These are your chances of catching COVID-19 on a train

Photo: Diego Torres Silvestre via Flickr

As we enter August and the dog days of summer, everyone is feeling reminiscent of simpler summers past. Sun-soaked vacations and getaways that were once easily within reach now feel like fairytales and pipe dreams thanks to COVID-19. While train stations are still operating, millions of Americans are wary of boarding such vehicles due to the risk of catching coronavirus.

But, just how likely are you to catch COVID-19 on a train? A team of researchers from the University of South Hampton set out to find out. Using Chinese train route and passenger information in combination with subsequent passenger COVID-19 infection rates, the team at USH came to several conclusions.

To start, while the chances of catching the coronavirus on a train are undoubtedly higher than they would be in a more open space, one’s odds largely depend on just how close they are sitting to an infected coronavirus carrier and the amount of time they stay on the train in general.

“Our study shows that although there is an increased risk of COVID-19 transmission on trains, a person’s seat location and travel time in relation to an infectious person can make a big difference as to whether it is passed on. The findings suggest that during the COVID-19 epidemic it is important to reduce the density of passengers and promote personal hygiene measures, the use of face coverings and possibly carry-out temperature checks before boarding,” explains lead investigator Dr. Shengjie Lai in a release.

Moving along to more exact specifics, statistics, and percentages, researchers noted that up to 10.3% of passengers sitting within three seat rows (horizontally) and five-seat columns (vertically) from a coronavirus positive person (index patient) ended up catching COVID-19 themselves in some scenarios. All in all, the average rate of transmission for people coming into “close contact” with infected individuals on a train was calculated to be 0.32%.

This project was an undertaking of WorldPop, a human population mapping initiative at the University of South Hampton. In collaboration with numerous Chinese entities (the Chinese CDC, the Chinese Academy of Sciences, etc), the USH WorldPop researchers used a complex model to analyze both trip and infection rate data among train passengers riding China’s high-speed train networks. Essential to this process was the identification of train passengers who were either COVID-19 positive themselves or had come into close contact with an infected person within 14 days. These passengers were considered the “index patients.”

In total, this analysis encompassed trains running between December 19th, 2019, and March 6th, 2020 carrying 2,334 index patients who came into close contact with 72,093 other people. Passengers’ travel times varied between less than one hour to as long as an eight-hour trip.

Where is the absolute worst spot to be on a train during a pandemic? Predictably, the study’s authors say passengers sitting directly beside a coronavirus-carrying individual showed the highest rates of infection. On average, 3.5% of people sitting right next to an index patient contracted coronavirus, and 1.5% of people sitting in the same row as a COVID-19 carrier tested positive later on.

The “attack rate” of each seat on a train was also calculated. Researchers came to this estimate by first determining how many COVID-19 diagnosed individuals sat in a specific chair during the analyzed period. Then, that number was divided by the total number of all passengers who had used that seat. Generally speaking, this process led to the conclusion that a train seat’s attack rate increased by 0.015% every hour someone sitting in that seat was located close to an index patient. If an index patient happened to sit right next to the seat in question, the attack rate would jump by 1.3% every hour.

Surprisingly, however, it was also agreed upon that only 0.075% of people who sat in a seat directly after an index patient actually contracted the coronavirus.

In conclusion, the research team says a distance of 3.3 feet is adequate to stay safe when sitting in the same row as an index patient for an hour-long train trip. However, in the event of long train rides (two hours +), at least an eight-foot distance is advisable.

“Our research is the first to quantify the individual risk of COVID-19 transmission on public transport based on data from epidemiological investigations of disease cases and their close contacts on high-speed trains,” professor Andy Tatem, director of WorldPop, concludes. “It shows that the transmission risk not only relates to the distance from an infected person but also the time in their presence. We hope it can help to inform authorities globally about measures needed to guard against the virus and in-turn help to reduce its spread.”

The full study can be found here, published in Clinical Infectious Diseases.