Effects of urban air pollutants on emergency visits for childhood asthma in Mexico City

Am J Epidemiol. 1995 Mar 15;141(6):546-53. doi: 10.1093/oxfordjournals.aje.a117470.


The metropolitan area of Mexico City, Mexico, has serious air pollution problems. Although air contaminants may contribute to clinical asthma, there are at present no data on the relation between air pollution exposure and childhood asthma in Mexico City. The authors reviewed data on emergency visits from January to June 1990 at one major pediatric hospital in Mexico City. They used a Poisson regression model to study the relation between the number of daily emergency visits for asthma and air pollutant levels. The levels of ozone and sulfur dioxide-exposure were significantly associated with the number of emergency visits for asthma. After adjustment for potential confounding factors, the multivariate regression model predicted that an increase of 50 ppb in the 1-hour maximum ozone level would lead to a 43% increase in the number of emergency visits for asthma on the following day. Exposure to high ozone levels (> 110 ppb) for 2 consecutive days increased the number of asthma-related emergency visits by 68 percent. The results of this study suggest that ozone exposure is positively associated with the number of children's emergency visits for asthma in Mexico City.

PIP: A retrospective analysis of records of emergency visits during January-June 1990 at the Hospital Infantil de Mexico Federico Gomez in the northern section of Mexico City was conducted to examine the association between the 395 children's (16 years) emergency visits for asthma (2.5% of all emergency visits) and daily levels of different air pollutants. Most emergency visits for asthma (67%) included children aged less than 5. The mean ozone daily one-hour maximum level was 90 ppb (range: 10-250 ppb). The ozone level exceeded the Mexican ozone standard (110 ppb) on 49 days (28%). Concentrations of ozone and sulfur dioxide exposure were linked to the number of emergency visits for asthma (p = 0.001 for 1-hour maximum with 1-day lag and p = 0.07 for 1-hour maximum on same day). When the researchers controlled for confounding factors, they found that a rise in the ozone level of 50 ppb was related to a 43% increase in the number of emergency visits for asthma with a one-day lag period. 133% of these visits were made after two consecutive days of ozone levels of at least 110 ppb. Exposure to such high ozone levels increased the number of emergency visits for asthma by 68%. These findings demonstrate a positive relationship between ozone exposure and the number of children living in Mexico City who were treated for asthma. In fact, they suggest that cumulative exposure to ozone strengthens this association.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Air Pollutants / adverse effects*
  • Asthma / chemically induced*
  • Asthma / epidemiology
  • Bronchiolitis / chemically induced*
  • Bronchiolitis / epidemiology
  • Child
  • Child, Preschool
  • Emergency Service, Hospital / statistics & numerical data*
  • Female
  • Humans
  • Likelihood Functions
  • Male
  • Mexico / epidemiology
  • Ozone / adverse effects
  • Ozone / analysis
  • Poisson Distribution
  • Sulfur Dioxide / adverse effects
  • Sulfur Dioxide / analysis
  • Time Factors
  • Urban Population*


  • Air Pollutants
  • Sulfur Dioxide
  • Ozone