Group A Strep: The Stray Dog of Bacterias

In Medical Concepts by Brent Thoma2 Comments

Sore throat. Group A Strep. It’s a presenting complaint we see almost daily that certainly doesn’t get anyone’s heart racing.

I feel comfortable identifying the “sick” child, have a well-practiced “it’s a virus” speech, am adept in the art of the parent-facilitated tonsil swab, and generally think I diagnose and manage these patients fairly well. For a discussion of the Modified Centor Score and helpful PV card, see Academic Life in the EM.

I feel less comfortable with my knowledge of the many strep associated complications, most of which I’ve never seen. This gap was made painfully obvious to me on my most recent in-training exam when I was asked about a case of a child presenting with Scarlet Fever (which I have seen, but got wrong anyways).

Damn. Too much Weingart, not enough EMPEM.

And so, I devote this post to Group A Streptococcus: The Stray Dog of Bacterias. Like a stray dog, it’s generally a harmless annoyance, but every once in awhile it gets rabid and crazy unpredictable. I can think of no other infection that has such varied sequelae.

The rabid manifestations of Group A Strep

Acute Rheumatic Fever (ARF)

This is the big bizarre one with the most prolonged sequelae. It’s thought to be caused by a delayed autoimmune response initiated by the persistence of GAS in the upper respiratory tract following strep pharyngitis and it has been speculated that some serotypes are more “rheumatogenic” than others. While it is now a rare condition in Canada (I’ve never seen an acute case) we won’t catch an outbreak if we’re not vigilant, there are areas where it is still endemic (such as northern Australia), and it’s still on our board exams. Treatment of GAS pharyngitis has been found to prevent the development of this condition.

This article discusses the factors contributing to the decreasing incidence of ARF in North America.  To paraphrase, while environmental (crowding, access to health care), host (response to infection), and disease (decreasing prevalence of rheumatogenic serotypes of GAS that express M proteins correlated with higher levels of ARF) factors have likely played a role, we don’t have a full picture of why the incidence has decreased so dramatically over the past 50-60 years.

ARF is a mean thing to grill med students about because of it has very specific diagnostic criteria that everyone has heard of but nobody can remember because they defy pathological logic (do these presentations seem random and weird to anyone else?). How many of the Jones criteria can you name off the top of your head?  Originally published in 1944, the Jones Criteria were last revised by the AHA in 1992. They include:

Five major manifestations:

  • Migratory arthritis
    This tends to be one of the earlier symptoms and generally migrates to new joints within a few days, NSAIDS put an end to it quickly, and the synovial fluid is inflamed but sterile.
  • Carditis and valvulitis
    Can basically inflame the entire heart (pancarditis), various ausculatory findings depending on pericarditis and the valve(s) affected (generally mitral +/- aortic regurg), valve damage can progress chronically over years leading to the elderly patients that we see with CHF and valve problems.
  • Central nervous system involvement (eg, Sydenham chorea)
    Described as involuntary, abrupt, nonrhythmic movements with weakness and emotional disturbances… Presents late
  • Erythema marginatum
    Thank you google images
  • Subcutaneous nodules
    Firm, painless symmetric nodules measuring <2cm located over bony surfaces or tendons. These are the least common, come early and leave fast.

And four minor manifestations:

  • Arthralgia
  • Fever
  • Elevated ESR or CRP
  • Prolonged PR interval

Diagnosis should be suspected with a GAS infection followed by 2 major criteria or 1 major and 2 minor criteria. Unless the major criteria is chorea or carditis alone, in which case only that criteria is required. And if you’re too strict with the criteria you may underdiagnose it. I will never remember all of this this. Maybe someday there will be a PV card so I don’t have to!

Unfortunately, the delayed presentation means that throat cultures and rapid strep tests are generally negative by the time of presentation so they are unlikely to be useful for confirming a preceding GAS infection. Various serologic tests (ie. antistreptolysin) can be sent, but their interpretation isn’t totally straight-forward and is likely best left for those doctors downstream from the emerg.

Scarlet Fever

I’m horribly embarrassed that I got a question about this wrong on my in-training exam. Back to the basics.

Scarlet fever is basically strep pharyngitis + rash and is diagnosed and treated in the same way. The rash is caused by a delayed skin reaction to an exotoxin produced by GAS and generally described as having a “sandpaper” quality. It generally starts at the top (head/neck), can cause strawberry tongue, moves down to the extremities sparing the palms and soles, and can desquamate. Thanks again, Dr. Google.

Toxic Shock-like Syndrome

As this savage condition is a possible complication of GAS pharyngitis that can be deadly I feel it warrants a mention. However, as its more commonly associated with invasive infections (ie. pneumonia, bacteremia, necrotizing myositis/fasciitis), I’ll leave it to the sexier blogs.

Post-streptococcal Glomerulonephritis (PSG)

Yet another post GAS pharyngitis complication, this one is thought to caused by the deposition of antigens into the glomerulus where they are bound by antibodies causing glomeruloneprhitis.  While its prevalence has drastically decreased in North America, it is still quite prevalent in third world countries and parts of Australia.

Presentation generally follows 1-3 weeks after pharyngitis and can vary from microscopic hematuria to gross hematuria/proteinurea/HTN/edema/elevated creatinine. An abnormal urinalysis with these findings and a recent infection hints at this. As the patient usually presents late, cultures are as useful as they are for ARF.

Prevention is possible with early, effective antibiotics for GAS (or is it? please see the addendum) and PSG should be treated as if they had an active infection because they may still be colonized even if an infection is not evident, it may help to prevent the spread of the nephritogenic strain, and it may decrease the severity of the clinical course. Data on the long-term prognosis is lacking, but several case series following children for up to a8 years found relatively low rates of potentially related complications (<20% had abnormalities on urinalysis, <15% had hypertension and <1% had an elevated SCr). Findings have been less optimistic in adults.

PANDAS

AKA “Pediatric autoimmune neuropsychiatric disorder associated with group A streptococci.”  Who knew? GAS can even exacerbate OCD and tic disorders. Is there anything it can’t do? Anyways, I’m going to leave this topic alone because I think I’m about as likely to see it as I am to see one of these giant Chinese teddy bears in the wild.

Suppurative Complications

In addition to all of the complications described, GAS can cause all sorts of suppurative complications – think cellulitis, otitis, sinusitis, peritonsilar abscess, meningitis and fasciitis. I may discuss some of them separately at another time.

Conclusion

That’s it for this week! It was a bit more serious than some of my other posts, but I hope you found reading it as helpful as I found writing it. I’d greatly appreciate any feedback and topic suggestions.

Thanks again to everyone who has read and tweeted about my blog. I’m quite excited to continue contributing to the FOAM world that has already taught me so much.  Happy New Year!

Addendum

Please see an expanded post on the treatment of GAS Pharyngitis with antibiotics that I made after the below comment from Dr. Lars Peterson.

Brent Thoma @boringem

Additional References:

Uptodate’s various articles on GAS and its complications directed me to several of my references and was used along with Rosen’s for background information

Brent Thoma

Editor at CanadiEM
Dr. Brent Thoma is a medical educator, blogging geek, and trauma/emergency physician who works at the University of Saskatchewan College of Medicine. He founded BoringEM and is the CEO of CanadiEM.