Presented by Stockholm University

Ever wondered how dirty the Stockholm tube is?

Ever wondered how dirty the Stockholm tube is?
Melker Dahlstrand/
Researchers at Stockholm University are ready to get down and dirty on the local metro.

Germs. We know they’re everywhere – but how often do you really think about it?

Greater Stockholm is home to more than 2 million people – and an awful lot of them take the metro each day.

So what are you exposing yourself to when you let your hand graze the rail of the escalator, or when you grasp the bar on the ceiling in panic to avoid smashing the steely-eyed stranger beside you on the evening commute?

Researchers at Stockholm University are determined to find out.

“We want to understand the composition of microorganisms in the underground environment,” says Klas Udekwu at the Department of Molecular Biosciences at the Wenner-Gren Institute of Stockholm University.

 “With further knowledge we can hopefully help to reduce the spread of pathogens.”

Udekwu coordinates the Swedish part of the project together with his colleague Per Ljungdahl – but this project isn’t just about Stockholm. In fact, 46 cities around the world, including New York, São Paolo and Shanghai, are part of the research project, called MetaSUB.

“The environment in the underground is very special,” Udekwu says. “It consists of man-made caves with high air supply and a large flux of people. In many cities, the underground is the main way of transportation. That is why we begin our study there.”

Udekwu and his assistants are collecting samples using nylon buds that they rub against various surfaces in the underground for at least three minutes. DNA is extracted so that researchers can identify the microorganisms and their content of specific genes such as antibiotic resistance.

The first swabbing begins in mid-March, but samples will be collected periodically from all underground stations in Stockholm during the five-year long project. Extraction and analysis are done at Stockholm University, which will also help analyse samples from other cities.

“There are many questions that interest us,” Udekwu says. “We examine, for example, how the environment and the microbe colonies change with weather, seasons and the flow of people.”

By combining the data with information on the urban environment, he adds, it will be possible to examine whether the composition of microorganisms varies depending on access and proximity to hospitals. And that could contribute to better community planning.

“With the help of modern methods we can now, at a molecular level, begin to understand the dynamics of organisms in the cities,” he explains. “Increased knowledge can have a positive impact on sustainability, security and future planning. This includes the basis for the ‘smart cities’ of the future, cities that can detect and react to levels of pathogens.”

But don’t tear your hair out worrying about all those pathogens. While the researchers note that microorganisms have evolved and learned to live among us humans, most of them actually aren’t that harmful. In New York, the first city studied in MetaSUB, researchers found that the majority of metro-riding microorganisms don’t cause disease – and in fact, some of them even help break down toxins.

So climb aboard – but if you see someone intently swabbing the seat next to you, at least you know why. 

This article was produced by The Local and sponsored by Stockholm University.

Images: Stockholm University