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June 28, 2017

Swab Culture is Inaccurate Test for Determining Tonsillitis

A fascinating study came out in June 2017 that compared the bacteria found on the tonsil surface by swab versus bacteria found within a core needle biopsy versus bacteria found within the dissected tonsil's core. The take home finding is that a swab culture poorly identifies the bacteria causing recurrent tonsillitis.

Based on 54 children who underwent tonsillectomy, researchers performed a swab, needle biopsy, and core dissection of all tonsils removed. Culture results obtained from all three different methods of sampling were than compared.

The infectious agent obtained from the dissected tonsil core is considered the most accurate to which  the other two methods (swab and needle biopsy) are compared.

What they found was that:

• Culture results obtained from the three methods were in agreement only 63% of the time.
• 16.7% of the surface swab cultures grew something different from pathogens obtained via the other two methods.
• In another 5.6%, the surface swab culture came back negative while the two core cultures were positive for the same pathogens.
• The results of needle biopsy culture and dissected core culture were in agreement 85.2% of the time.
• In only 7.4% did the core needle biopsy culture fail to accurately identify the infectious agent.
• Overall, the sensitivity and specificity of core needle biopsy sampling was 100 and 50% respectively, compared with 82.9 and 30.8% for the superficial tonsillar swab.

In conclusion, getting a swab culture of the tonsil provides the wrong answer not uncommonly.

Obtaining a core needle biopsy provides a more accurate answer to the putative infectious agent, but I doubt that this more invasive test is something that can be tolerated in children in the office, especially given kids already HATE getting just a simple swab done.

As such, although the swab culture is unlikely to go away in the near future even though it's accuracy is questionable, one should consider the results only as a guide rather than a statement of fact and greater weight should be given to clinical findings in deciding whether a presumed tonsil infection is present or not.

Interestingly, the most common organism found in this study was staph aureus... not strep. Keep in mind that rapid strep tests can ONLY say whether strep is present or not... it doesn't tell whether any other organisms are present or not. Other organisms found include Klebsiella, Moraxella, Enterococcus, coagulase-negative staph, pseudomonas, and E coli.

While we are on topic, watch this video explaining why it takes several days to get culture results.


Reference:
A comparison of tonsillar surface swabbing, fine-needle aspiration core sampling, and dissected tonsillar core biopsy culture in children with recurrent tonsillitis. Ear Nose Throat J. 2017 Jun;96(6):E29-E32.



Fauquier blog
Fauquier ENT

Dr. Christopher Chang is a private practice otolaryngology, head & neck surgeon specializing in the treatment of problems related to the ear, nose, and throat. Located in Warrenton, VA about 45 minutes west of Washington DC, he also provides inhalant allergy testing/treatment, hearing tests, and dispenses hearing aids. Google+ Christopher Chang, MD Bio

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