Iranian Journal of

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Background & Objectives: Recent evidence suggests that long-term exposure to air pollution contributes to progression of atherosclerosis and the risk of cardiac morbidity and mortality short-term exposure may also lead to thrombosis and acute ischemic events. To evaluate the relation between the levels of major air pollutants (CO and PM10) and hospital admission for acute coronary syndrome (ACS) in Tehran, we performed a case-crossover design and checked whether individual characteristics act as effect modifiers.
Methods: We selected 250 Tehran residents who had been hospitalized with an acute coronary syndrome from 4th of April to 10th of June, 2007. The following individual data were gathered: sex, age, date of hospitalization, and coexisting illnesses (hypertension, diabetes). Daily air pollution data were taken from the Air Quality Control Center. Temperature, humidity, stress, physical activity and weekend days were treated as confounding variables, and a conditional logistic regression model was used for statistical analysis.
Results: We found a positive association between ACS and average 24-hour CO levels. The OR for each unit increase of the average 24-hour CO was 1.18 (95%CI: 1.03-1.34). The relation between ACS and 24-hour average PM10 did not reach statistical significance (OR for average 24-hour PM10 was 1.005, 95%CI: 0.99-1.01). The association between ACS and 24-hour average CO tended to be stronger in women (OR=1.68 for each unit increase, 95%CI: 1.25-2.26). The relation between 24-hour average PM10 and ACS did not change across the layers of the effect modifiers.
Conclusions: The results suggest that an increase in average 24-hour CO levels will augment the risk of ACS, and the effect is stronger in females. On the other hand, we were unable to document an association between ACS and average 24-hour PM10 levels.

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The case-crossover design was developed in the early 1990s to study the effects of transient, short-term exposures on the risk of acute events such as myocardial infarction. To estimate relative risk, the exposure frequency during a period just before outcome onset (hazard period) is compared with exposure frequency during control time(s) in that person rather than in a control. One or more "control times" are supplied by each of the cases themselves to control for confounding by constant characteristics and self-confounding between the trigger's acute and chronic effects. In the analysis of case-crossover studies, exposure frequency in the hazard period is compared with the control period or the individual's usual frequency of exposure. The design has been used frequently for heart diseases, injuries and air pollution epidemiology. This review article looks at published case-crossover studies and is intended to help the reader gain a better understanding of the strengths and limitations of the case-crossover design in studying the epidemiology of injuries and air pollution.

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London fog obviously revealed the role of air pollution in increasing mortality and morbidity rates associated with this phenomenon but several studies in the 70’s and 80’s couldn’t establish sufficient link between air pollution and death. In the 1990’s, time series studies conducted in a different locations, showed that air pollution levels, even at lower concentrations, were associated with increased rates of morbidity and mortality in several cities in all over the world. Since several studies have been designed for investigating the association between air pollution and health outcomes in recent years with controversial conclusions, this article reviews the latest studies in this field. We also will mention main strengths and weaknesses of epidemiological designs including time-series, case-crossover, cross sectional, panel and cohort studies in indoor and outdoor air pollution epidemiology.

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Background & Objectives: Some case-report studies in Iran showed probable association between anthracosis and smoke exposure due to baking homemade bread, population. Therefore we estimated the population attributable fraction (PAF) for this probable association in Iranian population.
Methods: A hospital-based case-control study, including 83 anthracotic subjects (cases) with 72 controls from surgical ward which were matched by age, conducted in Imam Khomeini hospital in Tehran (From September 2009 to December 2010). Patients in both case and control groups were interviewed according to "American Thoracic Society" guideline. Exposure to smoke was considered both as a binary and continuous variable (number of years being exposed to smoke) and the population attributable fraction (PAF) were estimated due to smoke exposure.
Results: Univariate analysis showed that exposure to smoke as binary variables, age and occupation exposure to dust and education were associated with anthracosis. After Adjusting, only smoke exposure (OR: 3.35, 95% CI: 1.49-7.55) remain significant. Univariate logistic regression model showed exposure to smoke as continuous variable has significant association with anthracosis. In multiple logistic  model only duration (years) of smoke exposure remained significant (OR: 1.05, 95%CI: 1.01-1.09). PAF due to smoke exposure estimated approximately 48% in our population.
Conclusion: Based on the findings of this study, it could be concluded that approximately half of the anthracotic cases are attributed to smoke exposure.

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