The London Underground (also known simply as the Underground, or by its nickname the Tube) covers all of Greater London and some outlying areas. The first part opened in 1863, proving a rich and varied history, and today it consist of 11 lines and carries 1.34 billion passengers per year. A study produced in 2016 showed the London underground network to be relatively efficient compared with other networks, such as the New York subway.
Due to the different lines and their varied, and often criss-crossing routes, there is competition between them over efficiency and other factors, and commuters tend to have their favorite lines. This makes surveys like ‘which is the dirtiest line?’ all the more interesting.
The new survey looks at levels of bacteria and it has been conducted by one of the online medical information sites (it this case online doctor Dr Edd.) The survey reveals the Northern line to be the tube line with the most bacteria, almost three times more the second placed line – Central line.
For the research, volunteers swabbed 60 surfaces on the ten busiest tube lines. Bacterial numbers were assessed by measuring colony-forming units (CFU), expressed as the number of organisms per 10 square centimeters. Being a culture-based method, the testing only related to those bacteria that could be grown on a particular culture medium under a set of defined incubation conditions across a set period of time. It should also be noted that swabs tend to have poor recoveries from surfaces, picking up only around 20 percent of the organisms likely to be present. Despite this significant limitation in terms of accuracy, the results from the different lines are, to a degree, comparable.
The results showed the Northern Line trains to typically harbor 1,600 bacteria for each sample (colony forming units per square centimeter). In contrast, the lowest scoring line, the Hammersmith & City Line, recorded just 18 bacteria per unit of measurement. The station recording the highest bacterial numbers was Stratford, which interestingly is not, by some distance, the busiest station on the network.
There are lots of graphics and analysis on the Dr Edd website. What is missing is any identification results. This prevents any assessment of whether the recovered organisms are pathogenic or pose any risk to human health. High numbers of innocuous bacteria are not a health risk, whereas a few numbers of a pathogen (such as certain strains of Escherichia coli, a potential fecal-oral risk), are.
This leads to some misleading comments on social media, like:
Booniss Everdrunk (@bookiesnacksize) “Brb going to buy a hazmat suit for commuting.”
Alice (@Alicechadfield) “Oh look the @northernline gives us MORE reasons to hate it.”
The survey of the dirtiest Tube lines is not the first of its kind to be revealed this year. A few months ago Digital Journal profiled the figures released by British Transport Police show the areas on the London Underground which are worst for crime. At the top was the Central Line (the red colored line on the underground map). The Northern Line was placed at number four.
