Fusobacterium necrophorum-PCR in pharyngotonsillitis - could the CT-value identify patients at risk for complications?

Background: Previously, we investigated tonsillar carriage of Fusobacterium necrophorum by PCR and found a high tonsillar carriage rate (21%) in asymptomatic 15-25 year olds, but the same age group is most commonly affected by severe F. necrophorum infections. Interestingly, we found Cycle threshold (Ct)-values in asymptomatic carriers to be high (median 29). Possibly, the Ct-value could differentiate between infection and tonsillar carriage, with bacterial load hypothetically being higher on infected tonsils. The purpose of this study was to investigate differences in F. necrophorum Ct-values in patients diagnosed with pharyngotonsillitis who did or did not develop complications.
Methods: Patients with pharyngotonsillitis and positive F. necrophorum-PCR were enrolled from July 2016 - December 2020 in the Skåne Region, Sweden. Patients with prior complications or antibiotics (30 days) were excluded. Data was retrieved from registries and electronic charts. Patients were grouped by presence of any complication within 30 days, defined as a composite score of peritonsillar or pharyngeal abscess, otitis, sinusitis, sepsis or septic complications, chronic or recurrent tonsillitis (after 15-30 days) or hospitalization. Ct-values were presented with median and interquartile range (IQR) and compared with the Mann-Whitney U-test.
Results: In total, 969 patients had pharyngotonsillitis and positive F. necrophorum-PCR. 29% developed complications. There was no difference in Ct-values between patients who did (median 21, IQR 19-25) or did not (median 21, IQR19-26) develop complications (p=0.51).
Conclusion: In pharyngotonsillitis patients warranting extended work up for F. necrophorum, no difference in Ct-values between patients who did or did not develop complications was found. Most patients with pharyngotonsillitis had lower Ct-values than previously described in asymptomatic individuals, however factors such as degree of inflammation of tonsils, sampling technique and symptom duration were not accounted for.