aeruginosa, and Staphylococcus aureus have all been shown to spread between patients with CF. Standard precautions, transmission-based precautions including contact and droplet precautions, appropriate hand hygiene for health care workers, patients, and their families, and care of respiratory tract equipment to prevent the transmission of infectious agents serve as the foundations of infection control and prevent the acquisition of potential pathogens by patients with CF. The respiratory secretions of all CF patients potentially harbor clinically and epidemiologically important microorganisms, even if they have not yet been detected in cultures from the respiratory tract. CF patients should be educated to contain their secretions and maintain a distance of >3 ft from other CF patients to avoid the transmission of potential pathogens, even if culture results are unavailable or negative. To prevent the acquisition of pathogens from respiratory therapy equipment used in health care settings as well as in the home, such equipment should be cleaned and disinfected. It will be critical to measure the dissemination, implementation, and potential impact of these guidelines to monitor changes in practice and reduction in infections.

The effect of Sterilex Ultra for disinfection of dental unit waterlines

AIM

To evaluate the effect of a disinfectant agent based on hydrogen peroxide (Sterilex Ultra, Sterilex Corporation, Maryland, USA) on the microbiological water quality in dental unit waterlines (DUWL).

SETTING

Six older dental units were disinfected with Sterilex Ultra and another six units with sodium hypochlorite. The results were compared to six non-disinfected units examined during a period without patient treatment.

OUTCOME MEASURE

The number of colony forming units of bacteria (cfu)/ml of water was determined according to European Standards on water quality.

DESIGN

The water quality was initially determined during a six week period, and subsequently in more detail for two weeks. Finally, the effect of prolonged administration of Sterilex Ultra was investigated for six weeks.

RESULTS

Instillation of Sterilex Ultra according to the recommendations of the manufacturer initially reduced the number of bacteria in DUWL to <10(2) cfu/ml. However, following daily, as well as prolonged administration of Sterilex Ultra a gradual recolonisation was observed resulting in bacterial numbers >10(4) cfu/ml in a number of units. Major differences between the number of cfu/ml in individual units were observed.

CONCLUSION

Neither daily nor extended administration of Sterilex Ultra was capable of maintaining an acceptable water quality in these older dental units.

Waterborne pathogens and dental waterlines

Humans, like every other living thing on Earth, have evolved in a world dominated by many billions of microscopic life forms. Most of the time, we live in a state of harmony (or even mutualism) with our invisible coinhabitants. When this balance becomes disturbed however, the consequences can be devastating. Infectious diseases including malaria, tuberculosis, and AIDS remain the world's greatest mass murderers. Dental workers strive to reduce infection risks for their patients through infection control measures that reduce or eliminate potentially pathogenic agents in the clinical environment. As increasing numbers of patients with varying degrees of immune suppression present for dental treatment, the need to ensure an aseptic treatment environment will become a higher priority for the dental profession. The possibility that exposure to aerosols contaminated with endotoxin might exacerbate asthma or cause chronic respiratory problems in dental health care workers should be investigated. Although direct evidence of widespread complications among patients or occupationally acquired illness among dental workers is presently lacking, reducing the numbers of microorganisms present in dental treatment water is consistent with other empiric measures that form the basis of infection-control practice.

Infection control recommendations for patients with cystic fibrosis: microbiology, important pathogens, and infection control practices to prevent patient-to-patient transmission

Infection Control Recommendations for Patients With Cystic Fibrosis: Microbiology, Important Pathogens, and Infection Control Practices to Prevent Patient-to-Patient Transmissionupdates, expands, and replaces the consensus statement,Microbiology and Infectious Disease in Cystic Fibrosispublished in 1994. This consensus document presents background data and evidence-based recommendations for practices that are intended to decrease the risk of transmission of respiratory pathogens among CF patients from contaminated respiratory therapy equipment or the contaminated environment and thereby reduce the burden of respiratory illness. Included are recommendations applicable in the acute care hospital, ambulatory, home care, and selected non-healthcare settings. The target audience includes all healthcare workers who provide care to CF patients. Antimicrobial management is beyond the scope of this document.

Risk assessment of dental unit waterline contamination

Biofilms form rapidly on dental unit waterlines. The majority of the organisms in the biofilm are harmless environmental species, but some dental units may harbour opportunistic respiratory pathogens. This paper describes a risk assessment approach to analysing the hazard from biofilm organisms contaminating dental unit waterlines on the respiratory health of both the dental team and patients. The health risk from the respiratory pathogens Legionella spp, Mycobacterium spp and Pseudomonads was found to be low. Nevertheless, in order to satisfy water regulations and comply with health and safety legislation dentists should institute infection-control measures to maintain the dental unit water at the standard of less than 200 colony-forming units per ml of aerobic bacteria.

The effect of drying dental unit waterline biofilms on the bacterial load of dental unit water

AIM

To evaluate drying of the dental unit waterlines (DUWL) as a new method of controlling the bacterial biofilm therein and thereby to reduce the number of living bacteria in dental unit water.

SETTING

18 dental units were incorporated into the study. Six units constituted the experimental units, which were emptied for stagnant water in the DUWL every night; six units were chlorinated every night (positive controls), and six units were left untreated (negative controls).

OUTCOME MEASURE

Water samples from the ultrasonic scaler were examined microbiologically according to the guidelines from the Danish Standard Association and the number of colony forming units (cfu) per ml of water was determined.

RESULT

Drying of DUWL did not reduce the number of cfu per ml in dental unit water below the levels found in DUWL left untreated.

CONCLUSION

The drying of the waterlines for about 16 hours per day during a 19-day period did not result in reduced counts of bacteria in water samples from the experimental units.

Typing of Pseudomonas aeruginosa strains in Norwegian cystic fibrosis patients

OBJECTIVES

Typing of Pseudomonas aeruginosa isolates from Norwegian cystic fibrosis (CF) patients with chronic Pseudomonas lung infection in order to see whether cross-infection might have occurred.

METHODS

Isolates from 60 patients were collected during the years 1994-98, and typed by pulsed field gel electrophoresis.

RESULTS

Seventy-one strains were identified. One large cluster of identical strains included 27 patients, and 13 smaller clusters of 2-4 patients were found (26 patients). Seven patients had a strain not shared by other patients (private strains). Harboring the main cluster strain was significantly associated with participation in summer camps and training courses (P = 0.004, chi-squared test). There were no associations with regular admissions to hospital (intravenous antibiotic courses) or smaller social gatherings of short duration. Small clusters and private strains were not associated with any of the risk factors. All strains were sensitive to colistin. The minimal inhibitory concentrations were generally lower in Norwegian P. aeruginosa strains compared with isolates from Danish patients.

CONCLUSIONS

Our results indicate that cross-infection with P. aeruginosa between cystic fibrosis patients has occurred.

Prospects for the prevention and control of pseudomonal infection in children with cystic fibrosis

Most patients with cystic fibrosis (CF) experience recurrent and chronic endobronchial Pseudomonas aeruginosa infections. It is possible to prevent or delay the onset of these chronic infections in most patients with CF by eliminating cross-infection and by early aggressive antibiotic treatment of the first positive sputum culture and of subsequent intermittent colonisation. Lung tissue damage is caused by activation of the immunologically specific inflammatory defence mechanisms of the lungs, which are initiated by the antibody response and dominated by polymorphonuclear neutrophil leucocytes and their proteolytic and oxidative products. This inflammation induces a phenotypic shift from nonmucoid to mucoid, alginate-producing phenotypes of P. aeruginosa which then grow, endobronchially, as a biofilm. Such biofilms are impossible to eradicate with antibiotics. By using chronic suppressive antibiotic maintenance therapy and anti-inflammatory drugs it is however, possible to maintain the lung function of these patients for a number of years.

The dental unit waterline controversy: defusing the myths, defining the solutions

BACKGROUND AND OVERVIEW

This article reviews the literature on the subject of dental unit waterline contamination. It has been expanded from the text of a lecture given at the Scientific Frontiers in Dentistry program sponsored by the National Institute for Dental and Craniofacial Research in Bethesda, Md., in July 1999. The author examines the underlying biological causes of waterline colonization by microorganisms, the evidence of potential health consequences and possible means of improving the quality of dental water. He also describes examples of devices currently marketed to improve and maintain the quality of dental treatment water.

CONCLUSIONS

Microorganisms colonize dental units and contaminate dental treatment water. While documented instances of related illness are few, water that does not meet potable-water standards is inappropriate for use in dentistry.

CLINICAL IMPLICATIONS

Exposure to water containing high numbers of bacteria violates basic principles of clinical infection control. Dentists should consider available options for improving the quality of water used in dental treatment.

Changing epidemiology of Pseudomonas aeruginosa infection in Danish cystic fibrosis patients (1974-1995)

Recurrent and chronic lower airway infection with Pseudomonas aeruginosa (PA) is an important component of cystic fibrosis (CF) pulmonary disease. Different modes of treatment and control of CF patients have been introduced at the Copenhagen CF Centre over the past 20 years and have been associated with improved survival. Treatment consisted of: 1) elective antibiotics for 14 days every 3 months to patients with chronic PA infection (started in 1976), 2) cohort isolation to prevent cross-infection (patients with PA were separated from patients without PA, starting in 1981); and 3) early intensive treatment with inhaled colistin and oral ciprofloxacin from time of initial PA colonization (started in 1989). The aim of the present study was to evaluate the impact of each of these interventions on the changes in the epidemiology of PA. Based on monthly cultures of lower airway secretions in each CF patient seen during 1974-1995, significant changes in the incidence and prevalence of the PA infection were found. The monthly prevalence of chronic PA increased significantly (P < 0.0001) from below 40% before 1976 to above 60% in 1980, which was found to be due to cross-infection among the CF patients after introduction of elective antibiotic courses in 1976. To deal with this problem, cohort isolation was introduced in 1981, and since then the monthly point prevalence of chronic PA decreased slowly until 1989 (P < 0.0001), when early intensive treatment from initial PA colonization was introduced; this was associated with a further decrease in point prevalence to 45% in 1995 (P < 0.005). The annual incidence of chronic PA infection also decreased significantly (P < 0.01) from 16% to below 2% after introduction of cohort isolation and early intensive treatment from initial PA isolation. Furthermore, the time from acquisition of first PA to development of chronic PA infection increased significantly, from approximately 1 year to almost 4 years after introduction of cohort isolation (P < 0.0001). After introduction of early intensive treatment, the probability of still not having developed chronic PA infection 7 years after the first isolation of PA was above 80% (P < 0.0001). In conclusion, the introduction of cohort isolation and early intensive treatment following the initial isolation of PA resulted in a reduced incidence and prevalence of chronic PA infection. We are not aware of other studies showing a decreasing prevalence of chronic PA infection, as survival of CF patients has increased.

Effect of steam sterilization inside the turbine chambers of dental turbines

OBJECTIVE

It has been demonstrated that contamination of the insides of high-speed dental turbines occurs and that bacteria as well as viruses may remain infectious when expelled from such turbines during subsequent use. Consequently, it has been widely recommended that a high-speed turbine be sterilized after each patient. The purpose of this study was to evaluate the effect of steam autoclaving on a high-speed dental turbine with a contaminated turbine chamber.

STUDY DESIGN

Streptococcus salivarius and endospores of Bacillus stearothermophilus were used as test organisms to determine the effectiveness of 4 different small non-vacuum autoclaves and one vacuum autoclave.

RESULTS

The study demonstrated different efficiencies among the small non-vacuum autoclaves, the best showing close to a 6 log reduction of the test organisms inside the turbine chamber. When cleaning and lubrication of the high-speed dental turbine was carried out before autoclaving, this level of reduction was observed for all the examined non-vacuum autoclaves.

CONCLUSIONS

It is concluded that cleaning before sterilization is essential for safe use of high-speed dental turbines and that small non-vacuum autoclaves should be carefully evaluated before being used for the reprocessing of hollow instruments such as high-speed turbines.