HAND DRYING: A STUDY OF BACTERIAL TYPES ASSOCIATED WITH

DIFFERENT HAND DRYING METHODS AND WITH HOT AIR DRYERS

Keith Redway, Brian Knights, Zoltan Bozoky, Abigail Theobald & Sarah Hardcastle

Applied Ecology Research Group, School of Biosciences,

University of Westminster, 115 New Cavendish Street,

London W1M 8JS UK

January 1994 (20 pages)

SUMMARY

In a previous study (Knights et al., 1993) under naturalistic conditions, towels were found to be more efficient in drying the hands than hot air dryers, many people completing drying on clothes, etc. Microbiological studies revealed that using towels after washing reduced bacterial counts on the hands by an average of 42% (paper) and 10% (cotton). With hot air dryers, however, counts increased by more than 500%. Bacteria were blown out of dryers whenever they were running.

The present study was carried out, using standard techniques, to identify and count the bacteria associated with hand washing and drying, using the same naturalistic conditions in toilets as before. Average bacterial counts were again reduced by using towels (by about 38%), the most significant decrease (58%) being in bacteria grown on nutrient agar after using paper towels. Hot air dryers again produced significant increases in all bacteria (by more than 260%). Types typical of skin (including staphylococci and micrococci) increased by an average of 169%. Skin and gut bacterial counts rose by 438%, the largest increases being in enterobacteria and coliforms, including Escherichia coli (395%). Some types and strains of the bacteria found can be pathogenic. The increases in gut bacteria are indicative of faecal contamination of the hands.

In a further study, bacteria were isolated from swabs taken from the air flow, nozzle and air inlet of 35 hot air dryers in nine types of location (including hospitals, eating places, railway stations, public houses, colleges, shops and sports clubs). Bacteria were relatively numerous in the air flows and on the inlets of 100% of dryers sampled and in 97% of the nozzles. Staphylococci and micrococci (probably from skin and hair) were blown out of 97% of the dryers and 63% showed evidence of the potential pathogen Staphylococcus aureus. At least 6 species of gut bacteria (enterobacteria) were isolated from the air flows of 63% of dryers, indicating faecal contamination.

It is concluded that hot air dryers have the potential for depositing pathogenic bacteria onto the hands and body. Bacteria could be inhaled and are distributed into the general environment whenever dryers are running. It is recommended that the use of hot air dryers should be carefully considered on health grounds, especially in sensitive locations such as hospitals, catering establishments and food preparation areas.