Humidification of indoor air for preventing or reducing dryness symptoms or upper respiratory infections in educational settings and at the workplace.

BACKGROUND: Indoor exposure to dry air during heating periods has been associated with dryness and irritation symptoms of the upper respiratory airways and the skin. The irritated or damaged mucous membrane poses an important entry port for pathogens causing respiratory infections. OBJECTIVES: To determine the effectiveness of interventions that increase indoor air humidity in order to reduce or prevent dryness symptoms of the eyes, the skin and the upper respiratory tract (URT) or URT infections, at work and in educational settings. SEARCH METHODS: The last search for all databases was done in December 2020. We searched Ovid MEDLINE, Embase, CENTRAL (Cochrane Library), PsycINFO, Web of Science, Scopus and in the field of occupational safety and health: NIOSHTIC-2, HSELINE, CISDOC and the In-house database of the Division of Occupational and Environmental Medicine, University of Zurich. We also contacted experts, screened reference lists of included trials, relevant reviews and consulted the WHO International Clinical Trials Registry Platform (ICTRP). SELECTION CRITERIA: We included controlled studies with a parallel group or cross-over design, quasi-randomised studies, controlled before-and-after and interrupted time-series studies on the effects of indoor air humidification in reducing or preventing dryness symptoms and upper respiratory tract infections as primary outcomes at workplace and in the educational setting. As secondary outcomes we considered perceived air quality, other adverse events, sick leave, task performance, productivity and attendance and costs of the intervention. DATA COLLECTION AND ANALYSIS: Two review authors independently screened titles, abstracts and full texts for eligibility, extracted data and assessed the risks of bias of included studies. We synthesised the evidence for the primary outcomes 'dry eye', 'dry nose', 'dry skin', for the secondary outcome 'absenteeism', as well as for 'perception of stuffiness' as the harm-related measure. We assessed the certainty of evidence using the GRADE system. MAIN RESULTS: We included 13 studies with at least 4551 participants, and extracted the data of 12 studies with at least 4447 participants. Seven studies targeted the occupational setting, with three studies comprising office workers and four hospital staff. Three of them were clustered cross-over studies with 846 participants (one cRCT), one parallel-group controlled trial (2395 participants) and three controlled before-and-after studies with 181 participants. Five studies, all CTs, with at least 1025 participants, addressing the educational setting, were reported between 1963 and 1975, and in 2018. In total, at least 3933 (88%) participants were included in the data analyses. Due to the lack of information, the results of the risk of bias assessment remained mainly unclear and the assessable risks of bias of included studies were considered as predominantly high. Primary outcomes in occupational setting:  We found that indoor air humidification at the workplace may have little to no effect on dryness symptoms of the eye and nose (URT). The only cRCT showed a significant decrease in dry eye symptoms among working adults (odds ratio (OR) 0.54, 95% confidence interval (CI) 0.37 to 0.79) with a low certainty of the evidence. The only cluster non-randomised cross-over study showed a non-significant positive effect of humidification on dryness nose symptoms (OR 0.87, 95% CI 0.53 to 1.42) with a low certainty of evidence. We found that indoor air humidification at the workplace may have little and non-significant effect on dryness skin symptoms. The pooled results of two cluster non-RCTs showed a non-significant alleviation of skin dryness following indoor air humidification (OR 0.66, 95% CI 0.33 to 1.32) with a low certainty of evidence. Similarly, the pooled results of two before-after studies yielded no statistically significant result (OR 0.69, 95% CI 0.33 to 1.47) with very low certainty of evidence No studies reported on the outcome of upper respiratory tract infections. No studies conducted in educational settings investigated our primary outcomes. Secondary outcomes in occupational setting: Perceived stuffiness of the air was increased during the humidification in the two cross-over studies (OR 2.18, 95% CI 1.47 to 3.23); (OR 1.70, 95% CI 1.10 to 2.61) with low certainty of evidence. Secondary outcomes in educational setting: Based on different measures and settings of absenteeism, four of the six controlled studies found a reduction in absenteeism following indoor air humidification (OR 0.54, 95% CI 0.45 to 0.65; OR 0.38, 95% CI 0.15 to 0.96; proportion 4.63% versus 5.08%). AUTHORS' CONCLUSIONS: Indoor air humidification at the workplace may have little to no effect on dryness symptoms of the eyes, the skin and the URT. Studies investigating illness-related absenteeism from work or school could only be summarised narratively, due to different outcome measures assessed. The evidence suggests that increasing humidification may reduce the absenteeism, but the evidence is very uncertain. Future RCTs involving larger sample sizes, assessing dryness symptoms more technically or rigorously defining absenteeism and controlling for potential confounders are therefore needed to determine whether increasing indoor air humidity can reduce or prevent dryness symptoms of the eyes, the skin, the URT or URT infections at work and in educational settings over time.

Human-biomonitoring and individual soil measurements for children and mothers in an area with recently detected mercury-contaminations and public health concerns: a cross-sectional study.

In this study, we assessed intracorporal mercury concentrations in subjects living on partially mercury-contaminated soils in a defined area in Switzerland. We assessed 64 mothers and 107 children who resided in a defined area for at least 3 months. Mercury in biological samples (urine and hair) was measured, a detailed questionnaire was administered for each individual, and individual mercury soil values were obtained. Human biomonitoring results were compared with health-related and reference values. Mothers and children in our study had geometric means (GMs) of 0.22 µg Hg/g creatinine in urine (95th percentile (P95) = 0.85 µg Hg/g) and 0.16 µg Hg/g (P95 = 0.56 µg Hg/g), respectively. In hair, mothers and children had GMs of 0.21 µg Hg/g (P95 = 0.94 µg/g) and 0.18 µg/g (P95 = 0.60 µg/g), respectively. We found no evidence for an association between mercury values in soil and those in human specimens nor for a health threat in residential mothers and children.

Predicted Mercury Soil Concentrations from a Kriging Approach for Improved Human Health Risk Assessment.

Health-risks from contaminated soils are assessed all over the world. An aspect that many risk assessments share is the heterogeneity in the distribution of contaminants. In a preceding study, we assessed potential health-risks for mothers and children living on mercury-contaminated soils in Switzerland using human biomonitoring-values (HBM) and soil samples. We assessed 64 mothers and 107 children who had resided in a defined area for at least 3 months. HBM-concentrations for mercury in urine and hair were measured, a detailed questionnaire was administered for each individual, and more than 4000 individual mercury soil values were obtained in 2015. In this study, we aimed at investigating possible associations of mercury soil- and HBM-values by re-analyzing our data, using predictions of the mercury concentrations at the exact location of the participant’s homes with a kriging approach. Although kriging proved to be a useful method to predict mercury soil concentrations, we did not detect an association between mercury soil- and HBM-values, in agreement with earlier findings. Benefits of geostatistical methods seem to be limited in the context of our study. Conclusions made in our preceding study about potential health risks for the residential population are robust and not altered by the current study.