The association between different timeframes of air pollution exposure and COVID-19 incidence, morbidity and mortality in German counties in 2020

Abstract

Background: Ambient air pollution is a known risk factor for several chronic health conditions, including pulmonary dysfunction. In recent years, studies have shown a positive association between exposure to air pollutants and the incidence, morbidity, and mortality of a COVID-19 infection, however the time period for which air pollution exposure is most relevant for the COVID-19 outcome is still not defined. The aim of this study was to analyze the difference in association when varying the time period of air pollution exposure considered on COVID-19 infection within the same cohort during the first wave of the pandemic in 2020.

Methods: We conducted a cross-sectional study analyzing the association between long- (10- and 2-years) and short-term (28 days, 7 days, and 2 days) exposure to NO₂ and PM_2.5 on SARS-CoV-2 incidence, morbidity, and mortality at the level of county during the first outbreak of the pandemic in spring 2020. Health data were extracted from the German national public health institute (Robert-Koch-Institute) and from the German Interdisciplinary Association for Intensive Care and Emergency Medicine. Air pollution data were taken from the APExpose dataset (version 2.0). We used negative binomial models, including adjustment for risk factors (age, sex, days since first COVID-19 case, population density, socio-economic and health parameters).

Results: We found that PM_2.5 and NO₂ exposure 28 days before COVID-19 infection had the highest association with infection, morbidity as well as mortality, as compared to long-term or short-term (2 or 7 days) air pollutant exposure. A 1 μg/m³ increase in PM_2.5 was associated with a 31.7% increase in incidence, a 20.6% need for ICU treatment, a 23.1% need for mechanical ventilation, and a 55.3% increase in mortality; an increase of 1 μg/m³ of NO₂ was associated with an increase for all outcomes by 25.2 - 29.4%.

Conclusions: Our findings show a positive association between PM_2.5 and NO₂ exposure and the clinical course of a SARS-CoV2 infection, with the strongest association to 28 days of exposure to air pollution. This finding provides an indication as to the primary underlying pathophysiology, and can therefore help to improve the resilience of societies by implementing adequate measures to reduce the air pollutant impact on health outcomes.

Trial registration: Not applicable.

Keywords: Air pollution; COVID-19; Intensive care medicine; Long-term exposure; Mechanical ventilation; Mortality; Nitrogen dioxide; Particulate matter; SARS-CoV-2; Short-term exposure.

Fig. 1

Air pollutant exposure can increase the vulnerability towards adverse COVID-19 health outcomes. By long-term (10 to 2 years) exposure the induction of chronic diseases are known risk factors for COVID-19 infection, morbidity and mortality. In the short-term (28 to 7 days) exposure, air pollutants might increase COVID-19 vulnerability by inducing an inflammatory response in the lung tissue and the human body. Finally, as SARS-CoV2 can adhere to small particulate matter in the air, this might also increase COVID-19 incidence within very short-term exposure up to 48 h

Fig. 2

COVID-19 disease parameters per county for the period April 16th to May 16th 2020. Darker colors indicate higher values. Counties with missing data are marked in grey

Fig. 3

NO₂-levels and PM_2.5-levels per county as mean of the annual means for the period 16.04. – 16.05.2020 and over the last 10 years from 2010–2019. A) NO₂-levels for the period 16.04. – 16.05.2020; B) PM_2.5-levels for the period 16.04. – 16.05.2020; C) NO₂-levels for the period 2010–2019; D) PM_2.5-levels for the period 2010–2019. Darker colors indicate higher values

Fig. 4

Outcome parameters and NO₂-levels and PM_2.5-levels over time. A) Incidence and mortality and NO₂-levels and PM_2.5-levels over time in March – May 2020. Pollution variables for a given date are given as average of the previous 48 h. The dashed colored lines are WHO-recommended thresholds annual average levels of NO₂ and PM_2.5. The pink line indicates the period for which data is available in the DIVI-register. B) Patient-days on ICU and on mechanical ventilation and NO₂-levels and PM_2.5-levels over time in April – May 2020. The dashed colored lines are WHO-recommended thresholds for annual average levels of NO₂ and PM_2.5

Fig. 5

Effect estimates for the association of A) NO₂ and B) PM_2.5 on COVID-19 outcomes. Bars indicate 95% confidence intervals. Each estimate is derived from a separate, single-pollutant model adjusted to confounders (age over 65 years, sex, social depravation, population density and days between the first reported COVID-19 case and March 1.^st)