Streptococcus pyogenes is another one that I'm going to create a presentation for you because it's one of these skin and soft tissue bugs that actually causes a whole bunch of different diseases. And so it's easier to find, to kind of put it together for you in one presentation than try to find a bunch of videos online. And there isn't much actually because I did look to see if there was something more fun that people had put online about streptococcus pyogenes.
Streptococcus pyogenes, the name comes from the Greek, so pyo stands for pus forming or pus. And so this is one that you tend to associate with pus. It's a streptococcus, so coccus are these round, but you notice that the bacteria are a cocci, but they're in strips. So strepto is strip, so it's sort of these chains of cocci-like bacteria. Streptococcus pyogenes is a member of group A strep, so they classify streptococcus based on the surface proteins of the bacteria and so you may have heard of group B strep.
In fact, if you've had a baby or you've been close to some who's having a baby and they were tested for strep before birth, they were looking for group B strep. So Streptococcus pyogenes, this particular species, is actually a member of group A strep. And it's a gram-positive cocci, similar in that way to Staph aureus. It grows in chains, so in that way it's different. Staph aureus grew in grape-like clusters.
And Another way that it's different is that it's not normally part of the microbial skin community, but we do see it in about 5 to 15 percent of children and they're typically asymptomatic carriers of the organism. This particular bug causes a disease that ranges from really mild superficial skin infections to life-threatening systemic diseases, and that's the reason it's a part of our disease of the day. a group of organisms. Good news, unlike Staph aureus, it remains highly sensitive to penicillin.
So if you get a streptococcal infection, it's treatable. We don't see the kinds of resistance that we do with Staph. There are about 700 million group A strep infections worldwide every year.
The mortality rate overall is quite low, 0.1%, but 650,000 of these cases are severe. and they have a mortality rate in that group of 25%. So it's really important to recognize Streptococcus pyogenes infections early and treat them since antibiotics work so effectively and make sure that these kinds of infections don't develop into these more severe and life-threatening forms. This is a great time to review what we mean by primary and secondary.
Some pathogens are primary pathogens. We say that they make Healthy people sick. These skin bugs like staph and strep, they can make healthy people sick, but we often see them as secondary infections. So for example, this is a great example here.
This is a child, this picture is a child who had the chicken pox. So you can see her little chicken pox sores here. And she's scratched one of these chicken pox.
Likely they itch. This is probably how this happened. And you see that right here what she's got now is a Streptococcus pyogenes infection.
And it's secondary to the chicken pox, which means that it wouldn't have happened if she hadn't have had the chicken pox first. So this particular child has developed actually a severe infection. This redness you see around here is called cellulitis. It's a deeper tissue infection.
So the organism has migrated from where it was introduced under the skin. And it was necessary in this particular case to go in and surgically debride the area because the physicians were worried about the development of something called necrotizing fasciitis. And they wanted to prevent that. So this child, what her parents probably thought was going to be a mild case of the chicken pox, turned into... surgical removal of tissue here to protect her from a more serious infection.
And this is actually a really good time just to talk about chickenpox. There are lots of people who feel that chickenpox is a very mild disease. There's a vaccine available. A lot of parents don't feel like the vaccine is necessary or they might feel that their child is better off getting the infection the natural way and developing immunity that way. But it's really important to point out that the reason we develop vaccine is because even though most children have a mild course of chicken pox, what can happen is something like this where it ends up being a whole lot more serious and this child could have died from necrotizing fasciitis.
So the good news is that I believe she did fine but it required a pretty serious intervention. Now streptococcus pyogenes can also cause primary infections, and so you've probably heard of strep throat, and that's a really common primary infection. It takes a healthy person, they end up with streptococcus pyogenes introduced into their throat, and they can develop a strep throat infection. So here's a laundry list of group A strep infections. So pharyngitis, we're thinking here of things like strep throat.
Remember when we talked about Staph aureus, I mentioned that it can also, that impetigo, which is caused by Staph aureus, can also be caused by Streptococcus pyogenes. If group A strep gets into your lungs, it can cause pneumonia. If it gets deep into your tissues, it can cause anything from, you know, erysipelas to cellulitis to really deep infections like necrotizing fasciitis. If it gets into your blood, it causes bacteremia. It can get into your bone.
If it's from your blood, it can move to the bone or from tissue move to bone and cause osteomyelitis. It can cause ear infections, otitis media. It can get into your sinuses and cause sinus infections. And if it gets into your brain, it can cause meningitis or even a brain abscess.
So this is one of those bugs that can cause infections, and it'll go anywhere it can get to and begin growing and cause, you know, very, very different types of infections, but they're all caused by the same bacteria. Now... You'll recall from the very first week of class we talked about Ignacia Semmelweis and the women who had childbed fever in the Vienna hospital and that childbed fever is also caused by streptococcus pyogenes. We don't really think of it as a huge problem now, much less common because especially in in the United States you know physicians know about hand washing and we don't just pass these infections back and forth to mothers but this is the bug that caused childbed fever and was associated with all that mortality for these women who were giving birth in the Vienna Hospital and other hospitals at the time. So you've probably heard of strep throat and if you're like most people you've had it at one time or another.
The last time I had strep throat I was a senior in college and I'm happy to have not had it since because my my recollection is just how painful it was that every time I swallowed it woke me up. It causes a fever of 101 and then if you suspect strep throat, one of the things that you can do is look in the mirror and you might see these white streaks on the back of your tonsils, which can be in some cases streaks of pus or the organism itself. Sometimes people get little petechiae, these little red spots on the roof of their mouth. Sometimes people have a headache, nausea, vomiting.
You can have swollen lymph nodes, you can have a rash, all common symptoms of strep throat. Good news is they have rapid strep tests. If you think you have strep throat, particularly if you have a fever and you see these white streaks on your tonsils, a really good idea is to go straight to the doctor and have them do a rapid strep test.
And they can test for group A strep within minutes in the doctor's office and then start you on a course of antibiotics if you need them. You know, one of the things that I tend to tell students is, you know, don't take antibiotics unless you really need them. Strep throat is an example of a case where it's always justified to take antibiotics.
One of the problems with strep throat is the complications it can cause. If that bacterium can get into your bloodstream or move to other parts of your body, as we saw on a prior slide, it really is associated with a lot of other infections. And it can actually cause something called rheumatic fever, which I'll talk a little bit more about in a minute.
You really want to minimize the amount of time that you are dealing with a case of strep throat. Now, this form of strep is usually transmitted by direct contact. So kids, we see this in kids a lot because they're around other kids and they don't always wash their hands well.
Not sure what that says about my hygiene when I was a senior in college, but we won't go there. We talked about the symptoms already. So airborne respiratory droplets, coughs, sneezes, saliva, kissing or shared drinks. Well, that could have been college.
All right. So what kinds of antibiotics do we use? Oral antibiotics.
So this one usually works really well and there are others as well. penicillin is something that you might be allergic to for example. Alright so one of the big concerns about Streptococcus pyogenes is the potential to to cause invasive tissue infections which get very very difficult to treat and become life-threatening really fast. So if the organism gets into deeper layers of the tissue, a more superficial rash we refer to as erysipelas, and as it gets deeper and you can see that this is much redder, we have deeper layers of skin involvement that is called cellulitis. Now these are typically very treatable but The concern is that if that organism gets deeper into the tissue, then we associate it with something called necrotizing fasciitis.
And that term is really just a description. So itis is anything with itis at the end means you have inflammation, and the fascia is the lining between the skin and the muscles. And so if you have death of that tissue between the skin and the muscles, you have necrotizing fasciitis.
necrosis means death of tissues. Sometimes this is referred to as flesh-eating disease. And I want to make a point that while streptococcus pyogenes is associated with necrotizing fasciitis, it's not the only organism that's associated with this particular infection. And so you might hear about necrotizing fasciitis and then hear another organism as the cause, and that would be not uncommon at all. When you get this kind of infection, what it results in is the death of soft tissue.
So everywhere it's turning black here, we're looking at tissue dying. And if the muscles and tissue begin to die extensively, then you can lose that tissue or lose that limb as a result of it. And of course, if the infection spreads and gets in your bloodstream, you can end up with septic shock and you can die from that as well.
We treat necrotizing fasciitis with antibiotics and surgery. Usually we have to at least remove some tissue. Sometimes we have to remove a limb as well. And the risk of death once this infection proceeds to necrotizing fasciitis is actually very high, 25% to 35%. So the goal is to prevent necrotizing fasciitis from beginning in the first place by intervening early.
And again, I will say that this is one of those infections where the use of antibiotics early is warranted. We don't let even a strep throat infection go if we know someone has it. this particular organism.
Now, Streptococcus pyogenes can also make some toxins. We mentioned last time about Staph aureus making toxins that cause food poisoning. Streptococcus pyogenes makes toxins as well and one of the toxins results in a disease called scarlet fever which you may have heard a lot of reading about people in the nineteen hundreds, you know, in the United States. Scarlet fever was a fairly common infection.
It's really just streptococcus pyogenes, but it's a strain of this organism that makes a toxin. And when that toxin gets into your bloodstream, it causes this rash. And the rash is the result of the toxin is called an erythrogenic toxin. So it causes this red rash and scarlet in color, very distinctive.
And so that's why they named it scarlet fever. But again, this is the same bacterium. It's just a version.
that can make this toxin and this can happen as a result of initially what would have been a strep throat infection. Streptococcus pyogenes is also associated with toxins that can induce a very highly overactive immune response. So in addition to this erythrogenic toxin that is the cause of scarlet fever, some strains of streptococcus pyogenes make this.
toxic shock toxin. And this particular toxin, when it gets released into your bloodstream, it causes your immune system to overreact. And that results in lots of symptoms like a really high fever, lots of T cells proliferating, dividing, and being released. Lots of these immunological mediators called cytokines flooding your bloodstream.
And they can cause your blood pressure to crash, which can cause you to die. It can cause headaches, seizure. but these can make you very very sick extremely quickly i didn't mention this when we talked about staph aureus but actually both staph aureus and streptococcus pyogenes are associated with these super antigen toxins and uh... one of the ways that this has been sort of described in the media is associated with tampon use so if a woman uses a really super absorbent tampon and leaves it in for extended periods one of the things that can happen is bacteria on your hands can end up on the tampon and then that's a really lovely place to grow if you're a bacteria. It's rich in blood, it's like sort of growing them on really rich media and while they're there the bacteria can then if they're the right strain they can produce a toxin which gets into your blood stream and so that's one of the reasons why when tampons are used that we always encourage people to change them regularly and don't leave them in for long periods of time even if it's convenient it's it's actually not safe because of the potential for some of these bacteria that are on your hands and skin to end up on that tampon and then begin dividing and produce a toxin.
About three weeks after a strep throat infection, sometimes people develop something called rheumatic fever. And this is the result of the antibodies that your body made to fight off the strep infection. Then after you've gotten rid of the bacteria, those antibodies occasionally will turn against the host and they will attack your tissues, particularly tissues like heart valves and in your joints. Some of these antibodies can actually damage your kidneys, sometimes permanently.
We call this post-streptococcal glomerulonephritis. kind of a mouthful. So this is another really important reason why we want to treat people with something mild like a strep throat with antibiotics because we know that this organism can actually continue to do damage even after your body has cleared the infection. Group A strep is very common in the US and most of the time it's really not that big a deal.
We have over 10 million non-invasive group A strep infections things like strep throat and mild skin infections But we also do see about 10,000 cases of invasive group A strep So things like toxic shock syndrome and necrotizing fasciitis, which can be very serious There are some seasonal effects of group A strep. So because it's spread by respiratory droplets we see it more commonly in winter and early spring when people are inside and and more prone to be coughing and sneezing with other diseases as well like viral infections. We see skin infections more commonly during the summer when your skin is exposed and you're more likely to get cuts and bruises and things like that.
Just a few more things on the epidemiology of Streptococcus pyogenes. Some of the strains of Streptococcus that are associated with severe invasive disease like necrotizing fasciitis appear to becoming more virulent over time. So even though, you know, we have ways to treat strep with antibiotics, the organism itself is not static. It's evolving and changing, and we see a lot of these more dangerous strains over time. The cases of rheumatic fever are decreasing, particularly in places where we know to get antibiotics on board quickly.
It's still a much larger problem, rheumatic fever, in developing countries. We see group A strep infections all over the world, so I focused on some of the U.S. data, but We see it all over the world and in people of all ages. It's higher in small children.
They have many opportunities for being exposed and typically have little immunity. So again, not a big surprise. I mentioned that there are rapid strep tests.
So here's a picture of a Group A strep test kit. So very, very easy to detect quickly. If someone has strep, they do a quick throat swab and they look for the binding of antibodies. to the bacterial surface. This is a phenotypic test, so you're looking at something specific to the bacteria itself, which is the proteins that are expressed on the surface of the organisms.