Evaluation of test methods and the efficacy of hypochlorous acid water atomization against Pseudomonas aeruginosa in hospital rooms

BACKGROUND: Since the COVID-19 pandemic, the use of hypochlorous acid water has been spreading. However, limited studies have assessed its safety and efficacy when atomised in hospital environments. This study evaluated the disinfection performance of atomised hypochlorous acid water against Pseudomonas aeruginosa, a key pathogen in nosocomial infection control. METHODS: Two test methods for P. aeruginosa, which is susceptible to drying, have been developed. In the first method, 10 μL of bacterial suspension was pipetted onto five spots in a Petri dish, allowed to dry, and solidified (bacterial suspension 'pipetting method'). The second method involved diluting the bacterial suspension 100-fold in saline and pouring 8 mL into a Petri dish (bacterial suspension 'pooling method'). RESULTS: In the pipetting method, no reduction in viable bacteria was observed following atomization of 40 ppm hypochlorous acid water, whereas a significant bactericidal effect (p < 0.001) was detected at 300 ppm. Conversely, in the pooling method, a significant reduction in viable bacteria (p < 0.01) was observed at 40 ppm, with bacterial counts falling below the detection limit at 300 ppm, clearly demonstrating a strong bactericidal effect. The effectiveness of the pooling method may be attributed to enhanced penetration of hypochlorous acid particles, which could promote oxidative action. CONCLUSION: These findings confirm the bactericidal efficacy of hypochlorous acid water atomization in hospital wards against P. aeruginosa. Furthermore, as a performance test, these methods were close to real clinical settings in terms of nutritional conditions and the pooling method could properly evaluate desiccation-sensitive bacteria.