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INTRODUCTION: Our aim was to gain insight into the effect of COVID-19 measures on SARS-CoV-2 incidence in secondary schools and the association with classroom CO 2 concentration and airborne contamination. METHODS: Between October 2020-June 2021, 18 schools weekly reported SARS-CoV-2 incidence and completed surveys on school-initiated COVID-19 measures (e.g. improving hygiene or minimizing contacts). CO 2 was measured in occupied classrooms twice, and SARS-CoV-2 air contamination longitudinally using electrostatic dust collectors (EDC) and analyzed using RT-qPCR. National COVID-19 policy measures varied during pre-lockdown, lockdown and post-lockdown periods. During the entire study, schools were recommended to improve ventilation. SARS-CoV-2 incidence rate ratios (IRR) were estimated by Generalized Estimating Equation (GEE) models. RESULTS: During 18 weeks follow-up (range: 10-22) SARS-CoV-2 school-incidence decreased during national lockdown (adjusted IRR: 0.41, 95%CI: 0.21-0.80) and post-lockdown (IRR: 0.60, 0.39-0.93) compared to pre-lockdown. School-initiated COVID-19 measures had no additional effect. Pre-lockdown, IRRs per 10% increase in time CO 2 exceeded 400, 550 and 800 ppm above outdoor level respectively, were 1.08 (1.00-1.16), 1.10 (1.02-1.19), and 1.08 (0.95-1.22). Post-lockdown, CO 2-concentrations were considerably lower and not associated with SARS-CoV-2 incidence. No SARS-CoV-2 RNA was detected in any of the EDC samples. CONCLUSION: During a period with low SARS-CoV-2 population immunity and increased attention to ventilation, with CO 2 levels most of the time below acceptable thresholds, only the national policy during and post-lockdown of reduced class-occupancy, stringent quarantine, and contact testing reduced SARS-CoV-2 incidence in Dutch secondary schools. Widespread SARS-CoV-2 air contamination could not be demonstrated in schools under the prevailing conditions during the study.

Additional file 1: Box S1. Survey baseline characteristics school. Box S2. Survey school-initiated COVID-19 measures. Table S1. National COVID-19 policy during the study period (October 2020 – June 2021) for each lockdown period. Table S2. School-initiated COVID-19 measures and corresponding scores. Box S3. Laboratory analysis of settling dust samples. Table S3. Results of SARS-CoV-2 RT-PCR in settling dust samples in secondary schools.

Objective: In epidemiological and clinical studies, whole blood assay (WBA) has been used as a measure to characterize inter-individual differences in the cytokine response of individuals exposed to inflammatory agents, such as endotoxins. Several short-time repeatability studies have shown stable cytokine levels in individuals over periods of days, weeks or months, but little is known about the long-term stability of cytokine reactivity.Methods: We studied cytokine response levels in LPS-stimulated whole blood in a cohort of 193 farmers and agricultural industry workers at two time points with a five-year interval.Results: IL-10 and IL-1 beta responses measured with a five-year time interval showed a weak positive correlation (r = 0.22 and 0.27, respectively), whereas no correlation was observed for TNF alpha (r = 0.06). Cytokine reactivity measured repeatedly at the same time point showed high correlations (IL-10 r = 0.80, IL-1 beta r = 0.53 and TNF alpha r = 0.74), suggesting that the observed weak correlations over time are reflective of actual variations in cytokine reactivity over time.Conclusions: Repeatability of ex vivo cytokine reactivity showed to be differential for the measured cytokines, being more stable for IL-10 and IL-1 beta than for TNF alpha. However, in general, repeatability of ex vivo cytokine reactivity was weak, reflecting that cytokine reactivity can mostly be explained by (short term) intra-individual (immunological) or time varying environmental factors and less by genetic or other time-invariant factors. Therefore, WBA should be regarded as a viable tool to study relationships with current health status and exposure, and only partially as a predictor for a future response.

The objective of the present longitudinal study was to investigate the effects of occupational endotoxin exposure on respiratory health and atopic sensitization in adults. Health outcomes and personal endotoxin exposure estimates were determined for 234 farmers and agricultural workers both at baseline and 5 years later. A questionnaire was used to assess respiratory symptoms, spirometry tests were performed and total and specific IgE levels were measured in serum. A twofold increase in personal endotoxin exposure was associated with less hay fever (OR 0.68, 95%CI 0.54-0.87) and grass IgE positivity (OR 0.81, 95%CI 0.68-0.97) at both time points ("persistent" versus "never"). Although not statistically significant, a consistent protective pattern was observed for an increased loss of hay fever symptoms (OR 2.19, 95%CI 0.96-4.99) and grass IgE positivity (OR 1.24, 95%CI 0.76-2.02), and for less new-onset of hay fever (OR 0.87, 95%CI 0.65-1.17), grass IgE positivity (OR 0.83, 95%CI 0.61-1.12) and atopic sensitization (OR 0.75, 95%CI 0.55-1.02). Endotoxin exposure was not associated with changes in lung function. We showed that occupational endotoxin exposure is associated with a long-term protective effect on hay fever and grass IgE positivity. Results on longitudinal changes in hay fever, atopy and grass IgE positivity in adulthood were consistent with a protective effect of endotoxin exposure, but results need to be confirmed in larger cohorts. An effect of endotoxin exposure on lung function decline was not found.

BACKGROUND: Bovine allergens can induce allergic airway diseases. High levels of allergens in dust from stables and homes of dairy farmers have been reported, but sparse knowledge about determinants for bovine allergen levels and associations between exposure level and sensitization is available.OBJECTIVE: To investigate levels and determinants of bovine allergen exposure among dairy, pig and mink farmers (bedroom and stable), and among former and never farmers (bedroom), and to assess the prevalence of bovine allergen sensitization in these groups.METHODS: In 2007-2008, 410 settled dust samples were collected in stables and in bedrooms using an electrostatic dust-fall collector over a 14 day period among 54 pig farmers, 27 dairy farmers, 3 mink farmers as well as 71 former and 48 never farmers in Denmark. For farmers sampling was carried out both during summer and winter. Bovine allergen levels (μg/m(2)) were measured using a sandwich ELISA. Determinants for bovine allergen exposure in stables and bedrooms were explored with mixed effect regression analyses. Skin prick test with bovine allergen was performed on 48 pig farmers, 20 dairy farmers, 54 former and 31 never farmers.RESULTS: Bovine allergen levels varied by five orders of magnitude, as expected with substantially higher levels in stables than bedrooms, especially for dairy farmers. Bovine allergen levels in bedrooms were more than one order of magnitude higher for dairy farmers compared to pig farmers. Former and never farmers had low levels of bovine allergens in their bedroom. Bovine allergen levels during summer appeared to be somewhat higher than during winter. Increased bovine allergen levels in the bedroom were associated with being a farmer or living on a farm. Mechanical ventilation in the bedroom decreased bovine allergen level, significant for dairy farmers β=-1.4, pCONCLUSION: This study confirms high bovine allergen levels in dairy farms, but also suggests sensitization to bovine allergens among Danish farmers to be uncommon. Furthermore the importance of a carrier home effect on allergen load is emphasized. Whether the risk for bovine sensitization is related to the allergen level in the stable or the dwelling remains to be determined.

RATIONALE: A low prevalence of asthma and atopy has been shown in farmers and agricultural workers. However, in these workers, a higher prevalence of respiratory symptoms has been reported, in which T helper 1 (Th1) and/or Th17 responses may play a role.AIM: We investigated the effect of exposure to dust extracts (DEs) from different farms on airway inflammation and T-cell polarisation in a mouse model and assessed T-cell polarisation in agricultural workers from the same farms.METHODS: DEs were prepared from settled dust collected at cattle and pig farms and bulb and onion industries. Mice were exposed to phosphate-buffered saline (PBS), DEs, house dust mite (HDM) or HDM+DE via nasal instillation, four times per week during 5 weeks. Hyperresponsiveness, airway inflammation, IgE levels and T-cell polarisation were assessed. Th-cell and T cytotoxic (Tc)-cell subsets were investigated in peripheral blood samples from 33 agricultural workers and 9 non-exposed controls.RESULTS: DEs induced interleukin(IL)-17, IL-1β and IL-6 in mouse lung homogenates. DE-exposed mice had more mixed inflammatory infiltrates in the lungs, and more neutrophils compared with PBS-exposed mice. DEs protected against the HDM-induced Th2 response and methacholine hyperresponsiveness. Interestingly, occupationally exposed humans had higher frequencies of Th cells spontaneously expressing IL-17 and interferon γ compared with controls.CONCLUSION: Chronic exposure to different types of farm dust induces a Th/Tc-17 inflammatory response in mice and agricultural workers. This may contribute to the low prevalence of Th2-related diseases but may constitute a risk for other chronic respiratory diseases.