Is it really clean? Evaluation of the DAZO Fluorescent Marker Method for Monitoring Environmental Cleaning

Background: The DAZO^TM fluorescent targeting method has been developed as a means to objectively evaluate the thoroughness of cleaning of high-touch surfaces in healthcare settings. However, few studies have validated the effectiveness of this method as a means to monitor room disinfection.

Objective: To test the hypothesis that removal of DAZO from selected sites on high-touch surfaces correlates with removal of bacteria from those sites and with cleaning of alternate sites on the same surfaces.

Methods:  In 50 rooms being cleaned by housekeepers, DAZO was applied to high-touch surfaces (i.e., bed rail, top surface; bedrail, bottom surface; bedside table, top surface; bedside table, bottom hand grip; call button; telephone; toilet seat; and bathroom hand rail) before cleaning and removal (graded as complete, partial, or no removal) was assessed after cleaning. Non-toxigenic C. difficile spores (~4 log₁₀colony-forming units) were inoculated onto a 1 cm² area of 4 sites (table, bed rail, call button, telephone) directly adjacent to the DAZO placement and quantitative cultures were performed after cleaning. For the same 4 sites, cultures for total aerobic bacteria were collected before and after cleaning. 

Results: Only 46% of sites had complete removal of DAZO and there was wide variation among sites (Figure). Removal of DAZO correlated inversely with total bacterial counts (correlation coefficient -0.50; P<0.01) and positively with removal of C. difficile spores (correlation coefficient -0.63; P<0.01). DAZO was completely removed from 66%-76% of the top surfaces of the bed rail and bedside table, but from <20% of the bottom surfaces.

Conclusions: Removal of DAZO correlated well with removal of bacteria or C. difficile spores from the site of marker placement, but did not ensure that other high-touch sites on the same surfaces were cleaned.