The tenuous link between the metro and Covid-19

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On April 13, Jeffrey Harris, economist at the Massachusetts Institute of Technology, published an unrevised peer-reviewed study with a provocative title: “The Subways Seeded the Massive Coronavirus Epidemic in New York City”.

In the working paper now available at the National Bureau of Economic Research, Harris maps metro turnstile data to infection rate by zip code, and says the recent flattening of New York’s epidemic curve is linked to the 65% drop in ridership that occurred in the first half of March. In an editorial from New York Daily News detailing the contents of the newspaper, it also highlights the heavy death toll among MTA workers, which hit 79 people on April 20, as other evidence.

The study has been widely rejected. Over the past week, mathematicians, infectious disease researchers and transit policy experts have criticized Harris’ methods, warning that it does not provide statistical evidence and ignores important confounders. That didn’t stop his conclusions from now providing fodder for political debate on social media, conservative radio talk, and among city decision makers on the appropriate public health response to the coronavirus. A Queens politician quoted the newspaper on Sunday as calling on New York Governor Andrew Cuomo to shut down all subway services on Sunday.

In this moment of deep uncertainty for public transit agencies, the dialogue around the document shows how easily metros and buses can be scapegoats, even if they provide millions of essential trips during the pandemic.

To arrive at his deduction, Harris presents a series of thematic maps supposed to map occupied train lines to infection rates, claiming that subway lines are the “right unit of analysis” for studying the role of the system. The map that has been most widely shared online shows some of the stops along the 7 train – the local Flushing line – superimposed on a zip code infection rate map as it travels from Manhattan to the heart of Queens . He also notes the decline in ridership relative to the city’s epidemic curve.

Yet disease modeling experts say the data visualizations that Harris includes do not seem to clearly support the correlation he is trying to draw: for example, only 13 of the 22 stops shown on his map of the local Flushing line are located in postal codes with infection rates greater than 100 per 10,000 people.

Stops along the local Flushing line in the New York subway system, superimposed on a postal code infection rate section, with case data from April 8, 2020. The lightest shade of green indicates the areas with less than 70 cases per 10,000 inhabitants. The next darkest shade indicates the areas with more than 70 but less than 100 cases per 10,000 population. The darkest green indicates areas with more than 100 cases per 10,000 population. Harris writes: “The outside area of ​​each point corresponds to the volume of turnstile entries during the first week of March 2020, while the inside area corresponds to the volume during the third week of this month. (Jeffrey Harris / National Bureau of Economic Research)

The document also does not try to unravel the many confounding factors that could easily make the metro not the main vector. In the absence of statistical analysis to contextualize the importance of the figures it presents, it is impossible to say that ridership is more than a reflection of the other types of activities which decreased in mid-March, after the closure of public schools and restaurants and the maintenance of activity. home orders have been issued.

“The closure of schools, the closure of workplaces and the reduction of contact with the community have resulted in a reduction in transmissions,” said Philip Cooley, member emeritus of the non-profit research organization RTI International, who spent his career studying the transmission of viral diseases through computer biology. “In other words, the reduction in ridership in the metro is an indirect indicator of the increase in social distancing practices, and it is the culmination of all these social distancing practices that have flattened the curve. ‘infection. “

Abbey Collins, director of communications for the New York MTA, called the document “defective – full stop.”

Public transport researchers also warn that no such dramatic link between the use of public transport and viral spread has been found elsewhere in the world. For example, the city with the longest metro network in the world, Seoul, may also be among the best for controlling Covid-19. The fact that the most recent increases in infections are occurring in rural areas of the United States could also give gullible readers a break. Salim Furth, senior researcher in urban economics at George Mason University, dissected the article on the blog Market Urbanism and determined that more attention should be paid to the infectious threat of car travel, considering (among others factors) that Staten Island, New York City’s least dependent public transit district, now has the highest infection rate in the city.

In a dying blog article criticizing the article, mathematician, transit analyst and CityLab contributor Alon Levy detailed several reasons why metro and track workers could have been more severely affected than cyclists – “Contamination at work is not the same as contamination during travel,” writes Levy. .

Harris argues that the basic premise of the argument is sound. “From the point of view of the highest level of evidence, this is a correlational study – there is no way around this,” he said. “On the other hand, I don’t see how a serious public health practitioner, after examining the facts, would have recommended other than focusing heavily on the metro system like the fuse that ignited the epidemic in New York. “

But where the facts point, many infectious disease experts say, it was a few critical days in early March that daily life continued after the virus was established in the city of eight million people. ‘inhabitants, but before the entry into force of public health directives. This mismatch is the main explanation for why New York City ended up at the top of the world in coronavirus cases: long before the subway traffic fell, “the damage was already done,” said Robyn. Gershon, clinical professor of epidemiology at New York University with an emphasis on occupational and environmental health and safety. “The virus was already spreading. “

This is not to say that the germs did not spread in the metro. As one of the many places in New York where people congregate, subway cars have undoubtedly magnified the coronavirus pandemic, said Gershon. But to measure with confidence the role it has played in relation to taxis, schools, restaurants, workplaces and other shared spaces, one would need “an important and costly study with many graduate students.” A researcher would likely need to clean up a large number of subway poles, conduct a detailed investigation of the routes and commuting habits of a representative sample of thousands of cyclists, and pass antibody tests for each. , like what Gershon did in a 2009 analysis of the impact of subway noise on hearing loss among New Yorkers published in the American Journal of Public Health.

Gershon is now preparing for new investigative research: says she hopes to partner with the Transit Workers Union to study how working conditions and working practices could have led to high infection rates and number of Covid-19 deaths among MTA workers.

Alternatively, a scientist could build a simulation of virus transmission and run it over a synthetic population that reflects the actual demographics of commuters over several weeks. This is what Cooley did to study the role of the subway in the transmission of H1N1 in New York in 2009, concluding that 4.4% of citywide infections were transmitted via the subway. If the subway service had been suspended at the time, he said, it could have reduced the total number of infections in New York by 12.5%. Since the coronavirus is much more contagious than H1N1, Cooley speculates that the underground infection rate for Covid-19 would be even higher.

However, the mysteries of the coronavirus would present a major challenge in replicating this type of study, said Cooley. Above all, with H1N1, Cooley knew the rates of immunity to viruses and re-infection among New Yorkers. Because the coronavirus is so new, with no prior human immunity, an uncertain incubation period, and an unknown rate of reinfection, a safe simulation of transmission across New York may not yet be possible.

The Harris newspaper proves at least one thing very clearly: the ease with which the metro can be blamed for an invisible disaster, especially in a very partisan environment that pits cities almost everywhere else. Transit has long carried a social stigma in the self-governing United States, with low-income people of color and other marginalized groups constituting an inordinate share of passengers. New York City was already a national outlier in many ways, including the use of public transit. Now, with the help of the MIT newspaper, his famous metro has become ammunition in the growing war against coronavirus culture. “It is rather strange to see New York journalists losing their shit on the beaches of FL while the New York subway is still operating,” said Kyle Smith, spokesperson for the National review, tweeted saturday. “It seems obvious that the metro was a primary means of spreading the disease, perhaps the most important means across the country. “

In response to board members, the MTA defended its operations as an essential form of transportation for “the doctors, nurses, first responders, grocers and pharmacists, and other personnel essential to get to work and save Lives”.

New York City leaders will soon face the late response to the coronavirus and the mass transit workers who are dying in such large numbers. Before the pandemic, the MTA already had work to do to improve service delays and overcrowded trains, and it is not known how the agency will now move forward, faced with an 8.5 billion deficit dollars and a continued need for strengthened health and sanitation protocols. But in a city as large and densely populated as New York, public transit drives the economy; while some commuters with means can choose to buy cars when the lock is released, many workers and students will inevitably get back on track. Said Gershon: “We can never reopen without the metro. “



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