Surveillance of acute health effects of air pollution in Mexico City.
BACKGROUND
A unique, active, timely, low-cost surveillance system for the metropolitan area of Mexico City was established in the mid-1990s.


METHODS
The system obtained upper and lower respiratory tract symptoms and eye symptoms from daily interviews for a systematic sample of the general nonhospitalized population living within a 2-km radius of air pollution monitors during 1996-1997.


RESULTS
Ozone increments (10 ppb) were associated with upper respiratory symptoms (odds ratio [OR] = 1.003; 95% confidence interval [CI] = 1.002-1.004) and ocular symptoms indicators (OR = 1.005; CI = 1.004-1.007), and with a higher risk of lower respiratory symptoms indicator among nonsmokers (OR = 1.003; CI = 1.002-1.005). Increases in relative humidity reduced the risk of increments of sulfur dioxide on the 3 acute health indicators. Association of PM10 with health indicators varied among the 5 regions. During emergency episodes, symptoms increased sharply when ozone reached 281 ppb, a finding that resulted in a change in the ozone criteria for emergency declaration from 294 to 281 ppb.


CONCLUSIONS
This system has been low cost, timely, and useful for local decision making.
D000293:Adolescent; D000328:Adult; D000397:Air Pollution; D003430:Cross-Sectional Studies; D004782:Environmental Health; D005260:Female; D006306:Health Surveys; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008297:Male; D008800:Mexico; D012140:Respiratory Tract Diseases / Q000209:etiology