Image analysis method for evaluation of specific and non-specific hand contamination

To evaluate a quantifying image analysis method for assessing the degree of hand contamination and efficacy of hand washing procedures.

Two types of experimental design were used. In one, different concentrations of pure cultures of Escherichia coli, Listeria innocua and Pseudomonas flourescens were applied to hands. In the other, hands were contaminated by handling various raw foods. Imprints of the contaminated palms were made on 24.5 x 24.5 cm agar plates using appropriate agars. After incubation, digital photographs of the plates were analysed using image analysis. In pure culture studies with selective agars, levels from 1 to 10(6) CFU cm(-2) palm could be monitored. For aerobic, mesophilic organisms from raw chicken, levels from 10(3) to 10(6) CFU cm(-2) palm were correlated linearly to image analysis data.

The image analysis of palm imprints made on agar plates was suitable for assessing the degree of contamination from foods on the palms. Sensitivity and specificity depended on the agar used and the type of contamination encountered.

Data capture by the image analysis method is simple and can be partly automated. Sampling time is short for the person to be tested, which makes it an attractive method for assessing hand hygiene status in larger field trials.