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What Risks Does the Residential Laundry Process Pose?: A Quantitative Microbial Risk Assessment (QMRA) Study

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      Background

      Fomites are an important pathway for infectious disease spread in residential and home healthcare settings (i.e., nursing, assisted living, and retirement communities). Many healthcare professionals launder work clothes at home that may be contaminated by contact with infected patients. Through quantitative microbial risk assessment (QMRA), the study objectives were to (1) evaluate pathogen transmission risks for those doing laundry, and (2) compare infection control interventions to reduce laundering risks.

      Methods

      A simulation model was used to evaluate exposure events related to laundry process. One baseline scenario (no handwashing) and three handwashing scenarios (scenario 1: after moving dirty clothes to washing machine, scenario 2: after moving wet clothes to dryer, scenario 3: after both of these previous steps) were evaluated. Each scenario involved a single user, three contacts with contaminated laundry, and three contacts with the face. Five representative microorganisms known to spread via intra-familial transmission were modeled: SARS-CoV-2, rotavirus, norovirus, nontyphoidal Salmonella, and Escherichia coli.

      Results

      The mean infection risks for the baseline scenario were all above a 1 in 1,000,000 risk threshold: 7.22 × 10^(-4) (SARS-CoV-2), 8.74 × 10^(-1) (rotavirus), 7.49 × 10^(-4) (norovirus), 7.12 × 10^(-1) Salmonella), and 1.41 × 10^(-3) (E. coli). Regardless of organism type, handwashing after loading dirty clothes into the washing machine yielded a greater risk reduction (scenario 1: 39.95 – 99.86 %) than handwashing after loading washed clothes into the drying machine (scenario 2: 1.35 – 55.25 %). Handwashing two times (scenario 3) further reduced risk where SARS-CoV-2 achieved 1/1,000,000 risk threshold and norovirus and E. coli achieved 1/10,000 risk threshold.

      Conclusions

      More data is needed to more accurately evaluate real-world exposure potentials (i.e., the hand-to-face contact frequency during laundering and viability of organisms on laundry), however, handling contaminated garments may pose considerable infection risks for some pathogens. To prevent infection, it is important to reduce hand-to-face contacts and to handwash directly after touching contaminated clothing.
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