Higher long-term exposure to pollutants PM2.5 (ie, particulate matter <2.5 µm in diameter), PM10 (ie, particulate matter <10 µm in diameter), and NO2 (nitrogen dioxide) increased the likelihood of developing COVID-19–associated pneumonia in patients with multiple sclerosis (MS). These are the findings of a study published in Multiple Sclerosis and Related Disorders.

Recognizing that pneumonia is the most common complication among patients with severe COVID-19, researchers sought to evaluate the effect of long-term exposure to PM2.5, PM10, and NO2 on the severity of COVID-19 among individuals with MS. They designed a 1:2 ratio case-control study of patients with MS who were living in Italy and became infected with COVID-19, differentiating those with severe COVID-19 from control individuals according to the occurrence of documented pneumonia.

Among a total of 615 eligible patients, 491 provided a detailed place of exposure and thus were included in the principal analysis. In the remaining 124 individuals, the zip code of their referred MS center was used as a proxy for the exposure and they were included in the sensitivity analysis only. Median age was 46 years (Interquartile Range =36-55), but patients with MS with pneumonia were significantly older than those without pneumonia (P <.001).

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The researchers found that pneumonia was reported as a complication of COVID-19 in 169 of the participants. Average exposures to pollutant concentrations were higher among patients with pneumonia compared with individuals without pneumonia (PM2.5: P =.020; PM10: P =.092; NO2: P =.009).

Higher levels of air pollutants were associated with increased odds of the development of COVID-19 pneumonia:

  • PM2.5: third vs first tercile [odds ratio {OR}, 2.26; 95% CI, 1.29-3.96]
  • PM10: third vs first tercile [OR, 2.12; 95% CI, 1.22-3.68]
  • NO2: third vs first tercile [OR, 2.12; 95% CI, 1.29-3.69]

The pollutants highly correlated with each other. The weighted quantile sum (WQS) index was associated with a significantly increased risk for pneumonia (P =.004), with key contributors to this association being NO2 (41%) and PM2.5 (34%). Consistently, the Least Absolute Shrinkage and Selection Operator (LASSO) penalized regression method chose PM2.5 and NO2 as the most dangerous pollutants.  

Several study limitations should be noted. To begin, future research that evaluates other additional pollutants (besides PM2.5, PM10, and NO2) within the environmental mixture should help to guarantee a more complex overview. Another study limitation is related to the exposure assessment. In particular, since some individuals with MS are quite active, it is thus not unlikely that they have long-distance commutes to work. These individuals may find it difficult to decide on where they spend most of their active time — that is, at home or at their place or work. With such indecision, participants might report only one place of exposure, thus introducing a possible source of bias.

The researchers concluded that “… [E]ven if several other factors may explain the unfavorable course of Covid-19 infection, also air pollution plays its role and since it is a modifiable exposure, urgent measures should be adopted especially to protect the most vulnerable population.”

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures. 


Ponzano M, Schiavetti I, Bergamaschi R, et al; MuSC-19 Study Group. The impact of PM2.5, PM10 and NO2 on Covid-19 severity in a sample of patients with multiple sclerosis: a case-control studyMult Scler Relat Disord. 2022;68:104243. doi:10.1016/j.msard.2022.104243

This article originally appeared on Neurology Advisor