Why your strep culture might be neg

[EAMom]

Hi Colleen,

 

The original littleDaniel post is now in tic/tourettes so I am resposting here. In addition to the original reasons I thought of (below) I have also learned that probiotics and certain herbs may interfere with culture results. Also, Buster tells me that intracellular strep is more difficult to culture. This makes sense as our daughter had very severe PANDAS symptoms while her culture was only "rare" growth after 72 hours.

 

Also, just to remind, a culture done while on antibiotics or too soon (less than 3 weeks) after stopping antibiotics may likely result in a false negative result.

 

Hi Collen,

 

Several possiblities for neg culture (yet actually has strep):

 

1) Most (sorry, don't have the reference handy but could find later when time allows) people will "fight off" a strep infection after about 2 weeks even if there are no antibioitics. (This was not the case with dd, still cultured positive after 2 mo.) Of course, a child could still have behavior changes (eg. brain inflammation, ongoing immune response) even though the "trigger" (strep) is gone.

 

2) Some strains of strep are anareobic...so unless the strep is cultured correctly (blood agar actually "punctured") the strep will not grow.

 

3) Just a rapid is done or the culture is only grown overnight, not 72 hours. (My dd had rare growth after 72 hours.)

 

4) Culture swab not done correctly (didn't get a good sample) on an uncoorperative child.

 

5) I don't know if anyone has any more ideas?

[Chemar]

Hi

if any threads need to move over here that I may have missed as not primarily about PANDAS please feel free to let me know via PM and I will move them over. If overlap areas I can leave redirect on the TS/tics forum so folks can find them easily at both

 

[colleenrn]

EAMom,

Thank you so much for your reply and information! It has been SO puzzling to me over the years of getting cultures back negative (yes we do 72 hr. cultures YET the lab has messed up several times and read and discarded the culture after 36-48 hrs.) when I KNEW my daughter had strep and then having it confirmed even more that she had strep as I saw her greatly improve once we began a course of antibiotics. I have SO many questions if anyone has any answers.

If intracellular strep is more difficult to culture, is there anything that I can do to insure a correct culture? I make sure the nurse gets a good sample from both tonsils and make sure they culture it for 72 hrs. Is there any reference that you know of that talks about intracellular strep being harder to culture? The longer they have untreated strep, the more likely it is to become intracellular? If strep goes untreated and the body fights it off, what happens to the antibodies if antibiotics are not given? Wouldn't they continue to attack the brain, causing PANDAS symptoms?

You mentionned that some strains are anaerobic and difficult to culture if the agar is not punctured. Is this just something that the lab has to do correctly or do we have to request anything special?

When I have a culture done, will they automatically test for all strains or just Strep A? How do I get them to specifically test for any strep at all and not just strep A? There was a time my son's culture came back as "non A strep" and I saw and increase in his behaviors and he responded well to antibiotics. The lab did not specify, however, what the strep was.

Thanks so much, Colleen

[Buster]

Hi Colleen,

 

Can you provide a bit more history? EAMom is absolutely right that there are strains of strep that do not grow in air and thus have to be specially cultured with a puncture rather than surface wipe. There are also strains of strep that produce an uncharacteristic growth pattern that can easily be missed if the test itself was for group A Beta-Haemolyitic strep. However, these are very rare and it sounds like you had other ways of confirming strep infection.

 

For odd cultures: http://icmr.nic.in/ijmr/ijmr_supp/4.pdf

For interference for GABHS: http://archotol.ama-assn.org/cgi/reprint/125/5/552.pdf

For intracellular strep: http://jmm.sgmjournals.org/cgi/reprint/49/6/499.pdf

 

Of course the Kaplan papers are also quite good if you'd like me to repost those.

 

Regards,

 

Buster

[EAMom]

Hi Colleen,

 

hopefully Buster's links were helpful.

 

According to the NIMH website PANDAS is just from GABHS, doesn't mention other streps. I supposed it's possible other streps are involved and it just hasn't been studied yet. It's also possible your son is having more of a PITAND reaction.

 

I do know that strep carriers are more likely to have intracellular strep. I think it is an individual thing (probably genetic) but also dependent on the strain of strep. It makes sense that if strep is hiding inside epithelial cells, perhaps in somewhat low numbers, that it would be harder to get a positive culture. If the throat is red/inflamed (acute pharyngitis) it is easier to get a positive culture since the strep is actively replicating (plus lots of it) and on the surface of, not inside of cells.

 

Another way to look at it...someone with active pharyngits (acute, red sore strep throat) is much more contagious than an assymptomatic strep carrier. There's more strep bacteria "flying around" to infect others. However, it is possible for a strep carrier to infect others, usually someone they spend a fair amount of time with, like a family member or a friend at a sleepover (we did that to a friend in early March).

 

I'm not sure about your answers about the lab, it might depend on the lab...that's one you might have to ask your doctor or lab about and hopefully they will know what you are talking about!

 

I would think if a PANDAS child doesn't have a current strep infection then I would think the antibodies (or whatever is causing the PANDAS) would eventually just "fizzle out"....although this may not be the case with repeated episodes? Perhaps the child's immune system becomes altered and this is why some kids seem to stop responding to antibiotics and need IVIG. That's my theory at least.

[EAMom]

Throat culture could also be Negative due to other sources of GABHS: eg: sinuses, skin, rectal.

 

The above information is from a very interesting review article on PANDAS http://jcn.sagepub.com/cgi/content/abstract/21/9/727 . I don't know if the full text is available online for free. (We have the full text, I think dh paid to get it. )