According to investigations at the centre's Institute of Environmental Diagnostics and Water Research (IDAEA) and the Blanes Centre for Advanced Research (CEAB), air-quality examinations at the peak of the last major influenza outbreak showed the underground train network in Spain's second-largest city was one of the safest places to be.
A total of 10,000 bacteria per cubic metre of air live in the complete metro system in Barcelona, the majority of which are harmless to humans.
And this figure is far lower than the amount of airborne bacteria found in airports – or in GP surgeries and walk-in clinics, the CSIC reveals.
Their research forms part of the European Improve Life project, which evaluates air quality in public areas and proposes measures for improvement, but little is needed in the bowels of Barcelona as only 2% of bacteria found has any potential to cause illness in humans, including the common cold.
This shows, says Xavier Triadó of the CEAB, that passengers themselves are not a major source of 'biological risk'.
The team checked air quality inside carriages on the metro as well as in the stations, stairwells and entrance areas where ticket booths are located, between November 2013 and February 2014, when a national 'flu epidemic had reached its peak.
CSIC researchers say this is only a pilot study, which is replicable in times of zero epidemic and which should be continued over time to examine fluctuations in bacteria quantity year-round.
Among the 2% of harmful bacteria were the A and B strains of the influenza virus, a rhinovirus – which causes nose and sinus inflammation and hayfever – and a type of fungus known as Aspergillus Fumigatus.
“We spend 90% of our lives in enclosed spaces nowadays, and the air within them can be a channel for transmitting certain pathogens,” Triadó explains.
“That's why monitoring the quality of the air – a feature of underground train travel which does not get much attention, despite the high volume of people present at any one time – is so important.”
Underground air can also contain pollutants from traffic, via ventilation systems open to the roads above and from the entrance to the metro, the CSIC explains.
The study is a useful tool in predicting viral epidemics, given that 100 million people a day use underground train systems in some 200 cities worldwide and, in Barcelona, the metro accounts for 50% of daily travel around the metropolitan area, transporting 1.25 million people every working day.
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