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| Credit CDC PHIL |
#13,741
The ways that influenza can be transmitted have been pretty well described (direct contact, airborne large-droplets, airborne small aerosols & fomites), but the relative risks of becoming infected by each mode undoubtedly varies by environments and scenarios.
What is generally accepted, however, is the more people you cram into a confined space (bus, train, plane, classroom, etc.), the higher the risks of transmission.During a pandemic, the use of non-pharmaceutical interventions (NPIs) - such as school closures or social distancing - will be critical to help limit transmission (see Community Pandemic Mitigation's Primary Goal : Flattening The Curve).
In the past we've looked at some of the assumed higher risk settings for flu transmission, including:
Study: Simulated Influenza A Transmission In An Office Environment
Hong Kong Closes Schools, Calls For Stringent NPIs To Combat Flu
ICAAC Video: How Quickly A Virus Can Spread In A BuildingIn 2008, we looked at Japan's testing of Social Distancing On Commuter Trains during a severe pandemic, and in 2011's Viruses With A Ticket To Ride, we looked at a study that appeared in BMC Infectious Diseases, that looked at the incidence of ARI (Acute Respiratory Infection) presenting within 5 days of train or tram travel in the UK.
BMJ: Flu Transmission Risks On Airplanes
They found that recent bus or tram use within five days of symptom onset was associated with an almost six-fold increased risk of consulting for ARI.All of which brings us to a new research article, published in Environmental Health, that - using some pretty heavy statistical analysis that are well above my pay grade - suggests a link between travel on the London Underground and the spread of respiratory infections.
Analysing the link between public transport use and airborne transmission: mobility and contagion in the London underground
Lara Goscé Email author and Anders Johansson
Environmental Health201817:84
https://doi.org/10.1186/s12940-018-0427-5
© The Author(s) 2018
Abstract(Continue . . . )
Background
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. In this study we explore the link between the use of public transport and the spread of airborne infections in urban environments.
Methods
We study a large number of journeys on the London Underground, which is known to be particularly crowded at certain times. We use publically available Oyster card data (the electronic ticket used for public transport in Greater London), to infer passengers’ routes on the underground network. In order to estimate the spread of a generic airborne disease in each station, we use and extend an analytical microscopic model that was initially designed to study people moving in a corridor.
Results
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. 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.
Conclusions
Our study suggests a link between public transport use and infectious diseases transmission and encourages further research into that area. 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.
The University of Bristol has provided an accompanying press release:
Public Release:Tube travel linked to the spread of flu-like illnesses
Despite the commuter cold being a widely accepted concept, it has never been proven that public transport contributes to the spread of airborne infections. Now new research on the London underground commute has proven a link does exist.
The study, published on December 4, 2018 in Environmental Health, will help to inform measures to control the spread of infectious disease.
By comparing Oyster card route information and Public Health England data on flu-like illnesses, Dr Lara Goscé from the University of Bristol's Department of Civil Engineering and Dr Anders Johansson from Bristol's Department of Engineering Mathematics, discovered higher rates of airborne infections in Londoners that have longer tube journeys through busier terminals.
Dr Goscé explained: "Higher rates [of influenza-like cases] can be observed in boroughs served by a small number of underground lines: passengers starting their journey in these boroughs usually have to change lines once or more in crowded junctions such as King's Cross in order to reach their final destination.
"On the other hand, lower influenza-like rates are found in boroughs where either the population do not use public transport as the main form of transport to commute to work; or boroughs served by more underground lines, which guarantee faster trips with less stops and contacts with fewer people."
For instance, one finding highlighted that infection rates in residents of Islington, who often change lines at crowded Kings Cross St. Pancreas, were nearly three times higher than in commuters from Kensington, who mostly take direct trains.
The team hopes that their findings will inform Government epidemic policies. Dr Goscé said: "Policy makers, in particular, should address the role potentially played by public transport and crowded events and avoid encouraging the attendance of such environments during epidemics."
Looking to the future, the group want to draw a clearer map of the spread of cold-like infections in a metropolitan environment, and so plan to combine individual level infection data with existing studies from households and schools.
Dr Goscé said: "These results are preliminary following limitations of the dataset. Empirical studies. Empirical studies combining aero-biology and pedestrian modelling would be important in improving model fidelity and devising non-pharmaceutical control strategies tackling threshold densities to minimise numbers of infections and optimal ventilation in different crowded environments."
While I know some people who believe they'll simply hunker down at home during a pandemic in order to avoid exposure, it's neither practical or desirable to simply shut everything down and try to wait out what could be a year (or longer) event.
Very few are equipped to do so, and besides, someone has to keep the lights on, deliver the food, refine the fuel, police the streets, take care of the sick and injured . . . and do the thousands of other things that hold society together.Like it or not, we'll have to find ways to live and work as safely as possible during a pandemic. Else infection with the virus could quickly become the least of our problems.
