title: Evaluation of the potential risk of occupational asthma in dentists exposed to contaminated dental unit waterlines.
abstract: BACKGROUND
  Most of the organisms isolated from dental unit waterlines (DUWL) are Gram-negative bacteria, which contain cell wall endotoxin. A consequence of endotoxin exposure is the exacerbation of asthma.
  
  
  OBJECTIVE
  This study examined the prevalence and onset of asthma among dentists and determined whether or not these were associated with the microbiological quality of DUWL in their practices.
  
  
  METHODS
  266 randomly selected dentists (100 from rural Northern Ireland, 166 from London) completed a health questionnaire, which included questions on prevalence and time of onset of asthma. Water samples taken from the dental handpieces and surgery washbasin cold taps in all the practices were analysed using standard techniques. The questionnaire data were evaluated using both single and multivariable logistic regression. The variables considered were: smoking; surgery location; time treating patients per week; DUWL counts of Pseudomonas aeruginosa, total Pseudomonas spp., fungi, Mycobacterium spp., total aerobic colony counts (ACC) at 22 degrees C and 37 degrees C.
  
  
  RESULTS
  There was no significant association between any of the variables tested in dentists and a history of asthma. A subgroup analysis was performed on dentists (n=33) who reported developing asthma since they started dental training. The final multivariable model indicated that passive smoking (OR 0.08, 95% CI 0.01-0.87, P=0.038) and total aerobic counts of >200 cfu/ml at 37 degrees C (OR 6.72, 95% CI 1.15-39.24, P=0.034) were significant variables for developing asthma since starting training as a dentist. ACC were significantly higher in London (P<0.0001) and London dentists were more likely to have developed asthma since they started training than their Northern Ireland counterparts (OR 4.4, 95% CI 1.09-17.72, P=0.033).
  
  
  CONCLUSIONS
  This study suggests that the temporal onset of asthma may be associated with occupational exposure to contaminated DUWL among dentists in London and Northern Ireland.
authors.affiliation: Unit of Distance Education, GKT Dental Institute, King's College London, UK. caroline@lpankhurst.freeserve.co.uk
authors.forename: Caroline L
authors.initials: CL
authors.lastname: Pankhurst
authors.forename: Wilson
authors.initials: W
authors.lastname: Coulter
authors.forename: John N
authors.initials: JN
authors.lastname: Philpott-Howard
authors.forename: Susanne
authors.initials: S
authors.lastname: Surman-Lee
authors.forename: Fiona
authors.initials: F
authors.lastname: Warburton
authors.forename: Stephen
authors.initials: S
authors.lastname: Challacombe
mesh_terms: D000704:Analysis of Variance; D001249:Asthma / Q000382:microbiology*; D001420:Bacteria, Aerobic / Q000302:isolation & purification / Q000472:pathogenicity; D016009:Chi-Square Distribution; D015169:Colony Count, Microbial; D003430:Cross-Sectional Studies; D003748:Dental Equipment / Q000009:adverse effects*; D003813:Dentistry; D005658:Fungi / Q000472:pathogenicity; D006090:Gram-Negative Bacteria / Q000302:isolation & purification / Q000472:pathogenicity; D006801:Humans; D008131:London; D009660:Northern Ireland; D009784:Occupational Diseases / Q000382:microbiology*; D016273:Occupational Exposure; D011795:Surveys and Questionnaires; D014871:Water Microbiology