Exposure to air pollutants is a major aggravator of respiratory diseases, and it’s no different for COVID-19.

The severity of COVID-19 infection is known to vary by age, comorbidity history, and more. Disease severity can even vary by geographical location, leading investigators to research the link between environmental factors and COVID-19 susceptibility, severity, and outcome.

The study, published in the European Respiratory Journal, specifically examined whether exposure to air pollution and accumulated black carbon particles in blood were correlated with COVID-19 disease severity, need for intensive care, and duration of hospitalization.

Between May 2020-March 2021, the investigators recruited 328 hospitalized COVID-19 patients from 2 hospitals in Belgium. All participants were confirmed to have COVID-19 via a PCR test, and 50 of the 283 (18%) required intensive care shortly after hospital admission. In addition to being 18 years or older, study patients could not be involved in any ongoing clinical intervention studies and could not have moved within the last 3 years.

Primary study outcomes were the duration of hospitalization and admission to intensive care. Secondary endpoints included vasopressor usage, need for invasive ventilation, and blood oxygen saturation.

The investigators determined daily exposure levels from 2016-2019 for particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), and black carbon using a high-resolution spatiotemporal model. Blood black carbon particles (internal exposure to nano-sized particles) were determined using pulsed laser illumination.

The participants averaged 65.7 years of age, 52.4% nonsmokers, 85.7% White, and 57.5% male. At 9.8%, patients with north-African ethnicity represented the second largest population. Additionally, 56.6% had congestive heart failure, 22.3% had diabetes, and 19.2% had cancer.

The average hospitalization duration was 16.9 days. The strongest determining demographic predictor of time hospitalized was, unsurprisingly, patient age. When the investigators controlled for all other demographic and clinical variables (including sex, BMI, education, median neighborhood income, smoking status, Charlson comorbidity index, average temperature at admission, date of admission and estimated virus variant), they found that for each 10-year increase in patient age, hospitalization duration increased by 2.36 days.

After controlling for all the above demographic and clinical variables, the results showed that an interquartile range (IQR) increase in exposure the week before admission was associated with an increased hospitalization duration (PM2.5:+4.22 (95%CI:0.74-7.69) days; NO2:+4.33 (1.30-7.37) days.

The investigators found similar outcomes for long-term NO2 and BC exposure. Notably, the effect-sizes for an IQR increase in air pollution on hospitalization duration were comparable to a 10-year increase in age. For an IQR higher blood black carbon load, the odds ratio of needing intensive care hospitalization was 1.36.

Additional results included the finding men averaged 3.99 days longer in the hospital than women. Date of hospital admission was also associated with duration of stay, but the study authors wrote, “None of the other covariates were significantly correlated with the duration of hospitalization.”

The study authors concluded that hospitalized COVID-19 patients with higher pre-admission ambient air pollution and blood black carbon levels had higher adverse outcomes. “Our findings imply that air pollution exposure influences on COVID-19 severity and therefore the burden on medical care systems during the COVID-19 pandemic,” they wrote.

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