This study set out to ascertain the sensitivity of the Dip Slide™ test when used to test dental unit waterlines (DUWLs) and investigate if the sensitivity could be optimised without compromising the specificity.
Method:
Water samples from 27 DUWLs in general dental practices were taken during the working day and cultured for 2 days using the Dip Slide™ test as per manufacturer’s instructions and for an extended incubation period of 5 days under laboratory conditions. The samples were also cultured using the industry standard R2A agar laboratory test.
Result:
Following two days incubation at the dental practice, results indicated the sensitivity of the Dip Slide™ at the lowest value specified by the manufacturers of 1000 cfu/ml level was 66% and specificity 83%. When cultured for 5 days at 30°C, the sensitivity, 95%, and specificity, 85%, increased further. Using an unmeasured volume of inoculum or 100µl made little difference as did a constant or ambient temperature. The R2A test showed that 85% of surgeries exceeded the contamination level set by the Department of Health (DoH) of 100-200 cfu/ml.
Conclusion:
This study confirms that longer incubation time increases the sensitivity without compromising the specificity of the Dip Slide™ test. It is applicable for monitoring general levels of planktonic bacteria in water systems and can be used to detect gross contamination of dental waterlines if used over five days; though it is not sufficiently sensitive to meet the threshold set by the DoH in the UK, it remains specific.