Group A Streptococcus (GAS): Diagnosis

by John Fisher, MD

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    00:01 So, turning now to how do you actually diagnose group A streptococcal pharyngitis.

    00:10 Well, since the 1960s, physicians in primary care have been employing the Centor criteria and they have been modified as follows: It’s actually a scoring system to help a physician determine whether to get a throat culture and whether to use antibiotics.

    00:34 So if the patient is from 3 to 14 years of age, then as you can remember, group A strep is likely, so they get one point for that.

    00:45 If they’re 15 to 44, it’s sort of comme ci, comme ça, they don’t really get a point.

    00:54 If they’re over 45 years of age, then of course group A strep becomes less and less common and you take away a point, they get a minus one.

    01:06 If on exam you find the exudate or swollen tonsils, you give them a point.

    01:13 If they have tender or swollen anterior cervical nodes, they get another point.

    01:19 If they have fever more than 38, they get another point.

    01:24 And remember this, if they do not have a cough, they get a point, but if they have a cough present they get nothing.

    01:36 So how do you use this scoring system? If their added up score is minus one or one, their risk of group A strep is less than 10% so they should get no antibiotic and no throat culture.

    01:54 We could save a lot of money and save a lot of allergic reactions if we would follow that.

    02:01 If they have a score of two or three, their risk of strep is between 15% and 32%, still pretty low, but possible, so you get a throat culture, but you wouldn’t give antibiotics until you found the results of the throat culture.

    02:21 And if it’s group A strep, you then treat them.

    02:25 You still have some time, you really have up to ten days to prevent the sequelae of group A strep, so you can wait for the culture.

    02:38 If they have a score of four or five, their risk of group A strep is not 100% by any means, it’s only 56%.

    02:48 You would certainly then go ahead and either do one of the rapid strep screens or culture and give antibiotics if positive.

    02:57 And I want to emphasize the current recommendations of the Infectious Disease Society of America.

    03:05 Empiric treatment is no longer recommended just on the basis of symptoms alone.

    03:13 And the other thing about antibiotics, let’s say a patient has had three days of a sore throat and it’s caused by group A strep.

    03:25 If you give antibiotics after three or four days, the antibiotics don’t do anything for the symptoms, so you’re not going to hasten the resolution of the symptoms.

    03:36 Yes, you will eradicate strep from the throat, but you have to really -- To get any resolution of symptoms, you’ve got to start antibiotics within the first 24 hours ideally.

    03:49 So there’s no rush if the patients had several days of symptoms, you can wait to get the culture, and you can wait up to ten days to prevent the sequelae.

    04:03 A throat culture is very sensitive and very specific for group A strep.

    04:10 The microbiologists deal with this organism all the time and they can recognize it quickly.

    04:17 There are rapid antigen detecting systems.

    04:21 They have a decent sensitivity from 70% to 90%, not as good as culture, but their specificity is about the same as the culture.

    04:32 And here you’re showing group A strep growing on blood agar and there’s a zone of inhibition around a bacitracin disk in most cultures, not particularly shown in this one, but you can see the beta-hemolysis.

    04:56 So the goals of treatment then for group A streptococcal infection, and really that’s the main one we’re focusing on, is resolution of symptoms and you need to start early as I mentioned.

    05:11 This also is a contagious disease, so the earlier you start, the less contagious the patient will be.

    05:20 And if you can start within ten days you can reduce the risk of complications.

    05:28 So what is the treatment? Well, it’s my favorite antibiotic, penicillin, and in the form of oral penicillin it would be penicillin V or amoxicillin.

    05:39 And we generally use a ten-day course because that’s generally required to get rid of strep from the pharynx.

    05:48 Remember, amoxicillin given to somebody with infectious mono could cause a rash.

    05:53 If a patient has a penicillin allergy, then we prescribe Azithromycin, Clarithromycin or Clindamycin.

    05:59 And there are intramuscular regimens in patients that really can’t take oral medication for some reason, you can give them a dose of long-acting benzathine penicillin G dosing according to their kilogram weight.

    06:17 If they do have that dreaded anaerobic infection Fusobacterium necrophorum, we’ve got to use something that is very good for anaerobes and we will probably hospitalize these patients because many of them are sick.

    06:34 And it’s recommended that they get ampicillin/sulbactam.

    06:39 Now, the sulbactam is a beta-lactamase inhibitor, it’s what you call a suicide beta-lactamase inhibitor.

    06:47 It will remove all of the beta-lactamase produced by this organism out of the system so that ampicillin, which it’s attached to, can go do its thing on the bug.

    07:01 Many people recommend that you add metronidazole for extra anaerobic coverage because it tends to penetrate clots.

    07:08 I’m not certain whether you absolutely need to use metronidazole, but that’s what’s recommended.

    07:16 For Corynebacterium diphtheriae, you can remove the organism in somebody with active diphtheria with penicillin.

    07:27 But to actually get rid of somebody who’s simply colonized, penicillin won’t work, a macrolide is needed.

    07:33 So we talked about the complications that we’re trying to prevent and these are they.

    07:41 A peritonsillar abscess doesn’t have to be caused only by Fusobacterium, but can be caused by group A strep.

    07:49 You can have these dreaded parapharyngeal space infections, which can involve the dangerous areas of the head and neck.

    07:59 Lymphadenitis, sinusitis, and otitis media can result, and mastoiditis in very serious complicated otitis.

    08:11 Necrotizing fasciitis is pretty rare, and so in this case, we would be talking about necrotizing fasciitis of the soft tissues of the neck.

    08:25 Group A strep can produce the toxic shock syndrome which is characterized by diffuse erythema of the skin with desquamation, hypotension, and it can result in multi-organ failure, and this is caused by a cytokine storm, which the organism can result in liberating from phagocytic cells.

    08:56 There are some non-suppurative complications, as well.

    09:01 The most dreaded of course is acute rheumatic fever and rheumatic heart disease.

    09:07 And back in the days before antibiotics were available, this was a very common problem.

    09:12 Because group A strep was common, we couldn’t treat that.

    09:15 There were no antibiotics, so we looked at a lot of the complications.

    09:20 Another complication, which is fortunately not so common, is that of acute glomerulonephritis.

    09:28 And here I’m showing, on the left hand picture, what a normal glomerulus looks like, a tuft of glomerular capillaries.

    09:38 And I think you can see how busy the glomerulus is in acute glomerulonephritis and how cellular it is.

    09:48 What you’re really looking at is neutrophils that have responded to antibodies that are located in the glomerulus, and they’re causing essentially destruction of that glomerulus.

    10:02 And this brings me to the end of my discussion about pharyngitis.

    10:06 I hope that it’s been helpful to you.

    About the Lecture

    The lecture Group A Streptococcus (GAS): Diagnosis by John Fisher, MD is from the course Upper Respiratory Infections. It contains the following chapters:

    • Diagnosis – Group A Streptococcus
    • Acute Pharyngitis – Management
    • Acute Pharyngitis – Etiology

    Included Quiz Questions

    1. Ruling in disease if test is positive
    2. Ruling out disease if test is negative
    3. Making a definitive diagnosis
    4. Determining antibiotic sensitivity
    5. Determining severity of disease
    1. Obtain a rapid antigen detection test
    2. Initiate antibiotics
    3. Obtain blood cultures
    4. Prescribe acetaminophen
    5. Refer for hospitalization
    1. Less than 10%
    2. 15-32%
    3. 50-55%
    4. 60-80%
    5. No risk
    1. -1
    2. 0
    3. 1
    4. 2
    5. 3
    1. A 10-day course of oral penicillin
    2. A 10-day course of erythromycin
    3. Throat cultures and confirmation of diagnosis before prescribing antibiotics
    4. A 5-day course of oral penicillin
    5. A single intramuscular injection of long acting penicillin followed by a 14 day course of oral antibiotics
    1. Delaying the treatment for as long as possible.
    2. Decreasing risk of transmission of the disease
    3. Decreasing risk of suppurative complications such as peritonsillar abscess formation
    4. Decreasing risk of rheumatic heart disease
    5. Reducing time to resolution of symptoms

    Author of lecture Group A Streptococcus (GAS): Diagnosis

     John Fisher, MD

    John Fisher, MD

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    Amazing lecture!
    By julia p. on 26. August 2017 for Group A Streptococcus (GAS): Diagnosis

    very nice explanation and helpful information, thank you for the knowledge shared here

    Straight Forward & Clear
    By Anthony M. on 23. August 2017 for Group A Streptococcus (GAS): Diagnosis

    This guy is very straight forward and clear. Very Helpful.