Daily diaries of respiratory symptoms and air pollution: methodological issues and results

Air pollution and respiratory status in asthmatic children: hints for a locally based preventive strategy. AIRE study

Respiratory health effects of short-term exposure to ambient air pollution have been examined in 120 'asthma-like' school-aged children in some areas of Emilia-Romagna (urban-industrial and rural area). They kept a daily diary, through 12 weeks, for respiratory symptoms, PEF measurements, drug consumption and daily activity. The average daily concentrations of air pollutants in the same period (TSP, NO2, CO, PM2.5) were higher in the industrial than the rural area. Asthma was diagnosed in 77% of cases, 85% of subjects took medical treatments for respiratory disease in the last year and 90% used medicine for respiratory diseases. Significantly lower variations in PEF, between morning and evening, were observed in the rural area, considering only the asthmatic or cough subsets of children. Symptom prevalence was higher in the urban-industrial area than the rural area; the most frequent symptoms were cough, phlegm and stuffed nose. The two area populations are homogeneous in individual features, family susceptibility, passive smoking exposure and atopy. The differences observed in the frequency of daily reported symptoms could be attributed to external situations like the different reported exposures to pollutants. Although most analyses revealed non-significant associations, panel analysis showed a significant statistical risk for the cough and phlegm group by an increase of 10 microg of TSP (RR 1.0017, 95% CI: 1.0002-1.0033) in the entire group. In the urban-industrial panel we observed a significant association between cough and phlegm together and PM2.5 (RR 1.0044, 95% CI: 1.0011-1.0077). The results of this investigation should be used in orienting local political decisions.

Particulate air pollution and panel studies in children: a systematic review

BACKGROUND

Panel studies have been used to investigate the short term effects of outdoor particulate air pollution across a wide range of environmental settings.

AIMS

To systematically review the results of such studies in children, estimate summary measures of effect, and investigate potential sources of heterogeneity.

METHODS

Studies were identified by searching electronic databases to June 2002, including those where outcomes and particulate level measurements were made at least daily for > or =8 weeks, and analysed using an appropriate regression model. Study results were compared using forest plots, and fixed and random effects summary effect estimates obtained. Publication bias was considered using a funnel plot.

RESULTS

Twenty two studies were identified, all except two reporting PM10 (24 hour mean) >50 microg x m(-3). Reported effects of PM10 on PEF were widely spread and smaller than those for PM2.5 (fixed effects summary: -0.012 v -0.063 l x min(-1) per microg x m(-3) rise). A similar pattern was evident for symptoms. Random effects models produced larger estimates. Overall, in between-study comparisons, panels of children with diagnosed asthma or pre-existing respiratory symptoms appeared less affected by PM10 levels than those without, and effect estimates were larger where studies were conducted in higher ozone conditions. Larger PM10 effect estimates were obtained from studies using generalised estimating equations to model autocorrelation and where results were derived by pooling subject specific regression coefficients. A funnel plot of PM10 results for PEF was markedly asymmetrical.

CONCLUSIONS

The majority of identified studies indicate an adverse effect of particulate air pollution that is greater for PM2.5 than PM10. However, results show considerable heterogeneity and there is evidence consistent with publication bias, so limited confidence may be placed on summary estimates of effect. The possibility of interaction between particle and ozone effects merits further investigation, as does variability due to analytical differences that alter the interpretation of final estimates.

Experimental strategies for research on multiple chemical sensitivity

Skepticism about the validity of the multiple chemical sensitivity (MCS) syndrome stems in part from the lack of supporting experimental data. Performing the relevant experiments requires investigators to take account of broad variations in sensitivity and the need to establish reproducibility. The research approach best suited for MCS studies is the single-subject design. In contrast with conventional group designs, such designs emphasize repeated observations on individual subjects. Repeated observations of this kind constitute a time series in which successive measurements are serially or autocorrelated. One statistical method that bypasses the serial correlation problem is randomization tests. Explicit time series analyses take account of this aspect and can correct for it to determine the impact of an intervention such as a chemical exposure.

Low-level air pollution and hospital admissions for cardiac and cerebrovascular diseases in Helsinki

OBJECTIVES

This study investigated whether low concentrations of ambient air pollutants are associated with hospital admissions for ischemic cardiac and cerebrovascular diseases.

METHODS

Associations between daily concentrations of sulfur dioxide, nitric oxide, nitrogen dioxide, ozone, and particulates and daily hospital admissions due to ischemic cardiac and cerebrovascular diseases were studied in Helsinki, Finland, 1987 through 1989. The regression analyses controlled for weather, day of the week, season, long-term trends, and influenza epidemics.

RESULTS

Admissions via emergency rooms due to ischemic cardiac diseases (n = 7005) were significantly associated with the prevailing levels of nitric oxide and ozone, and those due to cerebrovascular diseases (n = 3737) were associated with nitrogen dioxide; these levels were only moderate. Long-term transient myocardial ischemic attacks were related to particulates, and short-term ischemic attacks were related to nitrogen dioxide.

CONCLUSIONS

Symptoms of ischemic cardiac and cerebrovascular diseases may be provoked by pollutants in concentrations lower than those given as guidelines in many countries and lower than previously shown.

Asthma and ambient air pollution in Helsinki

OBJECTIVE

To study whether ambient air levels of sulphur dioxide (SO2), nitrogen dioxide (NO2), total suspended particulates (TSP), and ozone (O3) affect the number of hospital admissions for asthma.

DESIGN

The associations between the daily number of admissions and air pollutants were analysed with Poisson regression, taking into account potential confounding factors by using the standardised protocol of the APHEA project.

SETTING

Helsinki, Finland, 1987-89.

PATIENTS AND MEASUREMENTS

Patients admitted to hospitals through emergency rooms because of asthma (n = 2421). The daily mean concentration was 13-25 micrograms/m3 for SO2, 33-41 micrograms/m3 for NO2, 19-41 micrograms/m3 for O3, and 58-109 micrograms/m3 for TSP during the different seasons. Values are means for various stations. The daily mean temperature during the three year period was +5.4 degrees C (range -37-27 degrees C).

MAIN RESULTS

Positive associations with admissions were observed for O3 levels in all children under 14 years, and for SO2 levels in 15-64 year olds and among those older than 64. Significant associations were also seen between admissions for digestive tract diseases (the control) and O3 levels. This suggests that the modelling, which proved to be problematic, was unsatisfactory, or it may be a statistical coincidence. A rise in temperature was associated with a low number of admissions for asthma among 0-14 year olds and among 15-64 year olds, whereas humidity did not have a significant effect on the number of admissions.

CONCLUSIONS

It is possible than even low level pollution may increase hospital admissions for asthma. However, definitive conclusions will be justified only after meta-analysis comprising several studies. The methodology was seen to have a strong effect on the results and standardised methods, possibly differing from those for the study concerning mortality, are needed to investigate the association between morbidity and ambient air pollutants.

Effects of air pollution on symptoms and peak expiratory flow measurements in subjects with obstructive airways disease

BACKGROUND

Evidence from laboratory studies suggests that air pollution can produce bronchoconstriction and respiratory symptoms in selected subjects, but the relevance of these findings to exposure to natural pollution is unclear. This study was performed to determine whether air pollution at typical levels found in the UK has demonstrable effects on respiratory function and symptoms in subjects with airways disease.

METHODS

Seventy five adult patients with diagnoses of asthma or chronic obstructive pulmonary disease (COPD) were studied for a period of four weeks during which they kept records of their peak expiratory flow (PEF) rates, symptoms (wheeze, dyspnoea, cough, throat and eye irritation), and bronchodilator use. Thirty six patients in whom the provocative dose of methacholine causing a 20% fall in FEV1 was below 12.25 mumol were classified as reactors. Ambient air pollution was measured with absorption spectroscopy.

RESULTS

There were modest but significant increases in PEF variability, bronchodilator use, and wheeze with increasing sulphur dioxide levels; bronchodilator use, dyspnoea, eye irritation, and minimum PEF readings were related to ozone levels. In the subgroup of reactors falls in mean and minimum peak flow and increases in wheeze, dyspnoea, and bronchodilator use were associated with increases in levels of both sulphur dioxide and ozone. Some associations were seen with pollution levels on the same day, but for others the pollution effects appeared to be delayed by 24 or 48 hours. Pollution levels did not breach the WHO guide levels during the course of the study.

CONCLUSIONS

Increases in environmental levels of ozone and sulphur dioxide are associated with adverse changes in peak flow measurements and both ocular and respiratory symptoms in subjects with obstructive airways disease. Although the peak flow and symptom changes were modest, they occurred at pollution levels below current WHO guide levels.

Assessment of health effects in epidemiologic studies of air pollution

As we increasingly recognize the complexity of the pollutants in indoor and outdoor microenvironments, a broad array of inhaled mixtures has assumed scientific, public health, and regulatory importance. Few adverse effects of environmental pollutants are specific, that is, uniquely associated with a single agent; the adverse effects that might be considered in an investigation of the consequences of exposure to an inhaled complex mixture are generally nonspecific. In the context of this paper, we will refer to binary mixtures as complex, though we realize that a more precise definition of complexity would restrict the term to mixtures of three or more constituents. Their causes potentially include not only pollutant exposures through the medium of inhaled air but other environmental agents, such as infectious organisms and radiation, and inherent characteristics of the exposed persons, such as atopy. We review the outcome measures that have been used in epidemiologic studies of the health effects of single pollutants and complex mixtures. Some of these outcome measures have been carefully standardized, whereas others need similar standardization and modification to improve sensitivity and specificity for investigating the health effects of air pollution.

Assessment of health effects in epidemiologic studies of air pollution

As we increasingly recognize the complexity of the pollutants in indoor and outdoor microenvironments, a broad array of inhaled mixtures has assumed scientific, public health, and regulatory importance. Few adverse effects of environmental pollutants are specific, that is, uniquely associated with a single agent; the adverse effects that might be considered in an investigation of the consequences of exposure to an inhaled complex mixture are generally nonspecific. In the context of this paper, we will refer to binary mixtures as complex, though we realize that a more precise definition of complexity would restrict the term to mixtures of three or more constituents. Their causes potentially include not only pollutant exposures through the medium of inhaled air but other environmental agents, such as infectious organisms and radiation, and inherent characteristics of the exposed persons, such as atopy. We review the outcome measures that have been used in epidemiologic studies of the health effects of single pollutants and complex mixtures. Some of these outcome measures have been carefully standardized, whereas others need similar standardization and modification to improve sensitivity and specificity for investigating the health effects of air pollution.