# Presentation: 917181

## The Association Between Ozone and Mortality: What do we know and when did we know it?

**Bart Ostro, Ph.D., Chief**
**Air Pollution Epidemiology Unit**
**California EPA**

## Overview

**When did we know there was an association?**
**What is the current evidence?**
**How certain are we?**

**Overview**

## When did we know it? 

**Mid 1950s, LA ozone peak levels of 0.68 ppm (vs standard of 0.12 ppm) observed**
**1956 survey of LA physicians reports: **
**95% recognized the existence of a "smog complex" involving irritation of the respiratory tract, chest pains, and cough**
**68% believe that patients with cardiac diseases are more susceptible to smog than healthy adults**** **
**First mortality studies in 1950s and 60s – weak methods, results unclear**
**Ozone research in 1975 to early 1990s:  Focus on controlled exposure studies **

**Early 1990s:  a few time series studies of mortality and hospitalization plus panel studies on asthmatics**
**Ozone often viewed only as potential confounder in PM studies **
**Some reawakening in late 90s**
**Heightened interest in Europe**
**Methodological developments**
**Several meta analyses and NMMAPS **

## What is the current evidence? 

**Evidence for mortality based on two types of epidemiological study designs:**
**Time Series studies**** examine daily counts of mortality for a given city over several years**
**Cohort studies**** examine individuals over a long period of time across many cities**

## What is the Current Evidence? 

**Multiple studies showing ****morbidity ****associated with ozone**
**Controlled human studies show effects on lung function, symptoms and inflammation  **
**Epidemiologic studies show effects on:**
**Hospital admissions for respiratory disease**
**ER visits for asthma**
**Exacerbation of asthma**
**New cases of asthma (with exercise)**
**School and work loss**
**Respiratory symptoms**

## What is the Current Evidence?

**Multiple studies showing ****mortality**** but results not totally consistent **
**Many challenges**
**Concern for effects of temperature**
**Summer only effects? **
**Confounding by PM10?**
**Measuring exposure to ozone**
**Difficulty in modeling long cycles of mortality by season**

## Cyclical Patterns of Mortality and Ozone in LA 1999-2002

- 0

- 50

- 100

- 150

- 200

- 250

- 0

- 500

- 1000

- 1500

- Time

**mortality**

**Ozone **
**(8-hr,ppb)**

## Recent Reanalysis of Mortality and Ozone from NMMAPS is Compelling(Bell et al., 2004)

**Involves 95 cities, 1987-2000**
**Associations found between ozone and total and cardiopulmonary mortality**
**Similar effects for:**
**	****	****o 55 cities with full years of data**
**	****	****o Warm season only**
**	****	**** ****o All 95 cities**

## NMMAPS 

**Robust to inclusion of PM10 in the model and exclusion of high temperature days**
**Similar effects among ages < 65, 65-74, 75+**

## Ozone study details

**Ozone study details**

## 1. WHO (2004)                  5. Stieb et al. (2003)       9. Levy et al. (2001)

**1. WHO (2004)                  5. Stieb et al. (2003)       9. Levy et al. (2001)**
**2. WHO (2004)                  6. Bell et al. (2004)        10. Gryparis et al. (2004)**
**3. Thurston & Ito (2001)  7. Bell et al. (2004)        11. Gryparis et al. (2004)**
**4. Thurston & Ito (2001)  8. Levy et al. (2001)**

## Results from Prospective Cohort Studies

**Analysis of American Cancer Society (ACS) data has examined effects of long-term exposure to PM and other pollutants**
**Study subjects followed up to 16 years**
**Analyses control for individual-level risk factors for mortality (e.g., age, gender, weight, tobacco and alcohol use, occupational exposure)**

**Associations found between PM2.5 and sulfate and both cardiopulmonary mortality and lung cancer (Pope et al., 1995, 2002)**
**Hint of an association (p = 0.07) between long-term summertime ozone and cardiopulmonary mortality**
**If true, there may be even larger effects from exposure to ozone**

## Possible Mechanisms

-  Pulmonary i**nflammation**
** ****Impacts on heart rate-pressure**
** ****Impacts on gas exchange region making heart work harder**

**Notes:**
May affect pulmonary defense against infection

## How Certain Are We?

**Associations appear plausible given:**
**Potential mechanisms **
**Demonstrated effects on hospitalization and ER visits for asthma**
**Meta analyses and NMMAPS**
**Better control for weather seems to increase effect size**
**	****	****	****	**

**BUT**

## How Certain Are We?

**Rigorous sensitivity analysis still necessary for treatment  of weather and season**
**Relative risk is small and sensitive to models used **
**Heterogeneity in response observed including negative studies**