Fungal Contamination in Washing Machines with Drying Devices

The extent of fungal contamination in washing machines was compared between those models, increasingly common in recent years, that are fitted with a heat-based drying device, which were sub-divided into drum-type and vertical type models, and those not fitted with such devices (dryerless models). Samples of washing water containing detergent and of rinsing water were collected from 137 washing machines for examination of fungal count and flora. Fungal contamination was found frequently in all types of washing machine; the average mold count in the washing water of drum-type washing machines was 24.0 cfu/ml, or about half that in the dryerless models. However, fungal contamination in washing machines in which the drying device was used once a week or less was significantly higher than in those in which it was used several times a week or daily. Moreover, daily drying operation of as little as 15 minutes seemed to be effective in suppressing fungal contamination. Although Exophiala, Phoma, Scolecobasidium and Phialophora, which use detergent as nutrient, are predominant in all types of washing machine, Acremonium, Alternaria and Penicillium, common in house dust, were found more frequently in washing machines with than in those without drying devices. Fungal contamination in new washing machines was more often detected in those with drying devices than in dryerless washing machines, and, unlike in models of the latter type, average mold count in washing machines with dryers was similar regardless of length of use. Fungal contamination in dryerless models was identified more frequently from the presence of suspended dirt in the washing water than from the smell when the lid was opened, but the reverse applied with drum-type models. The effect of environmental factors on fungal contamination was compared between the two types of washing machine. A number of factors related to moisture, for example the frequency of washing and the floor level, seemed to have a greater effect on dryerless than on drum-type models. Apart from these environmental factors, the form of drying treatment is thought to affect the level of fungal contamination in washing machines with drying devices. The paper also discusses methods of controlling fungal contamination in washing machines with drying devices.