Indoor humidity levels and associations with reported symptoms in office buildings

Indoor air humidity revisited: Impact on acute symptoms, work productivity, and risk of influenza and COVID-19 infection

Recent epidemiological and experimental findings reconfirm that low indoor air humidity (dry air) increases the prevalence of acute eye and airway symptoms in offices, result in lower mucociliary clearance in the airways, less efficient immune defense, and deteriorate the work productivity. New epidemiological and experimental research also support that the environmental conditions for the risk of infection of influenza and COVID-19 virus is lowest in the Goldilocks zone of 40-60% relative humidity (RH) by decrease of the airways' susceptibility, which can be elevated by particle exposure. Furthermore, low RH increases the generation of infectious virus laden aerosols exhaled from infected people. In general, elevation of the indoor air humidity from dry air increases the health of the airways concomitantly with lower viability of infectious virus. Thus, the negative effects of ventilation with dry outdoor air (low absolute air humidity) should be assessed according to 1) weakened health and functionality of the airways, 2) increased viability and possible increased transmissibility of infectious virus, and 3) evaporation of virus containing droplets to dry out to droplet nuclei (also possible at high room temperature), which increases their floating time in the indoor air. The removal of acid-containing ambient aerosols from the indoor air by filtration increases pH, viability of infectious viruses, and the risk of infection, which synergistically may further increase by particle exposure. Thus, the dilution of indoor air pollutants and virus aerosols by dry outdoor air ventilation should be assessed and compared with the beneficial health effects by control of the center zone of 40-60% RH, an essential factor for optimal functionality of the airways, and with the additional positive impact on acute symptoms, work productivity, and reduced risk of infection.

Growing Safer Greens: Exploring Food Safety Practices and Challenges in Indoor, Soilless Production Through Thematic Analysis of Leafy Greens Grower Interviews

Indoor, soilless production-often referred to more broadly as controlled environment agriculture (CEA)-is increasingly used for the cultivation of leafy greens. Minimal information is currently available regarding food safety practices during production and distribution of leafy greens grown within indoor, soilless environments in the United States (U.S.). This study aimed to describe production challenges and implementation of good agricultural practices among CEA growers. Data collection methods included semi-structured interviews (N = 25) and a supplemental online survey completed by growers (N = 12) in the U.S. Out of 18 total responses (i.e., multiple responses allowed per completed survey), survey data indicated that lettuce (n = 5; 27.8%) was the most commonly grown leafy green, followed by culinary herbs (n = 3; 16.7%) and arugula (n = 3; 16.7%). Most growers (n = 7; 58.3%) grew other agricultural products, specifically other crops in addition to leafy greens. Revenue from sales ranged from US$500 000 per year. Meanwhile, nearly half (n = 5; 45.5%) of respondents (N = 11) were uncertain whether their produce was subject to the FSMA Produce Safety Rule. Most survey respondents used vertical farming techniques (5 out of 11; 45.5%) or some variety of greenhouse (4 out of 11; 36.4%). Based on 35 total responses, leafy greens were most commonly sold to "Commercial Restaurants" (n = 7; 20.0%), "Grocery Stores" (n = 7; 20.0%), "Institutional Foodservice Establishments (hospitals, schools, childcare, long-term care)" (n = 6; 17.1%), and "Wholesaler/Distributers" (n = 6; 17.1%). The 11 interview questions elucidated three major themes: contextual, barriers to risk management and regulatory compliance, and research needs. Thirteen subthemes were identified, and an example of a subtheme within each major theme, respectively, includes worker hygiene and training, regulatory and certification environment, and risk assessments of individual issues.

Carbohydrate vitrification in aerosolized saliva is associated with the humidity-dependent infectious potential of airborne coronavirus

An accepted murine analogue for the environmental behavior of human SARS coronaviruses was aerosolized in microdroplets of its culture media and saliva to observe the decay of its airborne infectious potential under relative humidity (RH) conditions relevant to conditioned indoor air. Contained in a dark, 10 m³ chamber maintained at 22°C, murine hepatitis virus (MHV) was entrained in artificial saliva particles that were aerosolized in size distributions that mimic SARS-CoV-2 virus expelled from infected humans' respiration. As judged by quantitative PCR, more than 95% of the airborne MHV aerosolized was recovered from microdroplets with mean aerodynamic diameters between 0.56 and 5.6 μm. As judged by its half-life, calculated from the median tissue culture infectious dose (TCID₅₀), saliva was protective of airborne murine coronavirus through a RH range recommended for conditioned indoor air (60% < RH < 40%; average half-life = 60 minutes). However, its average half-life doubled to 120 minutes when RH was maintained at 25%. Saliva microaerosol was dominated by carbohydrates, which presented hallmarks of vitrification without efflorescence at low RH. These results suggest that dehydrating carbohydrates can affect the infectious potential coronaviruses exhibit while airborne, significantly extending their persistence under the drier humidity conditions encountered indoors.

A longitudinal study on the effects of hygro-thermal conditions and indoor air pollutants on building-related symptoms in office buildings

We conducted a longitudinal epidemiological study for over 1 year in Tokyo and Osaka, Japan, beginning June 2015, to examine the association between indoor environmental factors and building-related symptoms (BRSs) in office workers. Data were obtained from 483 subjects (225 females and 258 males) in 24 office rooms in 11 office buildings. Environmental monitoring was conducted for hygro-thermal conditions and carbon dioxide and sampling was performed for indoor air pollutants. Questionnaires were concurrently administered to collect information on participants' perceptions of their comfort and health and the conditions of the work environments. Multivariable analyses revealed that upper respiratory symptoms were significantly correlated with a decrease in both relative [odds ratio (OR): 0.77; 95% confidence intervals (CI): 0.62-0.95; p = 0.014] and absolute humidity (OR: 0.89; 95% CI: 0.81-0.97; p = 0.008). Statistically, significant evidence was found that average relative humidity of <38% (OR: 2.68; 95% CI: 1.36-5.27; p = 0.004) showed the most significant association with increased risk of upper respiratory symptoms. Air concentrations of carbon dioxide showed no significant correlation with BRSs at mean concentrations <1000 ppm in most buildings surveyed. Most indoor air pollutant concentrations were relatively low or lower than the values set by indoor air quality guidelines and the values of thresholds for sensory irritation. Air concentrations of indoor air pollutants showed no significant correlation with BRSs. Our data emphasize the importance of appropriate humidity control during low humidity in winter.