Confused about Rapid Strep vs. Throat Culture

Trauma Columnist · Oct 13, 2007

I think this is a case for treating the pt versus the lab result. The rapid strep test is a screening tool. If there is strep present in large enough quantity then it will be positive. However, it is very conditional on the pt obtaining the swab, letting it incubate for 2-3 minutes, etc.. I would probably have not done a rapid strep at all - just treated the child.

Editorial Team / Admin · Oct 13, 2007

Okay, I'm an FNP student and in my peds clincial last week we did a rapid strep on a child (who looked and smelled like he had strep--beefy red throat, white patches on tonsils, fever) but the rapid strep came back negative. So, I said to my preceptor (an MD) are we going to do a throat culture now? He said the rapid strep is a throat culture and that even though it's neg he's going to tx for strep because in two days the rapid strep will be positive anyway. His mind was made up this child had strep. He looked at me like I was crazy for wanting to do a culture.
So now I looked like a fool and am totally confused here. I thought neg rapid streps were always confirmed with a culture? I thought they were different things. Are rapid streps the same as cultures? Can anyone shed some light on this for me?

You are correct, BChapp

Rapid strep is a dx test to test for the presence of strep bacteria. If negative, best case scenario - there should be a followup with a throat culture.

But, as traumaRUs states, many treat based on clinical presentation only.

Ideally, the practitioner should wait for a postive culture before begininning antibiotic treatment. Rationale: (1 reduce overuse of antibiotics (2 allow body to build up its own resistance.

I utilize rapid strep and treat based on clinical presentation.

core0 · Oct 13, 2007

You are correct, BChapp
Rapid strep is a dx test to test for the presence of strep bacteria. If negative, best case scenario - there should be a followup with a throat culture.
But, as traumaRUs states, many treat based on clinical presentation only.
Ideally, the practitioner should wait for a postive culture before begininning antibiotic treatment. Rationale: (1 reduce overuse of antibiotics (2 allow body to build up its own resistance.
I utilize rapid strep and treat based on clinical presentation.

In adults there is a fairly nice algorithm. Also the new assays (if done correctly) are probably as accurate as the culture.

Here is a nice ACP paper on Strep in adults:

http://www.annals.org/cgi/content/full/139/2/150

Here is a nice paper from pediatrics that looks at the different strategies:

http://pediatrics.aappublications.org/cgi/content/abstract/101/2/e2?ijkey=0ba9458b8a8058f43eca1b38d6460643279593c3&keytype2=tf_ipsecsha

Here is the algorithm that I use:

http://www.fpnotebook.com/ENT56.htm

I add another point in immunocompromised patients (no real data to support this). So it only takes two points in a child or three points in an adult to trigger antibiotics. Peds patients who are immunocompromised and have exposure get abx with any pharyngeal symptom. If they have fever they get bigger guns.

David Carpenter, PA-C

Editorial Team / Admin · Oct 13, 2007

Thanks, David. Excellent algorhithm. I've utilized the same.

caldje · Oct 13, 2007

Either the use of guidelines or the use of the rapid screen with a followup culture if negative have proven to be cost effective options with the later being the most acurate (of course) since culture is the gold standard for dianosis. However, when you approach the differences between (1) the use of criteria, such as centor criteria, and a rapid test with (2) the use of rapid test and culture, the people you will exclude from treatment if you use 2 instead of 1 will be very few, likely have a severe pharyngitis, and be very upset if not treated.

Prescribing penicillin/amoxil to that small group of patients will likely not contribute to resistance (especially since there is very little, if any document group A strep resistance to PCN). Then when you factor in cariers, whom you may treat with a positive result when they are actually just carriers, the argument between culture vs. rapid & clinical criteria, becomes pretty moot.

The only real issue here is the folks using macrolides (why does EVERYONE come to the office on zithromax?) when in fact, there is more resistance to macrolides than PCN and those specific macrolides, which could be very beneficial to have in our orificenal, now exhibits rates ofr 20-30% resistance in most areas according to Sanford's guide.

natrgrrl · Oct 18, 2007

I just want to add my two cents. I took my son in for sore throat . The rapid test was negative, doc treated for sore throat and sent us home. No throat culture because he didn't want to "stir up" the infection. I agreed. Several days later my son had a rash and the skin on all his fingers started peeling off. It wasn't just the top layer of skin, one time he handed me this thick piece of skin containing his entire fingerprint! If you haven't seen it, try to imagine what that looks like to a mom.

A week after the first appointment, we went back to the doc for the rash. Doc completely ignored the rash and looked at his fingers, dropped his jaw, left the room (without telling me why) and brought in other doctors.

Obviously, he knew it was Kowasaki disease but it was too late to treat my son by that time. His heart (pericardium?) was inflamed and had fluid surrounding it.

A throat culture would have been very helpful in this case. The only good thing is that I know this doc is not likely to make this mistake again.

prairienp · Oct 18, 2007

Either the use of guidelines or the use of the rapid screen with a followup culture if negative have proven to be cost effective options with the later being the most acurate (of course) since culture is the gold standard for dianosis. However, when you approach the differences between (1) the use of criteria, such as centor criteria, and a rapid test with (2) the use of rapid test and culture, the people you will exclude from treatment if you use 2 instead of 1 will be very few, likely have a severe pharyngitis, and be very upset if not treated.
Prescribing penicillin/amoxil to that small group of patients will likely not contribute to resistance (especially since there is very little, if any document group A strep resistance to PCN). Then when you factor in cariers, whom you may treat with a positive result when they are actually just carriers, the argument between culture vs. rapid & clinical criteria, becomes pretty moot.
The only real issue here is the folks using macrolides (why does EVERYONE come to the office on zithromax?) when in fact, there is more resistance to macrolides than PCN and those specific macrolides, which could be very beneficial to have in our orificenal, now exhibits rates ofr 20-30% resistance in most areas according to Sanford's guide.

Guidelines are great and should be followed. Too bad so many continue to treat because they "think" the patient should be treated. I did the same thing for years, the smell, the look, none of these criteria are as effective as a test.

I stopped using pcn/amox several years ago for + strep screen or culture in my pre-teen-teen early adult groups. Too many cases of concurrent mono.

caldje · Oct 19, 2007

Guidelines are great and should be followed. Too bad so many continue to treat because they "think" the patient should be treated. I did the same thing for years, the smell, the look, none of these criteria are as effective as a test.
I stopped using pcn/amox several years ago for + strep screen or culture in my pre-teen-teen early adult groups. Too many cases of concurrent mono.

I think I mis-spoke a little bit. I didn't mean macrolides, but specifically zithromax. I understand the concerns about tummy upset with e-mycin, but biaxin is effective and safe without the tummy problems.

akoster · Oct 19, 2007

My one reply to why so much zithromax is compliance. People take it once a day and actually finish it.. I'm not even sure how kids take 3 times a day meds if they are in school.

caldje · Oct 20, 2007

My one reply to why so much zithromax is compliance. People take it once a day and actually finish it.. I'm not even sure how kids take 3 times a day meds if they are in school.

amoxil/augmentin can be given BID.