Study sees no evidence of a positive relationship between city-level transit ridership and influenza/pneumonia mortality rates.

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Looking into influenza/pneumonia death rates and transit ridership, a team of New York University researchers has found, in a new study, that local rates of public transportation use are not significantly associated with the prevalence of viral respiratory diseases.

“We find no evidence of a positive relationship between city-level transit ridership and influenza/pneumonia mortality rates,” the study of national data for 121 cities finds. These findings suggest “population-level rates of transit use are not a singularly important factor in the transmission of influenza.”  While the study does not compare individuals who do and do not use public transit, it finds that cities where public transit use is very common do not have systematically higher influenza and pneumonia rates than cities where hardly anyone uses public buses and subways.

Published in the research journal PLOS ONE, the study comes amid high public concern about the role of transit ridership in the spread of COVID-19, though it does not deal directly with coronavirus infection.

Its authors—Renata Howland, Nicholas Cowan, Scarlett Wang, Mitchell Moss and Sherry Glied of NYU Wagner and the NYU Rudin Center for Transportation housed by the graduate school of public service—examined U.S. Centers for Disease Control and Prevention (CDC) data on death rates from influenza and pneumonia from 2006 to 2015.

They also incorporated surveys that measure the proportion of adults who commute for at least an hour daily on public transit, taking advantage of the considerable variation in the use of city-level public transit in American cities.

The data suggest that even in transit-dependent cities like New York, where 57 percent of adults commute on public transport, public transit is not a significant factor in mortality rates where influenza/pneumonia was the underlying cause, a proxy for disease prevalence.

“Scientists believe that COVID-19 spreads in a very similar way to influenza.  To the extent that’s true, this study, consistent with several others that have looked at COVID-19 in other countries, points to the possibility that public transit has not been an important contributor to COVID-19 spread,” said Glied, the dean of NYU Wagner and a health economist.

In the future, further study, the authors note, could illuminate the causes of spread on public transit, along with rider strategies and habits that have protected riders from respiratory illnesses.

“In several of the cities under consideration, over 1 million riders are taken on public transit each day, and riders encounter hundreds of other riders, often in closed, indoor spaces,” they noted in the study. “On the other hand, transit riders generally do not speak to one another and often try to avoid physical contact. More research is needed on the factors that contribute to transmission of viruses in this context.”

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