One of my favorite benefits of going to Washington University in St. Louis is receiving a complimentary U-Pass that allows me to travel throughout St. Louis. However, when I invited a friend to ride with me, they expressed concern about taking public transit during the height of a pandemic. It made logical sense: multiple individuals from across the city touching the same handles and seats would likely spread an illness to the next unlucky passenger.
Although the pandemic is slowly burning out, ridership on public transportation has likewise made a return throughout the United States . As more and more people are making their way onto trains, busses and subways, could I be stepping onto a human petri dish that is spreading the next outbreak, epidemic or even pandemic?
Obviously, this concern is not a new one prompted by COVID. Epidemiologists and public health experts have paid particular attention to pathogens spread by public transit, such as the bacterial genus Staphylococcus (Staph). Staph thrives on human skin and can therefore spread on high-touch surfaces. Additionally, it is well known for having multiple antibiotic resistant strains. This can have profound effects on individuals with bacterial infections since antibiotic resistant infections cost America 4.6 billion dollars in 2017, with Methicillin Resistant Staphylococcus aureus (MRSA) and ESBL-producing bacteria (such as Escherichia coli) making up the majority of the cases and the cost . Thus, if public transit serves as a reservoir for antibiotic resistant bacteria, it could potentially infect riders and negatively affect their health.
One study looking into Staph on public transport focused on the subway system in Shanghai, China. Shanghai is home to an extensive subway system with 480 miles of track and 6.88 billion riders in 2019 . In contrast, the St. Louis Metrolink only has 46 miles of track and had 13 million riders that same year . Researchers from Fudan University in Shanghai demonstrated that Staphylococcus aureus found on the metro were resistant to 2.64 different antibiotics on average, similar to the number for those in hospitals (2.94) . Additionally, 90% of Staph samples were resistant to at least one antibiotic . Worryingly, metro samples also formed more biofilms compared to hospital samples (22% versus 15% respectively) , meaning that they could better withstand disinfectants and transmit antibiotic resistance genes more easily.
This finding is significant because hospitals tend to contain large numbers of antibiotic-resistant bacteria due to the heavy usage of antibiotics within the facility. Thus, it is concerning that the metro shares a similar incidence of antibiotic resistance as a center of transportation for a large population. However, the Shanghai metro system is far larger than most metro systems in the United States. Thus, it is important to look at a study conducted in America to better understand the risk that public transportation poses at home.
Luckily, there has been research into Staphylococcus in Portland, Oregon. This city is home to TriMet’s MAX light rail. In 2011, MAX carried 34 million passengers in 2011 and consisted of 60 miles of track . In a 2011 study of Staphylococcus on TriMet, the authors found that around 45% of samples were resistant to penicillin and ampicillin antibiotics and were primarily found on felt seats and floors. This is considerably lower than the number from Shanghai, likely due to the lower ridership and smaller extent of the transit system, providing fewer opportunities for riders to contact or transmit resistant strains.
Although many studies looked at Staph on public transit systems, the bacteria is unlikely to cause an epidemic or pandemic. Rather, the most recent pandemics have primarily been due to viruses such as SARS CoV-2, MERS, Ebola and H1N1. This is because bacteria generally have “slower speed of replication and accumulation of mutations” relative to viruses . Moreover, antibiotic-resistant bacteria are “unable to efficiently infect human hosts that are not compromised or hospitalized” . Thus, antibacterial-resistant Staph may complicate individual infections but often fail in spreading through, and causing illness in, a large population. Unfortunately, compared to studies on Staphylococcus, there are far fewer studies looking at the spread of viruses on public transit. Therefore, we need to prioritize research into the subject if we are concerned about the spread of epidemics and pandemics.
Of the few studies on public transport’s spread of viruses, one is of the London Underground in the United Kingdom. The authors of the UK study found a correlation between Influenza Like Illnesses (ILI) and transit stations, demonstrating that areas where riders would need to transfer between lines more often were more likely to develop ILIs . Therefore, it appears that there is correlational data supporting the notion that public transportation may spread illnesses such as the flu between individuals in a city.
However, researchers from New York University criticize the UK study, saying that it “included only one year of data and did not directly measure the share of people in each borough who ride the underground” . Therefore, the study would have counted individuals who biked or walked and still got sick as Underground riders, calling the correlation into question. In contrast, the New York University researchers found no correlation between increasing/decreasing public transit ridership and influenza/pneumonia deaths . Their study is one of the most rigorous studies investigating public transportation’s spread of viral respiratory illnesses. Not only does it examine nine years worth of data, but it does so for 120 major cities in the United States (including St. Louis). Furthermore, they controlled for confounding factors such as income and population density . Therefore, it is highly probable that American local public transit alone does not contribute to the spread of viral respiratory illnesses such as the flu or pneumonia.
Although the researchers could provide no explanation as to why public transportation might not transmit respiratory viral illnesses, the finding is still valid for the metro system here in St. Louis. Thus, the metro system does not necessarily pose a significant risk to public health beyond occasional limited infections in individuals.
One might object, pointing out that if public transit itself doesn’t spread viral diseases, then why did COVID-19 rise to epidemic proportions in China during the Chinese New Year when workers took trains home to visit family? A quick look at this question will also reveal the answer. As opposed to local public transportation examined above, the implicated railways travelled between major cities instead of within them. Furthermore, the utilization of inter-city rail is more extensive in China than in most other nations . Therefore, there are more people on trains travelling between multiple large cities, providing a larger number of individuals from a diverse geographic area to spread a novel viral disease. In contrast, systems such as the St. Louis Metro travel primarily within the St. Louis area. Thus, they do not carry large numbers of individuals from across the country, reducing the risk of someone boarding and then spreading a disease nationwide, resulting in an epidemic or pandemic.
Therefore, should we be concerned that we might catch some transmissible disease while riding the metro? Probably not. However, the possibility of catching some illness, such as an antibiotic resistant infection, is not excluded, particularly if you are immunocompromised or will be undergoing surgery. Thus, common sense will likely be useful in reducing the risk of individual infection, such as washing hands and wearing a mask. Furthermore, metro systems need to ensure that surfaces remain clean and sanitized, particularly surfaces that see the largest bacterial load. In doing so, we might not be preventing a global pandemic but we will certainly be providing a safer and cleaner environment for riders and our community.
Edited by: Katherine Shao