Evaluation of the occurrence and risk of microbes in laundry and laundry-associated surfaces

Viable bacteria have been found on environmental surfaces, including washed and unwashed clothing, and places that come into contact with laundry. Under certain conditions, clothing contaminated with pathogenic organisms may present a health risk to the laundry handler. This research project focused on (i) evaluating Staphylococcus aureus and MRSA survival using front-load and top-load washing machines; (ii) determining relative microbial levels on new, disposable, laundered and unlaundered hospital scrubs; (iii) characterizing the relative hygiene of public and apartment laundromat surfaces; and (iv) developing a quantitative risk assessment for laundry handlers.;Standard microbial evaluation techniques were used to identify and quantify a variety of microorganisms on fabrics and environmental surfaces, including HPC bacteria, S. aureus, MRSA, total coliforms and Escherichia coli. S. aureus and MRSA were exclusively used during evaluation of bacteria reduction levels achieved by front- and top-load washers. Results from this research indicate: (i) Washing in either a top- or front-load washer affords a 5--6 log10 reduction of S. aureus and MRSA when detergent is used. If complete drying and/or bleach are also employed, a 6--7 log10 reduction is achieved and few organisms remain. (ii) Bacteria cross-contamination of other fabrics within a laundry load is common for both types of washers and between loads on the interior of top-load washers. (iii) Significantly fewer bacteria (p=0.044) were detected on hospital-laundered scrubs than on home-laundered scrubs. (iv) Laundromat surfaces can be contaminated with substantial numbers of bacteria and the potential exists for transfer of bacteria from a past user to the next laundromat patron. (v) The risk of acquiring a S. aureus infection after handling unwashed laundry contaminated with an initial S. aureus level of 106 CFU/cm 2 was estimated to be 0.59 infections per person per year. The estimated risk became negligible if handling washed laundry.