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  • Alex Cloherty

The season of Streptococcus

The year was 2010. I was in Scotland with the 'Coast String Fiddlers', the traditional Scottish music band that I was a member of for most of my teenage years. I was absolutely having the time of my life, parading about Edinburgh and Aberdeen with my friends, sneaking my first sip (or two) of Scotch whiskey, and playing my heart out on my bass guitar… until I started to get a very sore throat.

I toughed it out, but as time went on, I distinctly remember wondering, why the heck is this sore throat just getting worse? After a few days, I eventually got to a doctor’s cabinet, where my throat was swabbed and I was promptly diagnosed with ‘strep throat’.

That was, in my memory, my first brush with Streptococcus pyogenes.

Streptococcus pyogenes (which you might also see referred to as ‘Group A Streptococcus’ or just 'Strep A') is a bacterium that exclusively infects humans - and it does a very good job indeed at infecting us, its host of choice. As well as causing strep throat, Streptococcus pyogenes can also cause much scarier diseases, such as necrotizing fasciitis (commonly known as flesh-eating disease), streptococcal toxic shock syndrome or ‘STSS’, and a disease that we are seeing a whole lot of this year: the childhood disease known as scarlet fever.

So, let's fast forward from 2010 to 2022 in the UK. This year, the UK national health security agency recently reported a dramatic upsurge of scarlet fever and other Streptococcus pyogenes infections - with more than double the amount of scarlet fever cases in the autumn of 2022 as compared to that of 2017. And on December 8th, the World Health Organization reported that several other EU member states were also struggling with an increased number of Streptococcus pyogenes infections.

If you’re a regular reader of Microbial Mondays, at this point you might think, ‘Wait a minute. Haven’t I read that paragraph before?’

Well, you’d be pretty spot on. A few weeks ago, I wrote an article about the unseasonable upsurge of respiratory syncytial virus (RSV) infections across much of the world, and I used some pretty similar language. So, why is the same thing happening with this bacterium, Streptococcus pyogenes, as with a completely unrelated virus?

Well, despite the fact that one of these childhood diseases is caused by a virus, and the other by bacteria, some similar forces may be at play.

One possible explanation could be that new, more infectious types of both RSV and Streptococcus pyogenes have evolved over the last few years. Just like RSV, Streptococcus pyogenes can mutate from season to season. Indeed, this bacterium is notorious for ‘changing its winter coat’. In the same way that you might buy a new coat for the new season if your old one is looking a bit drab and you don’t want people to see you looking scruffy, Streptococcus pyogenes is very skilled at pulling a switcheroo with its outer ‘clothing’. And, just like your neighbours might not recognize you when you first go out wearing your new duds, our immune systems cannot as easily recognize Streptococcus pyogenes when it changes its winter coat. That means that our immune systems won’t recognize the bacteria as a danger as quickly as they would if it had still been wearing last year’s winter coat. So, a new winter coat for the bacterium, which can help it sneak under the radar of our immune systems, is one possible explanation for an increase in Streptococcus pyogenes cases.

Another possible explanation is that after the roller coaster of the last two years, our immune systems are not working as well as they used to. One theory to this effect is that of so-called ‘immunity debt’, which is a catchy name for the hypothesis that ‘non-pharmaceutical interventions’ to control COVID-19 (such as social distancing and working from home) accidentally caused a decrease in immunity to a variety of microbes. I covered what immunity debt means more fully in this blog about RSV from a few weeks back. A related theory, which is also underlined by ineffective immune systems, is ‘immunity theft’, or the idea that COVID-19 infection(s) have impaired the functioning of peoples’ immune systems, which puts them at risk for other infections.” I wrote about immunity theft more extensively here.

The thing is, we don’t know yet which of these possible explanations is true - or if a mix of several things are happening at the same time (which I personally think is the most likely). But, regardless of what is causing the increased amount of scarlet fever cases, the actions that you can take to protect yourself and others are the same:

  1. Wash your hands, and sneeze into your elbow. The top ways that Streptococcus pyogenes is spread is via either ‘respiratory droplets’ (sneeze juice), or via direct contact - i.e. your snot gets on your palm and then you pass it to your colleague when you shake hands and voila, the bacterium has a new human available to infect.

  2. If you notice the symptoms of scarlet fever or another Streptococcus pyogenes infection (e.g. a high fever and swollen neck glands), go to your doctor. Streptococcus pyogenes is very easily treatable with antibiotics - so seek treatment if you get it!

Now, I’m not a medical doctor, and there is more detailed advice available here or here (or from your own medical doctor), but judging from what I have read, those two points are the most important take-home messages regarding the high amount of Streptococcus pyogenes infections that we are seeing. Namely, that regardless of why it’s happening, we can prevent it, and we can treat it.

If you’re still stuck on the ‘why’, I get it. I’m curious, too. But, we simply have to wait. Science can move pretty fast sometimes, but it never moves at lightning speed. We simply don’t have enough data yet to know if mutating microbes or languishing immune systems, or all of the above, underlie the increased number of seasonal infections that we’re seeing this winter. But, I can promise you that when we know more, there will be a Microbial Mondays article on the topic.


In the meantime, thank you to my friend Alex for requesting this topic, and for sending me some information that I used to write it (including this page, on which he was interviewed about the steep increase in Strep A cases).

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1 Comment

Dec 23, 2022

Hi Alex, as a doting adult who accompanied you to Aberdeen and the music festival in 2010, I kept waiting for you to comment about the protective efficacy of the single malt whisky you disclosed you (and R****, assuredly) were sneaking on the side. I imagine lower transmission rates in Scotland would be an important clue to follow though I’ll bet that has been thoroughly researched! thanks for the column. michael.

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