Development of Chronic Productive Cough as Associated with Long-Term Ambient Inhalable Particulate Pollutants (PM₁₀) in Nonsmoking Adults: The AHSMOG Study

Abstract

Standardized respiratory symptom questionnaires were completed by 3091 nonsmoking California Seventh-Day Adventists in 1977, 1987, and 1992. Ambient concentrations of air pollutants estimated included total suspended particulates (TSP), 1973–1987; particulates ⩽10 μm in diameter (PM₁₀), indirectly estimated from TSP, 1973–1987, and directly estimated from monitored PM₁₀, 1987–1992; suspended sulfates, 1977–1992; sulfur dioxide, 1973–1992; and 8-hour average of ozone, 1973–1992. Adjustments to ambient concentrations have been made for time spent indoors. Chronic bronchitis was defined as cough only (cough type) or with sputum production (chronic productive cough) on most days, for at least 3 months/year, for 2 years or more. Using indirect estimates of PM₁₀ prior to 1987 and direct estimates after 1987, multiple logistic regression models adjusting for covariates have been used to study development of chronic bronchitis (235 new cases) and chronic productive cough (169 new cases) between 1977 and 1992. For chronic productive cough, gender-specific analyses indicated similar effects of PM₁₀ and covariates for both genders. Hence, a pooled analysis was conducted using gender as a covariate. The relative risk for developing chronic productive cough was 1.25 (95% confidence interval: 1.04, 1.51; p = 0.02) for an interquartile range increase of 41 days/year in excess of 100 μg/m³ of PM₁₀, while no association was found with ozone, suspended sulfates, or sulfur dioxide. Statistically significant associations were also seen for development of chronic productive cough for days when PM₁₀ daily mean concentration exceeded 80 μg/m³. The estimated relative risk for developing definite symptoms of overall chronic bronchitis (either cough or sputum type) in 1992 as associated with an interquartile range increase of 41 days/year when PM₁₀ concentrations exceeded 100 μg/m³ was 1.33 (95% confidence interval: 1.14, 1.55; p = 0.0005).