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‘Don’t worry. I’m no longer contagious.’ Yeah, right

A microbiologist cautions that people often are wrong about how they got infected and deluded about whether or not they themselves are still infectious.

'Don't worry. I'm no longer contagious.' Yeah, right
As we rarely get a positive identification of the microbes that inflict us, making assumptions about our own levels of contagiousness is not such a good idea.

Microbiologist Jenny Rohn made some great points last week in an article in the Guardian about the “microbiological delusions” that people have about common infectious diseases, such as colds, flu and viral gastroenteritis.

By far, the most delusional of these beliefs is the one offered frequently by sneezing, coughing, runny-nosed people when they see others backing away from them: “Don’t worry. I’m not contagious.”

As Rohn points out, that may be true. But it also may not be true. And just because you think it’s true, doesn’t make it so.

Here’s why, writes Rohn (with British spellings):

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Quite understandably, once our symptoms have peaked and we’re feeling a bit better, we may assume that the danger of spreading illness is past. But is it really that simple? It all depends on the particular microbe and strain. Rhinovirus, for example, one of the agents that causes the common cold, loads up your snot with so many particles that you can easily be infectious a full two days after your symptoms hit, and possibly longer. Other bugs have different windows of contagion, and even considering the same agent, strains can exist with more behavioural diversity.

As we rarely get a positive identification of the microbes that inflict us, making assumptions about our own levels of contagiousness is not such a good idea.

And then there’s that whole blaming thing — the infected person’s belief that they know exactly who gave it to them (you, for instance).

Here’s Rohn on that touchy topic:

There are untold numbers of contagious microbe strains on the prowl, each with their own incredibly complex infection processes. Because of the variability of incubation periods and viral shedding windows (which can range for days), the most obvious culprit — your spouse, your child at nursery, the chap who sneezed all over you on the Victoria line — may be a red herring. …

On an average commute to work on London Underground, for example, you might come closer than you’d ideally like to hundreds of people in the carriages and tunnels and platforms; that handrail or escalator rail you are clutching could have been sweated on by thousands before you, many of whom have probably wiped their runny noses with a stray hand.

Unless you are confined at home with no regular visitors, pinpointing the exact moment of infection would be impossible; determining if your strain is the same as your work colleague’s would require complex sequencing procedures well beyond your pay grade.

Rohn also calls people to task for professing to know how long someone else’s cold or flu will last because, after all, they’ve just gotten over the same thing.

Once again, it may not be the same virus. And even if it is the same one, says Rohn, “differences in our own genetic backgrounds, overall constitutions and previous exposure-based immunities can make the course of the same disease quite different in two different individuals.”

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So, the next time you (or someone you know) comes down with a nasty cold or flu bug, don’t start making assumptions about who gave it to you or when you’ll no longer be infectious.

But do try to keep those delusions — and your infection — to yourself.

You can read Rohn’s article on the Guardian’s website.