“I think it’s fair to say that in general, the flu and colds and other things are spread person to person,” Morse told me. “There’s no question that the more contact you have with people, the greater likelihood you are exposing yourself to infection. If you are a hermit and presumably have no contact with people, you are at very low risk.”
As with so many things in my past, leaving my house, in general, is probably where I went wrong. Before we get too finger-pointy at the subway, though, Morse cautions not to assume causation where mere correlation might be at hand. The main risk factor for contagion is proximity to other potentially sick people, no matter whether those people are on the train, in your office, or standing in line to get a lunchtime chopped salad just like you. So all those smiling faces, welcoming me to my new job with a firm handshake? One of them could have very easily been patient zero for my clogged sinuses, and how I got from my apartment to their cubicle or conference room wouldn’t have mattered at all. Cold and flu season is other people.
And in temperate regions like the northeastern United States, it really is a season—tropical and subtropical areas don’t experience the winter-specific cold and flu explosion that places with cold winter weather typically have, according to a 2016 study. So my big mistake might not have been getting on public transit or meeting my new coworkers, but instead, doing all that in the first chilly month of the year in New York. There have long been theories about why cold weather is a breeding ground for rhinovirus. It could be because you socialize more in close quarters when it’s cold out. A 2017 study from researchers at Yale University suggests the decreased temperature itself could be to blame. The study was conducted on mice, but it found that even a 7-degree dip in temperature was enough to suppress their natural immune response to infection.
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If you’re feeling immunologically smug because you’ve been riding public transit to work every day for years and assume that’s built up your general resistance to illness, I hate to burst your bubble, but you have the same likelihood of coming down with the sniffles on any given day as anyone else who ventures along a similar path. People in this situation might be conflating their supposed resistance to the common cold with the hygiene hypothesis, according to Morse, which is the idea that allergic and autoimmune reactions are made worse when people are kept away from irritants, depriving their immune systems of the chance to build up a response. “The evidence on that is mixed,” Morse says. “And with colds and viruses, there are so many of them. If you ride the subway often, you’re likely to be exposed to more of them, and you may be getting colds more often.”