Statistical modeling of dental unit water bacterial test kit performance.
OBJECTIVE
While it is important to monitor dental water quality, it is unclear whether in-office test kits provide bacterial counts comparable to the gold standard method (R2A). Studies were conducted on specimens with known bacterial concentrations, and from dental units, to evaluate test kit accuracy across a range of bacterial types and loads.


METHODS
Colony forming units (CFU) were counted for samples from each source, using R2A and two types of test kits, and conformity to Poisson distribution expectations was evaluated. Poisson regression was used to test for effects of source and device, and to estimate rate ratios for kits relative to R2A.


RESULTS
For all devices, distributions were Poisson for low CFU/mL when only beige-pigmented bacteria were considered. For higher counts, R2A remained Poisson, but kits exhibited over-dispersion. Both kits undercounted relative to R2A, but the degree of undercounting was reasonably stable. Kits did not grow pink-pigmented bacteria from dental-unit water identified as Methylobacterium rhodesianum.


CONCLUSIONS
Only one of the test kits provided results with adequate reliability at higher bacterial concentrations. Undercount bias could be estimated for this device and used to adjust test kit results. Insensitivity to methylobacteria spp. is problematic.
Cohen
Mark E
ME
Naval Institute for Dental and Biomedical Research Great Lakes, IL, USA. mark.cohen@med.navy.mil
Harte
Jennifer A
JA
Stone
Mark E
ME
O'Connor
Karen H
KH
Coen
Michael L
ML
Cullum
Malford E
ME
D015169:Colony Count, Microbial; D003748:Dental Equipment; D004866:Equipment Contamination; D019552:Infection Control, Dental / Q000379:methods*; D016013:Likelihood Functions; D008826:Microbial Sensitivity Tests; D015233:Models, Statistical; D016012:Poisson Distribution; D012044:Regression Analysis; D014871:Water Microbiology