Efficacy of Owner‐Collected Dust Samples in the Evaluation Residential Allergen and Fungal Levels

PS 401‐8 Exposure Assessment of Legionella pneumophila in Nursing Homes of Taiwan C. Chang, N. Chen, Y. Wu, K. Ming, National Taiwan University, Taipei, Taiwan. Objective: An investigation was conducted to assess the exposure risk to Legionella pneumophila in eight nursing homes of Taiwan. Methods: Hot water (HW) and swab samples were taken from the faucets and shower heads. As for cooling tower (CT) samples, cooling water (CW), floating‐biofilm (FB) at the interface between air and water and substrate‐biofilm (SB) from the basin were collected. There were totally 176 samples analyzed by quantitative PCR and culture assays to quantify total and culturable L. pneumophila, respectively. The physical and chemical parameters and the concentrations of heterotrophic plate counts (HPC), Acanthamoeba and Hartmannella vermiformis (two natural hosts for L. pneumophila) in CW and HW were also determined. Results: The highest positive rate for total L. pneumophila was found in CW (74%), followed by SB (53%), FB (48%), HW (32%) and swab (27%), with the mean respective concentrations at 5.29 log cells/L, 5.56 log cells/g, 2.93 log cells/cm2, 4.15 log cells/L and 3.08 cells/cm2. Culturable L. pneumophila was detected in 7‐23% of CT samples, and the respective concentrations were 5.2 log cfu/L, 0.8 log cfu/cm2, 4.7 log cfu/g and 2.4 log cfu/L for CW, FB, SB, and HW. Comparable pH (7.8 vs 7.4) and residual free chlorine (0.8 vs 0.2 mg/L) were found between CW and HW. However, the levels of HPC, Acanthamoeba, H. vermiformis, dissolved organic carbon, total suspended solids and conductivity were all greater in CW than in HW, indicating that CT provided more nutrients and natural hosts than HW, in favor of Legionella colonization and proliferation. This accords with our finding that a greater L. pneumophila contamination in CW. Conclusions: High positive rates and abundances of L. pneumophila were revealed in nursing homes, which concentrations exceeded the action level (1 cell/100 mL) suggested by the WHO for Legionella. Cleaning and disinfection should be performed