# Association between clinical outcome and microbiological findings in peritonsillar abscess - an observational study

## TL;DR

This study finds that Fusobacterium necrophorum is the most common cause of peritonsillar abscesses and is linked to more complications in patients.

## Contribution

The study identifies F. necrophorum as the most frequent pathogen and the only one associated with complications in peritonsillar abscesses.

## Key findings

- Fusobacterium necrophorum was detected in 33% of patients with peritonsillar abscesses.
- F. necrophorum was associated with both early and late complications following abscess diagnosis.

## Abstract

Previous studies on causative pathogens in peritonsillar abscesses have yielded varying results. However, Group A streptococci (GAS) and Fusobacterium necrophorum have been identified frequently. The aim of this study was to investigate pathogens in peritonsillar abscesses in patients tested for both ß-hemolytic streptococci and F. necrophorum, and to investigate associations between pathogens and clinical outcome.

This retrospective observational study included all patients in the Skåne Region, Sweden (population 1.4 million) with a diagnosis of peritonsillar abscess between 2016 and 20, and in whom tests were performed for both ß-hemolytic streptococci (culture) and F. necrophorum (PCR). Exclusion criteria included previous (30 days) purulent complication to pharyngotonsillitis or antibiotic therapy. Chart review from 30 days prior to 6 months after the index visit was performed. Logistic regression was performed to evaluate the association between pathogens and complications, with negative microbiological findings set as reference category. Complications were defined as a composite outcome (0/1) of recurrent pharyngotonsillitis/peritonsillar abscess, other pharyngeal abscess or septic complications within 30 days (early), and 1–6 months (late).

In a total of 637 patients, F. necrophorum was identified in 210 (33%), GAS in 159 (28%) and GCS/GGS in 40 (6%) patients. F. necrophorum was most common in adolescents and young adults. Only F. necrophorum was associated with the development of either of early (OR 3.8 (2.0-7.1 95%CI)) and late complications (OR 2.5 (95%CI 1.3–4.9).

F. necrophorum was the most commonly identified pathogen in peritonsillar abscesses. It was also the only pathogen associated with the development of complications.

The online version contains supplementary material available at 10.1007/s10096-025-05156-y.