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. Research in 2019 confirms these findings.

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.

In another study, the most frequent bacteria found in recurrent tonsillitis was Haemophilus influenzae, followed by Staphylococcus aureus and Streptococcus pyogenes.

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

Watch a video showing how a tonsillectomy is performed here!


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. 

Bacteriology of the Tonsil Core in Recurrent Tonsillitis and Tonsillar Hyperplasia - a Short Review. Acta Oto-Laryngologica, 120:543, 206-208, DOI: 10.1080/000164800454404

Tonsillar surface swab bacterial culture results differ from those of the tonsillar core in recurrent tonsillitis. Laryngoscope 2020 Dec;130(12):E791-E794. doi: 10.1002/lary.28403. Epub 2019 Nov 20.