Portable ultrasonic humidifier exacerbates indoor bioaerosol risks by raising bacterial concentrations and fueling pathogenic genera

Abstract

Indoor humidity plays a vital role in occupants' thermal comfort and health. 1 Low relative humidity (RH) may bring static electricity, causing electric failures in offices or homes and arouse discomfort and dry skin, resulting in chapping and respiratory irritation. 2 The situation deteriorates in heating spaces during winter when many homes and offices are usually warmed up by heat pumps or radiant heating systems (e.g., radiant floor heating or radiators). To mitigate the air dryness, portable humidifiers have been increasingly adopted during the heating season. Among the humidifiers, ultrasonic humidifiers are among the most popular types for singleroom humidification. Owing to its unique ultrasonic cavitation effect, 3 the humidifier can atomize water into tiny mists at room temperatures and the atmospheric pressure, realizing the efficient and silent humidification at the cost of little power consumption. Such humidifiers are among the best-selling products, ranking top in the consumer report. 4,5

Punicalagin: a monomer with anti-Eimeria tenella effect from fruit peel of Punica granatum L.

“…Here, our data showed similar results. Acinetobacter and Aerococcus were pathogens ( Rasmussen, 2016 ; Yang et al, 2022b ) and were significantly increased by Punicalagin. This phenomenon needs further study.…”

Exposure at the indoor water–air interface: Fill water constituents and the consequent air emissions from ultrasonic humidifiers: A systematic review

“…Tap water microbial contaminants are demonstrated to be present in humidifier fill water and biofilms 41 and modeling demonstrates that human exposure can occur 42 . Studied microbial‐related emissions from ultrasonic humidifiers include bacteria (e.g., Legionella, E. coli, and Mycobacterium ), fungi, and endotoxins 22,23,43–45 . Compared to evaporative humidifiers, ultrasonic humidifiers clearly emit more waterborne microbial constituents 46 .…”

“…For microorganism and endotoxin emissions, the relationships between fill water and emitted airborne microbes are not as strong as that of PM from TDS or minerals/metals. Pseudomonas , pathogenic Brevundimonas , Acinetobacter , and Legionella were enriched after ultrasonic humidification compared to those in the initial room air 22 . A ranking of exposure routes to Legionella present in tap water, ranked ultrasonic humidifiers as the highest exposure route compared to drinking, showering, and flushing toilets 44 .…”

“…In addition to metals, microorganisms can also occur in tap water and/or fill water of the ultrasonic humidifier 20–22 . Microbial growth in the ultrasonic humidifier reservoir is a possible human health concern since it is acknowledged that growth of microorganisms happens when the humidifier is not cleaned between uses.…”

“…[16][17][18][19] In addition to metals, microorganisms can also occur in tap water and/or fill water of the ultrasonic humidifier. [20][21][22] Microbial growth in the ultrasonic humidifier reservoir is a possible human health concern since it is acknowledged that growth of microorganisms happens when the humidifier is not cleaned between uses. Lee et al 23 filled an ultrasonic humidifier with local tap water, operated the humidifier for 15 days, and collected bioaerosols of bacteria and fungi; results showed that the colony forming unit (cfu) in air increased from 6979 cfu/m 3 on the sixth day to 46 431 cfu/m 3 on the ninth day.…”