Spatiotemporal patterns of PM10 concentrations over China during 2005-2016: A satellite-based estimation using the random forests approach

BACKGROUND

Few studies have estimated historical exposures to PM₁₀ at a national scale in China using satellite-based aerosol optical depth (AOD). Also, long-term trends have not been investigated.

OBJECTIVES

In this study, daily concentrations of PM₁₀ over China during the past 12 years were estimated with the most recent ground monitoring data, AOD, land use information, weather data and a machine learning approach.

METHODS

Daily measurements of PM₁₀ during 2014-2016 were collected from 1479 sites in China. Two types of Moderate Resolution Imaging Spectroradiometer (MODIS) AOD data, land use information, and weather data were downloaded and merged. A random forests model (non-parametric machine learning algorithms) and two traditional regression models were developed and their predictive abilities were compared. The best model was applied to estimate daily concentrations of PM₁₀ across China during 2005-2016 at 0.1⁰ (≈10 km).

RESULTS

Cross-validation showed our random forests model explained 78% of daily variability of PM₁₀ [root mean squared prediction error (RMSE) = 31.5 μg/m³]. When aggregated into monthly and annual averages, the models captured 82% (RMSE = 19.3 μg/m³) and 81% (RMSE = 14.4 μg/m³) of the variability. The random forests model showed much higher predictive ability and lower bias than the other two regression models. Based on the predictions of random forests model, around one-third of China experienced with PM₁₀ pollution exceeding Grade Ⅱ National Ambient Air Quality Standard (>70 μg/m³) in China during the past 12 years. The highest levels of estimated PM₁₀ were present in the Taklamakan Desert of Xinjiang and Beijing-Tianjin metropolitan region, while the lowest were observed in Tibet, Yunnan and Hainan. Overall, the PM₁₀ level in China peaked in 2006 and 2007, and declined since 2008.

CONCLUSIONS

This is the first study to estimate historical PM₁₀ pollution using satellite-based AOD data in China with random forests model. The results can be applied to investigate the long-term health effects of PM₁₀ in China.

Spatiotemporal and demographic variation in the association between temperature variability and hospitalizations in Brazil during 2000-2015: A nationwide time-series study

BACKGROUND

Extreme temperature events are known to be adversely associated with a range of health outcomes, but little is known about the effect of less extreme, but more frequent fluctuation in temperature. We examined the spatiotemporal and demographic variation in the effect of temperature variability (TV) on nationwide hospitalizations in Brazil during 2000-2015.

METHODS

Data on daily hospitalizations and weather variables were collected from 1814 cities, comprising 78.4% of Brazilian population. TV was defined as the standard deviation of daily minimum and maximum temperatures during exposure days. City-specific TV effect was estimated using a quasi-Poisson regression model, and then pooled at the national and regional level using meta-analysis. Stratified analyses were performed by sex, 10 age-groups, and 11 cause categories. Meta-regression was applied to city-year-specific estimates to examine the temporal change.

RESULTS

The estimate of TV effect peaked on 0-1 days' exposure, contributing to 3.5% [95% confidence interval (CI): 3.1-3.8%] of hospitalizations nationwide, equalling 221 (95%CI: 200-242) cases per 100,000 population annually. The effect estimate varied across 11 cause categories, which was strongest for respiratory admissions. Males, particular those 10-49 year old were more affected than females but there was no sex difference for the attributable hospitalization rate. The attributable rate for the under-fives was twice as high as for the elderly, and five times higher than in adults. The majority of the most affected cities were located in the central west and the inland of northeast. The risk of hospitalization related to TV showed a significant increase over the 16-year period at the national level.

CONCLUSIONS

In Brazil, the effect of TV on hospitalization is acute, and varies by spatial, sex, age, and cause category. Given there is no evidence regarding TV adaptation, hospitalization burden associated with TV is likely to further increase and warrants consideration when developing future public health policies in the context of climate change.

Personal Exposure to Radio Frequency Electromagnetic Fields among Australian Adults

The measurement of personal exposure to radiofrequency electromagnetic fields (RF-EMFs) is important for epidemiological studies. RF-EMF exposure can be measured using personal exposimeters that register RF-EMFs over a wide range of frequency bands. This study aimed to measure and describe personal RF-EMF exposure levels from a wide range of frequency bands. Measurements were recorded from 63 participants over an average of 27.4 (±4.5) hours. RF-EMF exposure levels were computed for each frequency band, as well as from downlink (RF from mobile phone base station), uplink (RF from mobile phone handsets), broadcast, and Wi-Fi. Participants had a mean (±SD) age of 36.9 ± 12.5 years; 66.7% were women; and almost all (98.2%) from urban areas. A Wi-Fi router at home was reported by 61 participants (96.8%), with 38 (61.2%) having a Wi-Fi enabled smart TV. Overall, 26 (41.3%) participants had noticed the existence of a mobile phone base station in their neighborhood. On average, participants estimated the distance between the base station and their usual residence to be about 500 m. The median personal RF-EMF exposure was 208 mV/m. Downlink contributed 40.4% of the total RF-EMF exposure, followed by broadcast (22.4%), uplink (17.3%), and Wi-Fi (15.9%). RF-EMF exposure levels on weekdays were higher than weekends (p < 0.05). Downlink and broadcast are the main contributors to total RF-EMF personal exposure. Personal RF-EMF exposure levels vary according to day of the week and time of day.

Is exposure to personal music players a confounder in adolescent mobile phone use and hearing health studies?

Objective

This study was performed to determine whether exposure to personal music players (PMPs) in the immediate morning prior to hearing testing confounds the association between mobile phone use and hearing thresholds of adolescents.

Design

In this cohort study of cognitive function in year 7 students (median age 13 years, range 11–14), information regarding the weekly use of mobile phones and the use of PMPs was assessed by a questionnaire. Pure-tone audiometry was used to establish hearing thresholds for all participants.

Results

Among a cohort of 317 adolescents (60.9% females), 130 were unexposed to PMP use while 33 were exposed to PMP use in the morning prior to hearing testing. No statistically significant difference in hearing threshold shifts was found between adolescents who were and were not exposed to PMP use prior to hearing testing. Likewise, the difference in the use of mobile phones according to the PMP use status was not statistically significant.

Conclusion

Exposure to PMPs prior to hearing testing did not introduce confounding in the present study of mobile phone use and hearing loss among adolescents.

The prevalence of exposure to high molecular weight asthmagens derived from plants among workers in Australia

BACKGROUND

Limited information is available on exposure to high molecular weight (HMW) asthmagens derived from plants and on the main occupations and tasks that result in such exposure among workers.

METHODS

Data were collected as part of the Australian Work Exposures Study-Asthma. We estimated adjusted prevalence ratios (aPR) using modified Poisson regression models to determine which factors were associated with exposure.

RESULTS

A 12.8% of 4878 workers were exposed to HMW asthmagens derived from plants. The highest prevalence of exposure was found among farmers/animal workers, education workers, and food processing workers. The main circumstances of exposure were through handling flour, freesias, or through raising livestock. Exposure was more common among female workers (aPR = 1.26, 1.10-1.43) than males, while it was lower among workers born overseas (aPR = 0.70, 0.57-0.86) than those born in Australia.

CONCLUSION

Prevention of exposure to HMW asthmagens derived from plants requires a broad strategy targeting different tasks and occupations.

Environmental grass pollen levels in utero and at birth and cord blood IgE: Analysis of three birth cohorts

BACKGROUND

Early life factors are associated with allergic respiratory diseases, but the role of high grass pollen concentrations during pregnancy and shortly after birth is not known.

OBJECTIVE

To assess outdoor levels of grass pollen during the intrauterine period and at birth during peak pollen season on cord blood IgE in birth cohorts.

METHODS

Three birth cohorts were included: MACS (n = 429), Australia; COPSAC₂₀₀₀ (n = 200), Denmark; and LISA (n = 1968), Germany. Cord blood IgE was categorized (<0.5 kU/L, 0.5-1 kU/L, >1 kU/L) and dichotomized (high IgE ≥ 0.5 kU/L). Birth during the grass pollen season months and cumulative exposure to outdoor grass pollen counts during pregnancy with cord blood IgE were analysed using multinomial regression and analysed in meta-analysis using binomial regression adjusted for potential confounders.

RESULTS

Birth during the grass pollen season had higher pooled odds of cord blood IgE >0.5 kU/L 1.37 (95% CI 1.06, 1.77) in a meta-analysis with little heterogeneity between the three cohorts. Cumulative exposure to outdoor grass pollen counts during the entire pregnancy was associated with slightly lower pooled odds but significant (OR = 0.98, 95% CI: 0.96 to 0.99).

CONCLUSIONS

Birth during grass pollen seasons were associated with increased risk of high cord blood IgE in cities from both hemispheres, but high pollen loads in the environment during the entire pregnancy appeared protective. As IgE responses develop during the first months of life, our study findings provide new insights into the mechanisms of grass pollen exposure at birth and shortly after on possible allergic respiratory diseases.

A machine learning method to estimate PM2.5 concentrations across China with remote sensing, meteorological and land use information

BACKGROUND

Machine learning algorithms have very high predictive ability. However, no study has used machine learning to estimate historical concentrations of PM_2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) at daily time scale in China at a national level.

OBJECTIVES

To estimate daily concentrations of PM_2.5 across China during 2005-2016.

METHODS

Daily ground-level PM_2.5 data were obtained from 1479 stations across China during 2014-2016. Data on aerosol optical depth (AOD), meteorological conditions and other predictors were downloaded. A random forests model (non-parametric machine learning algorithms) and two traditional regression models were developed to estimate ground-level PM_2.5 concentrations. The best-fit model was then utilized to estimate the daily concentrations of PM_2.5 across China with a resolution of 0.1° (≈10 km) during 2005-2016.

RESULTS

The daily random forests model showed much higher predictive accuracy than the other two traditional regression models, explaining the majority of spatial variability in daily PM_2.5 [10-fold cross-validation (CV) R² = 83%, root mean squared prediction error (RMSE) = 28.1 μg/m³]. At the monthly and annual time-scale, the explained variability of average PM_2.5 increased up to 86% (RMSE = 10.7 μg/m³ and 6.9 μg/m³, respectively).

CONCLUSIONS

Taking advantage of a novel application of modeling framework and the most recent ground-level PM_2.5 observations, the machine learning method showed higher predictive ability than previous studies.

CAPSULE

Random forests approach can be used to estimate historical exposure to PM_2.5 in China with high accuracy.

NOx in exhaled breath condensate is related to allergic sensitization in young and middle-aged adults

BACKGROUND

Asthma and allergic diseases are heterogeneous. Measurement of biomarkers in exhaled breath condensate (EBC) may help to discriminate between different phenotypes and may assist with clinical prognostication.

OBJECTIVES

We aimed to assess associations between total nitric oxide products (NO_x ) in EBC and different allergic phenotypes and lung function in young and middle-aged adults.

METHODS

Cross-sectional analyses were nested within two Australian longitudinal studies, the Melbourne Atopy Cohort Study (MACS, mean age 17.8 years) and the Tasmanian Longitudinal Health Study (TAHS, mean age 49.4 years). Levels of EBC NO_x were determined by Griess-reaction fluorescent method. Associations were assessed between EBC NO_x and different allergic phenotypes, lung function and airway reactivity.

RESULTS

Atopy, with or without asthma or rhinitis, was associated with increased EBC NO_x levels particularly in individuals with poly-aero-sensitization. These findings were generally consistent across the two age groups. In the older cohort, use of ICS in the previous 12 months masked the association between sensitization and EBC NO_x (OR = 0.64, 95% CI = 0.21-1.96, p for interaction = 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

In these population-based samples, EBC NO_x was most strongly associated with atopic sensitization, rather than either current asthma or rhinitis, possibly indicating underlying increased airway inflammation associated with atopy. Therefore, EBC NO_x could be a key predictor of atopy in both young and middle-aged adults, regardless of the presence of concomitant asthma or rhinitis.

Latex glove use among healthcare workers in Australia

BACKGROUND

Exposure to natural rubber latex, primarily through the use of gloves, is a well-recognized cause of occupational asthma. We investigated latex glove use among Australian workers and estimated the resultant burden of occupational asthma among healthcare workers (HCWs).

METHODS

Data were collected in 2014 as part of the Australian Work Exposures Study-Asthma, a telephone survey investigating the prevalence of current occupational exposure to asthmagens, including latex. We estimated adjusted prevalence ratios (aPRs) to determine variables associated with the use of latex gloves among HCWs and calculated the asthma-related disability-adjusted life years due to latex exposure among HCWs.

RESULTS

Latex gloves were used by 22% of respondents. Almost two-thirds (63%) of HCWs reported wearing latex gloves, with 26% using powdered latex gloves. The use of latex gloves was more common among those employed in micro companies (less than 5 employees) than large companies (200+ employees) (aPR = 1.5, 95% confidence interval 1.1-2.0). Latex exposure in HCWs was estimated to contribute 3% of the total asthma-related burden.

DISCUSSION

Latex gloves are widely used by Australian workers and by HCWs in particular.

CONCLUSIONS

This is the first estimate of the burden of asthma attributable to occupational exposure to latex among HCWs. These results can be used to guide decisions regarding the control of occupational exposure to latex.

High ambient levels of grass, weed and other pollen are associated with asthma admissions in children and adolescents: A large 5-year case-crossover study

BACKGROUND

Pollen is an important aeroallergen that triggers asthma exacerbations in children, but we know little about the impact of different pollen types in cities with varying climatic conditions and pollen seasons.

OBJECTIVES

We aimed to assess the role of ambient level of different types of pollen on a large time series of child and adolescent asthma hospitalizations in Sydney, Australia.

METHODS

Childhood asthma hospitalization and the daily ambient pollen concentrations of different species were collected in South-West Sydney. With a bidirectional case-crossover design, we fitted conditional logistic regression models to measure the associations between instantaneous and up to 3 days lagged effects of pollen concentrations on asthma hospitalizations after controlling for potential confounders and testing for interactions.

RESULTS

A total of 2098 children, more boys (59.7%) and 2-5 years old (62.6%), were hospitalized due to asthma. The geometric mean concentration of Cupressus, 7.88 [5.02] grains/m³ , was the highest during the study period. The increase from 75th to 90th percentile of grass (OR = 1.037, 95% CI 1.005-1.070), weed other than Plantago species (OR = 1.053, 95% CI 1.009-1.098) and unclassified pollen (OR = 1.034, 95% CI 1.010-1.058) were significantly associated with the odds of asthma hospitalizations. Boys were at greater risk of asthma exacerbations associated with grass (OR = 1.046, 95% CI 1.003-1.090) and unclassified pollen (OR = 1.041, 95% CI 1.010-1.073). There was evidence of effect modification by age groups for Cupressus, conifer, total tree and total pollen.

CONCLUSIONS

Although boys are more vulnerable to grass pollen, weed, and other pollen are also important triggers of asthma exacerbations in all children and adolescents. These findings are important for urban green space planning and the development of pollen monitoring systems for families with children at risk of asthma exacerbations during peak pollen seasons.

Airway smooth muscle proliferation and inflammation in asthma

In asthma, it is unclear if the airway smooth muscle cells proliferate more or are increased at the onset of asthma and remain stable. This study aimed to compare smooth muscle cell proliferation in individuals with and without asthma and correlate proliferation rates with cell size and number and with granulocytic airway inflammation. Postmortem airway sections were labeled with proliferating cell nuclear antigen (PCNA) and percent positive muscle cells calculated. On the same sections, smooth muscle cell size and number and the number of eosinophils and neutrophils were estimated and compared in cases of nonfatal ( n = 15) and fatal ( n = 15) asthma and control subjects ( n = 15). The %PCNA⁺ muscle cells was not significantly different in fatal (29.4 ± 7.7%, mean ± SD), nonfatal asthma (28.6 ± 8.3%), or control subjects (24.6 ± 6.7%) and not related to mean muscle cell size ( r = 0.09), number ( r = 0.36), thickness of the muscle layer ( r = 0.05), or eosinophil numbers ( r = 0.04) in the asthma cases. These data support the hypothesis that in asthma the increased thickness of the smooth muscle layer may be present before or at the onset of asthma and independent of concurrent granulocytic inflammation or exacerbation. NEW & NOTEWORTHY There is debate regarding the origins of the increased airway smooth muscle in asthma. It may be independent of inflammation or arise as a proliferative response to inflammation. The present study found no increase in the proportion of proliferating smooth muscle cells in asthma and no relation of proliferation to numbers of airway smooth muscle cells or inflammation. These results support a stable increase in smooth muscle in asthma that is independent of airway inflammation.

Diagnosis of concomitant inducible laryngeal obstruction and asthma

BACKGROUND

Inducible laryngeal obstruction, an induced, inappropriate narrowing of the larynx, leading to symptomatic upper airway obstruction, can coexist with asthma. Accurate classification has been challenging because of overlapping symptoms and the absence of sensitive diagnostic criteria for either condition.

OBJECTIVE

To evaluate patients with concomitant clinical suspicion for inducible laryngeal obstruction and asthma. We used a multidisciplinary protocol incorporating objective diagnostic criteria to determine whether asthma, inducible laryngeal obstruction, both, or neither diagnosis was present.

METHODS

Consecutive patients were prospectively assessed by a laryngologist, speech pathologist and respiratory physician. Inducible laryngeal obstruction was diagnosed by visualizing paradoxical vocal fold motion either at baseline or following mannitol provocation. Asthma was diagnosed by physician assessment with objective variable airflow obstruction. Validated questionnaires for laryngeal dysfunction and relevant comorbidities were administered.

RESULTS

Of 69 patients, 15 had asthma alone, 11 had inducible laryngeal obstruction alone and 14 had neither objectively demonstrated. Twenty-nine patients had both diagnoses. In 19 patients, inducible laryngeal obstruction was only seen following provocation. Among patients with inducible laryngeal obstruction, chest tightness was more frequent with concurrent asthma. Among patients with asthma, stridor was more frequent with concurrent inducible laryngeal obstruction. Cough was more frequently found in asthma alone, whereas difficulty with inspiration and symptoms triggered by psychological stress were more frequently found in inducible laryngeal obstruction alone. Patients with asthma alone had greater airflow obstruction. Relevant comorbidities were frequent (rhinitis in 85%, gastro-oesophageal reflux in 65%), and questionnaire scores for laryngeal dysfunction were abnormal. However, neither comorbidities nor questionnaires differentiated patients with or without inducible laryngeal obstruction.

CONCLUSIONS AND CLINICAL RELEVANCE

In this cohort with suspected inducible laryngeal obstruction and asthma, 42% had objective evidence of both conditions. Clinical assessment, questionnaire scores and comorbidity burden were not sufficiently discriminatory for diagnosis, highlighting the necessity of objective diagnostic testing.

Prediction models for the development of COPD: a systematic review

Early identification of people at risk of developing COPD is crucial for implementing preventive strategies. We aimed to systematically review and assess the performance of all published models that predicted development of COPD. A search was conducted to identify studies that developed a prediction model for COPD development. The Checklist for Critical Appraisal and Data Extraction for Systematic Reviews of Prediction Modelling Studies was followed when extracting data and appraising the selected studies. Of the 4,481 records identified, 30 articles were selected for full-text review, and only four of these were eligible to be included in the review. The only consistent predictor across all four models was a measure of smoking. Sex and age were used in most models; however, other factors varied widely. Two of the models had good ability to discriminate between people who were correctly or incorrectly classified as at risk of developing COPD. Overall none of the models were particularly useful in accurately predicting future risk of COPD, nor were they good at ruling out future risk of COPD. Further studies are needed to develop new prediction models and robustly validate them in external cohorts.

Exposure to low concentrations of air pollutants and adverse birth outcomes in Brisbane, Australia, 2003-2013

BACKGROUND

It's unclear whether exposures to low-level air pollution have adverse effects on birth outcomes, and which trimester-specific pregnant exposure is sensitive.

OBJECTIVES

To investigate the effects of maternal exposure during each trimester and the whole pregnancy to particles with aerodynamic diameter<2.5μm (PM_2.5), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃) on preterm birth (PTB) and low birth weight (LBW).

METHODS

Daily data on birth records, air quality, and weather conditions were collected in Brisbane, Australia during 2003-2013. Mean concentrations of air pollutants were calculated for each trimester of pregnancy. Cox proportional hazards models were used to examine the associations between air pollution and birth outcomes. Multi-pollutant models and stratified analyses by ambient temperature were performed.

RESULTS

Exposures to PM_2.5, SO₂, NO₂, and O₃ during the whole pregnancy were associated with increased risk of PTB [IQR HRs (hazard ratios with an interquartile range increase in air pollutants) and 95% confidence intervals (CIs): 1.05 (1.02, 1.08), 1.12 (1.09, 1.16), 1.07 (1.01, 1.13), and 1.13 (1.10, 1.16), respectively] and LBW [IQR HRs and 95% CIs: 1.06 (1.02, 1.10), 1.12 (1.08, 1.16), 1.11 (1.03, 1.18), and 1.13 (1.09, 1.17), respectively]. Highest HRs were observed during trimester 3, and lowest in trimester 1. For each air pollutant, stronger effects on PTB and LBW were present for exposure to low and moderate temperatures than exposure to high ambient temperature.

CONCLUSIONS

Exposures to low-level air pollutants are related to adverse birth outcomes. More effective policies for air quality control could contribute to improving neonatal health.

Traffic related air pollution and development and persistence of asthma and low lung function

BACKGROUND AND AIMS

Traffic Related Air Pollution (TRAP) exposure is known to exacerbate existing respiratory diseases. We investigated longer term effects of TRAP exposure for individuals with or without existing asthma, and with or without lower lung function.

METHODS

Associations between TRAP exposure and asthma (n = 689) and lung function (n = 599) were investigated in the prospective Tasmanian Longitudinal Health Study (TAHS). TRAP exposure at age 45 years was measured using two methods based on residential address: mean annual NO₂ exposure; and distance to nearest major road. Adjusted multinomial logistic regression was used to model the association between exposure to TRAP at 45 years and changes in asthma and lung function, using three follow ups of TAHS (45, 50 and 53 years).

RESULTS

For those who never had asthma by 45, living <200 m from a major road was associated with increased odds of new asthma that persisted from 50 to 53 years (adjusted Odds Ratio [aOR] 5.20; 95% CI 1.07, 25.4). Asthmatic participants at 45 had an increased risk of persistent asthma up to 53 years if they were living <200 m from a major road, compared with asthmatic participants living >200 m from a major road (aOR = 5.21; 95% CI 1.54, 17.6).

CONCLUSION

For middle aged adults, living <200 m for a major road (a marker of TRAP exposure) influences both the development and persistence of asthma. These findings have public health implications for asthma prevention strategies in primary and secondary settings.

Representativeness and repeatability of microenvironmental personal and head exposures to radio-frequency electromagnetic fields

The aims of this study were to: i) investigate the repeatability and representativeness of personal radio frequency-electromagnetic fields (RF-EMFs) exposure measurements, across different microenvironments, ii) perform simultaneous evaluations of personal RF-EMF exposures for the whole body and the head, iii) validate the data obtained with a head-worn personal distributed exposimeter (PDE) against those obtained with an on-body worn personal exposimeter (PEM). Data on personal and head RF-EMF exposures were collected by performing measurements across 15 microenvironments in Melbourne, Australia. A body-worn PEM and a head-worn PDE were used for measuring body and head exposures, respectively. The summary statistics obtained for total RF-EMF exposure showed a high representativeness (r² > 0.66 for two paths in the same area) and a high repeatability over time (r² > 0.87 for repetitions of the same path). The median head exposure in the 900MHz downlink band ranged between 0.06V/m and 0.31V/m. The results obtained during simultaneous measurements using the two devices showed high correlations (0.42 < r² < 0.94). The highest mean total RF-EMF exposure was measured in Melbourne's central business district (0.89V/m), whereas the lowest mean total exposure was measured in a suburban residential area (0.05V/m). This study shows that personal RF-EMF microenvironmental measurements in multiple microenvironments have high representativeness and repeatability over time. The personal RF-EMF exposure levels (i.e. body and head exposures) demonstrated moderate to high correlations.

Childhood measles contributes to post-bronchodilator airflow obstruction in middle-aged adults: A cohort study

BACKGROUND AND OBJECTIVE

Chronic obstructive pulmonary disease (COPD) has potential origins in childhood but an association between childhood measles and post-bronchodilator (BD) airflow obstruction (AO) has not yet been shown. We investigated whether childhood measles contributed to post-BD AO through interactions with asthma and/or smoking in a non-immunized middle-aged population.

METHODS

The population-based Tasmanian Longitudinal Health Study (TAHS) cohort born in 1961 (n = 8583) underwent spirometry in 1968 before immunization was introduced. A history of childhood measles infection was obtained from school medical records. During the fifth decade follow-up (n = 5729 responses), a subgroup underwent further lung function measurements (n = 1389). Relevant main associations and interactions by asthma and/or smoking on post-BD forced expiratory volume in 1 s/forced vital capacity (FEV₁ /FVC; continuous variable) and AO (FEV₁ /FVC < lower limit of normal) were estimated by multiple regression.

RESULTS

Sixty-nine percent (n = 950) had a history of childhood measles. Childhood measles augmented the combined adverse effect of current clinical asthma and smoking at least 10 pack-years on post-BD FEV₁ /FVC ratio in middle age (z-score: -0.70 (95% CI: -1.1 to -0.3) vs -1.36 (-1.6 to -1.1), three-way interaction: P = 0.009), especially for those with childhood-onset asthma. For never- and ever-smokers of <10 pack-years who had current asthma symptoms, compared with those without childhood measles, paradoxically, the odds for post-BD AO was not significant in the presence of childhood measles (OR: 12.0 (95% CI: 3.4-42) vs 2.17 (0.9-5.3)).

CONCLUSION

Childhood measles infection appears to compound the associations between smoking, current asthma and post-BD AO. Differences between asthma subgroups provide further insight into the complex aetiology of obstructive lung diseases for middle-aged adults.