# Assessing the risks of short-term exposure to ambient air pollutants on COVID-19 hospitalizations in Tehran, Iran: a time-stratified case-crossover approach

## TL;DR

This study found that exposure to certain air pollutants like fine particulate matter and ozone increases the risk of being hospitalized with COVID-19 in Tehran.

## Contribution

The study uses a time-stratified case-crossover approach to assess the impact of short-term air pollution exposure on COVID-19 hospitalizations in Tehran.

## Key findings

- Exposure to fine particulate matter, nitrogen dioxide, and ozone was significantly associated with increased COVID-19 hospitalizations.
- Ozone and nitrogen dioxide were linked to the highest number of attributable hospitalizations (6,000 and 3,300 cases respectively).
- Coarse particulate matter showed no significant association with hospitalizations.

## Abstract

This study aimed to evaluate the impact of both cumulative and non-cumulative exposure to air pollutants on hospitalizations due to Coronavirus Disease 2019 (COVID-19) in Tehran.

A time-stratified case-crossover approach was employed to estimate the relative risks and assess the attributable fraction and attributable number of COVID-19 hospitalizations associated with air pollution exposure. Data on hospitalizations were collected from a teaching hospital in Tehran between March 20, 2020, and September 20, 2022, and were categorized by gender and age. Air pollution data including fine particulate matter (particles with a diameter less than 2.5 micrometers), nitrogen dioxide, sulfur dioxide, coarse particulate matter (particles with a diameter less than 10 micrometers), ozone, and carbon monoxide were obtained from the Environmental Protection and Air Quality Control Organization of Tehran. Quasi-Poisson conditional regression and distributed lag non-linear models were applied to estimate the relative risk of hospitalizations associated with pollutant exposure.

The findings indicate a significant association between exposure to fine particulate matter, nitrogen dioxide, and ozone with increased COVID-19 hospitalizations. The estimated relative risks for hospitalizations were 1.36 (95% confidence interval: 1.15–1.62), 1.17 (95% confidence interval: 1.07–1.29), and 1.37 (95% confidence interval, 1.19–1.58), respectively. No significant association was observed between coarse particulate matter exposure and hospitalizations. The number of hospitalizations attributed to ozone (6,000 cases) and nitrogen dioxide (3,300 cases) exceeded those associated with other pollutants.

This study highlights the impact of air pollution on increased hospitalization risk for COVID-19. These findings underscore the urgent need for health authorities to implement stringent air quality regulations and pollution control measures to mitigate the adverse health effects of air pollution.