Symptom-based assessment during prolonged low-concentration atomization of hypochlorous acid in occupied hospital rooms: A controlled pilot study

Introduction Information on health effects during prolonged low-concentration atomization of hypochlorous acid in occupied hospital rooms is limited. Methods We conducted a single-centre controlled pilot study in occupied four-bed hospital rooms. Rooms were assigned non-randomly to atomization with hypochlorous acid solution (24 enrolled patients) or tap water (16 enrolled patients). Participants and nurses conducting the symptom assessments were blinded to the atomized solution. Atomization was performed for 12 h/day over a 30-day room-level intervention period, with a target airborne available chlorine concentration of 0.02 ppm. Prespecified symptoms were assessed daily using patient self-reports and nurse observations. No objective respiratory, physiological, or toxicological measurements were performed. Results One participant in each group died during the study period; both deaths were assessed by the investigator as unrelated to the assigned atomization intervention. The remaining 23 participants in the hypochlorous acid group and 15 in the tap-water group completed the 30-day observation period and were included in the final analysis. The measured airborne available chlorine concentration ranged from 0.02 to 0.04 ppm, with an average of approximately 0.03 ppm. No prespecified symptoms were reported by participants or observed by nurses in either group. Discussion Under the specific conditions evaluated, no prespecified symptoms were reported or observed. However, the small sample size and absence of objective respiratory, physiological, and toxicological assessments preclude conclusions regarding safety. The study did not evaluate airborne viral concentrations, infection rates, or clinical effectiveness.