Strep Throat Diagnosis
Fall and winter always bring with them an increase in the number of strep throat cases I see each day. Some patients truly have strep throat, and some don’t. So, how can you tell the difference?
“Strep” throat is a term widely used by non-medical lay persons to mean “I’m having throat pain and I think I need antibiotics”. But true strep throat is a bacterial infection caused by a little spherical, gram-positive bacterium that grows in a chain pattern and can cause infection not just in the throat, but also in the heart, kidneys, and skin. In fact, left untreated, streptococcal throat infections can, in rare cases, lead to permanent heart and kidney damage.
Strep and other bacterial throat infections are painful, cause fevers (core body temperature greater than 100.5 F), and usually require antibiotics as the definitive treatment. Viral throat infections can be painful, can cause fevers, and never require antibiotics as time is the definitive treatment for most viral infections.
So, how can you distinguish between bacterial and viral infections?
You could purchase strep throat tests, available here. These are very specific and sensitive throat swab tests that can help you diagnose strep throat infections. Also, they are available without a prescription.
If the test result is positive, it’s a done deal. However, if the result is negative, and you or your patient are feeling rough, what physical exam and diagnostic pearls are available to help cinch the diagnosis?
The Centor score is one method. It assigns a point each to five different criterion.
- Can’t cough
- Exudates (white blemishes on the tonsils)
- Nodes (enlarged lymph nodes on the front of the neck)
- Temperature (fever greater than 100.5 F)
- OR (young or old patient)
If a patient has 4 out of the 5 criteria, you can presume they have strep throat. Less than that, and they very likely have a viral throat infection.
Another method is taking a good history and performing a great physical exam. Here are some questions to ask.:
A no answer to this question almost always means the throat pain is viral or caused by allergies:
- Have you had any fever or chills?
Yes answers to these questions normally indicate a viral throat pain:
- Have you been coughing?
- Did your throat pain begin after you started coughing?
- Are you having any nasal congestion?
These questions can probe more deeply and their answers can steer the diagnosis wagon:
- Which began first, the throat pain or the coughing?
- If you’re not coughing, have you been clearing your throat a lot because of sinus drainage?
If your patient has any type of sinus congestion, drainage can go down the back of the throat (post-nasal drip) and cause moderate to severe throat irritation that can mimic a bacterial throat infection. If your patient has no sinus involvement and has only throat pain, then it is more likely a bacterial throat infection.
Part of confirming the absence or presence of sinus drainage is to actually look at the patient’s throat. Do they still have tonsils? If so, what size and color are they? Do they have white blemishes on them, like the tonsils in the picture above? Do they have a really foul smelling breath?
The bottom line here is that if you look at your patient’s throat (or your own throat in the mirror) and see a red, swollen, angry throat without snot globs at the very back, that’s a plus one for strep. If you run your fingers along their neck and feel a few swollen lymph nodes on either side, that’s a plus one for strep. If they also have a fever, diagnose a bacterial throat infection that is likely strep (since you can’t prove it without doing a culture in a lab).
If they don’t look and sound like the above, they presumably have a viral throat infection.
Strep Throat Treatment
You’ve reached a diagnosis. Now, how do you treat?
The gold standard for treating confirmed strep throat, according to the Infectious Disease Society of America, is to treat kids and adults alike with amoxicillin at 50mg/kg (milligrams per kilogram of body weight) up to 1,000mg once daily for 10 days.
If you’re not treating confirmed strep, use that dosage but make it twice daily.
Amoxicillin is a prescription medication. But, the same exact medication you or I would take, down to the manufacturing lab, is available in a fish antibiotic that does not require a prescription.
For patient’s who are penicillin allergic, and amoxicillin is a penicillin, use cephalexin. The dosage for both kids and adults is 50mg/kg every 12 hours up to 500mg per dose.
Viral infections are a lot more simple to treat. Gargling salt-water every couple of hours will significantly reduce throat pain and swelling. We used to recommend taking naproxen sodium (Aleve) or ibuprofen with viral throat infections for those same reasons, but we now know that these can increase the risk of heart disease in some patients, especially those with personal or family history of heart disease. It’s better to take acetaminophen (Tylenol), up to 1,000mg every 6 hours. Then, ride out the storm because almost all viral illnesses are self-limiting.