Francesca Tomasi received her B.A. from the University of Chicago and currently does microbiology research.
Here on Infective Perspective, we have already discussed disease transmission on airplanes and the effects of our highly interconnected world on the global spread of infections. But have you ever wondered how quickly and widely a pathogen could spread in a metropolitan area?
On Monday, researchers released a harmless, invisible, odorless gas at Grand Central, Times Square, and/or Penn subway stations in New York city. Their goal is to study how exactly air moves through subway tunnels and extrapolate this information for an action plan in the event of a bioterrorism attack in one of the world’s busiest metropolitan areas. Prior to releasing this gas, researchers planted detectors in over 55 different metro stations as well as some other locations in the area. These detectors will pull air through filters and capture particles into bags for analysis.
The tracer gas that was sprayed into the air for this experiment is called perfluorocarbon (chemical formula CxFy). Thousands of detector samples collected over several days will be analyzed for concentrations of perfluorocarbon in order to deduce the gas’s dissemination activity. Preparation of the samples for analysis will require removing any impurities from the collection bags. This is done for instance by adding hydrogen to the sample and introducing a catalyst that converts the hydrogen and any oxygen present into water. After removing the water, the sample is analyzed. This is typically done using gas chromatography, which separates and allows for subsequent analysis of different vaporized compounds. This way, perfulorocarbon particles will be separated from other particles and detected using techniques such as mass spectrometry. This entails bombarding the sample with electrons and measuring how many negative ions are produced. Perfluorocarbons have a high electron affinity and can therefore be detected even in very low concentrations.
Scientists want to know where aerosolized particles tend to settle, and if (or how) they re-disperse when trains zip by. Furthermore, with the frequent opening and shutting of metro doors, particles could flow into the train cars and settle in and on passengers. Of course, we hope never to have to use the data that will eventually come out of this week’s test runs in New York City. Even if a biological contaminant is introduced by accident (i.e. not out of malice but rather from a natural outbreak), New York City’s subway system transports over 5 and a half million people every day and an infection can probably go a long way. Researchers are now taking proactive measures to quantify the extent to which a dangerous biological aerosol can in fact spread in a high-volume metropolitan area. Most of the results will not be made public for obvious reasons. However, it is a good idea to assume that viruses and bacteria can readily spread in an enclosed, busy area like metro trains and stations. For that reason, it is always important to wash your hands regularly. Hand-washing, after all, is one of our best anti-infection tools.