Ultrasonic humidifiers are commonly used in households to maintain indoor humidity and generate a large number of droplets or spray aerosols. However, there have been various health concerns associated with humidifier use, largely due to aerosols generated during operation. Here, we investigated the size distribution, chemical composition, and charged fraction of aerosol particles emitted from commercial ultrasonic humidifiers. Heavy metals in water used for humidifiers were found to be highly enriched in the ultrasonic humidifier aerosols (UHA), with the enrichment factors ranging from 102 to 107. This enrichment may pose health concerns for the building occupants, as UHA concentrations of up to 106 particles/cm3 or 3 mg/m3 were observed. Furthermore, approximately 90% of UHA were observed to be electrically charged, for the first time according to our knowledge. Based on this discovery, we proposed and tested a new method to remove UHA by using a simple electrical field. The designed electrical field in this work can efficiently remove 81.4% of UHA. Therefore, applying this electrical field could be an effective method to significantly reduce the health risks by UHA.

Next-generation risk assessment (NGRA) has emerged as a promising alternative to non-animal studies owing to the increasing demand for the risk assessment of inhaled toxicants. In this study, NGRA was used to assess the inhalation risks of two biocides commonly used as humidifier disinfectants: polyhexamethylene guanidine phosphate (PHMG-p) and chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT). Human bronchial epithelial cell transcriptomic data were processed based on adverse outcome pathways and used to establish transcriptome-based points of departure (tPODs) for each biocide. tPOD values were 0.00500-0.0510 μg/cm2 and 0.0342-0.0544 μg/cm2 for PHMG-p and CMIT/MIT, respectively. tPODs may provide predictive power comparable to that of traditional animal-based PODs (aPODs). The tPOD-based NGRA determined that both PHMG-p and CMIT/MIT present a high inhalation risk. Moreover, the identified PHMG-p posed a higher risk than CMIT/MIT, and children were identified as more susceptible population compared to adults. This finding is consistent with observations from actual exposure events. Our findings suggest that NGRA with transcriptomics offers a reliable approach for risk assessment of specific humidifier disinfectant biocides, while acknowledging the limitations of current models and in vitro systems, particularly regarding uncertainties in pharmacokinetics (PK) and pharmacodynamics (PD).

BACKGROUND: Lessons learned from the Household Humidifier Disinfectant Tragedy (HHDT) in Korea, which poisoned thousands of citizens over a period of years, necessitated an examination of national poison prevention and surveillance systems. The objectives of this study are to identify essential changes needed in chemical poisoning prevention regulations and surveillance systems for effective poison control by comparing recent trends in international poison control center (PCC) operations, and to delineate the critical elements for establishing a state-of-the-art poison control surveillance system in Korea based on recent advances in PCCs with toxicovigilance.
METHODS: A comprehensive review of Korea\'s regulatory and surveillance systems for chemical health hazards, with a focus on household products under the HHDT, was conducted. A review of toxicovigilance systems in major countries shows that creating an effective national PCC requires key elements: a centralized database of toxic substances and poisoning cases, mandatory or voluntary reporting of poisoning cases, real-time alerts, collaboration among health organizations, and targeted follow-up of poisoned individuals.
RESULTS: Significant deficiencies in Korea\'s legislation, toxicological data management, and poisoning surveillance systems, explained the inadequate response of the Korean government to the HHDT for nearly 17 years until the end of 2011. Based on a review of PCC toxicovigilance systems in major countries, a national framework with five core components is recommended for establishing a modern comprehensive Korea PCC system with toxicovigilance capacity. The core components include establishment of a centralized database of toxic substances information and clinical poisoning cases, implementation of mandatory or permissive reporting of poisoning cases, real-time alert mechanisms, collaborative systems among health-related organizations, and clinical follow-up of poisoned sub-groups.
CONCLUSIONS: A rationale and framework for a state-of-the-art national Korean PCC with toxicovigilance is justified and offered. This proposed system could assist neighboring countries in establishing their own sophisticated, globally integrated PCC networks.

The humidification process of medical gases plays a crucial role in both invasive and non-invasive ventilation, aiming to mitigate the complications arising from bronchial dryness. While passive humidification systems (HME) and active humidification systems are prevalent in routine clinical practice, there is a pressing need for further evaluation of their significance. Additionally, there is often an incomplete understanding of the operational mechanisms of these devices. The current review explores the historical evolution of gas conditioning in clinical practice, from early prototypes to contemporary active and passive humidification systems. It also discusses the physiological principles underlying humidity regulation and provides practical guidance for optimizing humidification parameters in both invasive and non-invasive ventilation modalities. The aim of this review is to elucidate the intricate interplay between temperature, humidity, and patient comfort, emphasizing the importance of individualized approaches to gas conditioning.

A number of biocidal disinfectant chemicals are used as household products to prevent spread of pathogens. People are commonly exposed to multiple chemicals through those disinfectants. However, effects of interactions (e.g., synergism) between disinfectants on human health outcomes have been rarely studied. In this study, we aimed to investigate associations of a mixture of chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) and polyhexamethylene guanidine (PHMG), which had been used as humidifier disinfectants (HDs) in South Korea, with HD-associated lung injury (HDLI) in a Korean population (n = 4058) with HD exposure through use of HD products. Exposure to HD was retrospectively assessed by an interview-based standardized survey, and HDLI was determined by clinical assessment. After adjusting for covariates, PHMG-specific exposure indices (e.g., amount of use, indoor air concentration, and weekly exposure level) were dose-dependently associated with HDLI (their odds ratios for the comparison of third tertile versus first tertile were 1.95, 1.77, and 2.16, respectively). CMIT/MIT exposure was not observed to have a significant association with HDLI in a single chemical exposure model; however, associations between PHMG exposure and HDLI were strengthened by co-exposure to CMIT/MIT in combined chemical exposure models, where synergistic interactions between CMIT/MIT use and PHMG indices (amount of use and weekly exposure level) were observed (p-interaction in additive scale: 0.02 and 0.03, respectively). Our findings imply that adverse effects of PHMG exposure on lung injury among HD users might be worsened by co-exposure to CMIT/MIT. Given that plenty of household products contain disinfectants on global markets, epidemiological and toxicological investigations are warranted on interaction effects of co-exposure to disinfectants.

Introduction: During mechanical ventilation (MV), inspired gases require heat and humidification. However, such conditions may be associated with reduced aerosol delivery efficiency. The practice of turning off heated humidification before nebulization and the impact of nebulization on humidity in a dry ventilator circuit remain topics of debate. This study aimed to assess the effect of turning off heated humidification on inhaled dose and humidity with nebulizer use during adult MV. Methods: A bronchodilator (albuterol) and two antibiotics (Colistimethate sodium and Amikacin sulfate) were nebulized with a vibrating mesh nebulizer placed at the humidifier inlet and in the inspiratory limb at the Y-piece. Additionally, albuterol was nebulized using a jet nebulizer in both placements. Aerosol particle size distribution was determined through a cascade impactor. Absolute humidity (AH) and temperature of inspired gases were determined with anemometer/hygrometers before, during, and after nebulization, before, during, and up to 60 minutes after interrupting active humidification. Aerosol collected on a filter distal to the endotracheal tube and on impactor stages were eluted and assayed by spectrophotometry. Results: The inhaled dose was greater when both nebulizers were placed at the humidifier inlet than the inspiratory limb at the Y-piece. Irrespective of the nebulizer types and placements, the inhaled dose either decreased or showed no significant change after the humidifier was turned off. The aerosol particle size ranged from 1.1 to 2.7 μm. With interruption of active humidification, humidity of inspired gas quickly dropped below recommended levels, and nebulization in dry ventilator circuit produced an AH between 10 and 20 mgH2O/L, lower than the recommended minimum of 30 mgH2O/L. Conclusion: Interrupting active humidification during MV before nebulization did not improve aerosol delivery efficiency for bronchodilator or antibiotics, but did reduce humidity below recommended levels.

RESULTS: After excluding 4 patients with an anesthesia duration of < 2 hours, data from 34 patients (1163 sets of tracheal and esophageal temperatures) were analyzed. Concordance correlation coefficient was 0.78. The overall mean bias (95% limits of agreement) between the tracheal and esophageal temperatures was -0.16°C (-0.65°C to 0.34°C). The percentage of temperature differences within ± 0.25°C was 73.5% ± 32.3, with a median of 89.4% [0,100]. The linear mixed-effects model revealed that the estimated intercept was 0.17°C with a 95% confidence interval (CI) of 0.13°C to 0.22°C. The duration of anesthesia and the number of temperature measurements were associated with higher concordance between the tracheal and esophageal temperatures in univariate analysis.

A humidifier disinfectant (HD) has been prohibited by the government due to its serious effects on the human body. Several studies on the relationship between HD and lung diseases have been performed independently on children and adults. However, there have been no reports on the effects of HD exposure on pregnant women and their foetuses. Therefore, the present study was conducted to investigate the effects of HD exposure on the foetuses of women who encountered HD during pregnancy. A total of 56 cases were recruited from 2017 to 2019 through the Korea Environmental Industry & Technology Institute, and data obtained from the medical records included maternal date of birth, maternal date of death, maternal start and end date of HD exposure, maternal date of symptom onset, neonatal birthday, neonatal birthweight, gestational age, and neonatal survival status within 28 days. All data were retrospectively investigated through medical records. Of the 47 mothers, 20 (42.6%) mothers survived, and 27 (57.4%) mothers died. In the group of survivors, there was a shorter period of total HD use, period of HD use before pregnancy and period of HD use to onset of symptoms. Shorter durations of HD use resulted in higher survival rate of mothers. HD use caused an increase in gestational age surviving foetuses, and foetal mortality increased when clinical symptoms developed before birth.

OBJECTIVE: Inhalation exposure to humidifier disinfectants has resulted to various types of health damages in Korea. To determine the epidemiological correlation necessary for presuming the legal causation, we aimed to develop a method to synthesize the entire evidence.
METHODS: Epidemiological and toxicological studies are systematically reviewed. Target health problems are selected by criteria such as frequent complaints of claimants. Relevant epidemiologic studies are reviewed and the risk of bias and confidence level of the total evidence are evaluated. Toxicological literature reviews are conducted on three lines of evidence including hazard information, animal studies, and mechanistic studies, considering the source-to-exposure-to-outcome continuum. The confidence level of the body of evidence is then translated into the toxicological evidence levels for the causality between humidifier disinfectant exposure and health effects. Finally, the levels of epidemiological and toxicological evidence are synthesized.
RESULTS: Under the Special Act revised in 2020, if the history of exposure and the disease occurred/worsened after exposure were approved, and the epidemiological correlation between the exposure and disease was verified, the legal causation is presumed unless the company proves the evidence against it. The epidemiological correlation can be verified through epidemiological investigations, health monitoring, cohort investigations and/or toxicological studies. It is not simply as statistical association as understood in judicial precedents, but a general causation established by the evidence as a whole, i.e., through weight-of-the-evidence approach.
CONCLUSIONS: The weight-of-the-evidence approach differs from the conclusive single study approach and this systematic evidence integration can be used in presumption of causation.

OBJECTIVE: The humidifier disinfectant catastrophe in South Korea was a social disaster caused by toxic chemical substances. The present study aimed to examine the relationships between psychological symptoms and adaptive life functioning in survivors of humidifier disinfectants. This study examined the differential effects of psychological symptoms on life adjustment between survivors of humidifier disinfectant and the general population.
METHODS: A total of 452 individuals (228 general and 224 survivor groups) participated in this research. This study utilized the Adult Self-Report, one of the most widely used comprehensive mental health scales for measuring both psychological symptoms (e.g., anxiety/depression) and life adjustment functioning (e.g., interpersonal relationship). For the data analysis, multi-group structural equation modeling analysis was conducted using AMOS 21.0 program.
RESULTS: The results of this study indicated that attention problems out of 8 psychological symptoms was the only significant factor related to life adjustment in both general and survivor groups. In addition, there was a significant 2-way interaction effect of group status and somatic complaints on life adjustment.
CONCLUSIONS: When the somatic complaint symptom was higher, participants in the survivor group were less likely to adjust in life than the general group. Taken together, the somatic complaints of the survivors more strongly influence the life adjustment than the general population. Finally, the authors discuss practical implications for survivors of humidifier disinfectants for designing suitable intervention strategies.Int J Occup Med Environ Health. 2023;36(5):596-605.