While long suspected, the role of public transportation in the spread of influenza-like illness has not been proven until now.

Research published in Environmental Health focused on the London underground and found higher rates of airborne infection in Londoners that have longer tube journeys through busier terminals.

Passengers waiting for the subway. Source: Getty

“The transmission of infectious diseases is dependent on the amount and nature of contacts between infectious and healthy individuals. Confined and crowded environments that people visit in their day-to-day life (such as town squares, business districts, transport hubs, etc) can act as hot-spots for spreading disease,” wrote the study team from University College London and University College Bristol, both in the UK. “In this study we explore the link between the use of public transport and the spread of airborne infections in urban environments.”

Part of what prompted the study was the lack of specific information on disease transmission in public spaces. The authors pointed out that, when the UK Department of Health created the 2011 UK Influenza Pandemic Preparedness Strategy, it found too little evidence that restrictions on mass gatherings will have any significant effect on influenza virus transmission.

“As a consequence, the UK Government’s position on large public gatherings, crowded events travelling and public transport use is not only neutral in light of lack of evidences, but those types of events are even encouraged because they represent an important indicator of ’normality’ and may help maintain public morale during a pandemic,” the study noted.

To try to remedy the dearth of information on the spread of influenza-like illness (ILI) where people gather, the study team analyzed a large number of journeys on the often-crowded. Using publicly data on the electronic tickets used for public transport in Greater London, researchers were able to infer passengers’ routes on the underground network. To estimate the spread of a generic airborne disease in each station, they used and extended an analytical microscopic model that was initially designed to study people moving in a corridor.

‘Comparing our results with influenza-like illnesses (ILI) data collected by Public Health England (PHE) in London boroughs, shows a correlation between the use of public transport and the spread of ILI,” the authors wrote. “Specifically, we show that passengers departing from boroughs with higher ILI rates have higher number of contacts when travelling on the underground. Moreover, by comparing our results with other demographic key factors, we are able to discuss the role that the Underground plays in the spread of airborne infections in the English capital.”

“Our study suggests a link between public transport use and infectious diseases transmission and encourages further research into that area,” the study concluded. “Results could be used to inform the development of non-pharmacological interventions that can act on preventing instead of curing infections and are, potentially, more cost-effective.”