Associations Between Findings of Fusobacterium necrophorum or β-Hemolytic Streptococci and Complications in Pharyngotonsillitis—A Registry-Based Study in Southern Sweden

BACKGROUND: Most pharyngotonsillitis guidelines focus on the identification of group A streptococci (GAS), guided by clinical scores determining whom to test with a rapid antigen detection test. Nevertheless, many patients testing negative with this test are evaluated for group C/G streptococci (GCS/GGS) and Fusobacterium necrophorum, yet their importance remains debated. Our primary aim was to evaluate associations between complications and findings of F. necrophorum, GAS, or GCS/GGS in pharyngotonsillitis. METHODS: This was a retrospective, registry-based study of pharyngotonsillitis cases tested for F. necrophorum (polymerase chain reaction) and β-hemolytic streptococci (culture) in the Skåne Region, Sweden, in 2013–2020. Patients with prior complications or antibiotics (within 30 days) were excluded. Data were retrieved from registries and electronic charts. Logistic regression analyses were performed with a dichotomous composite outcome of complications as primary outcome, based on International Classification of Diseases, Tenth Revision, codes. Cases with negative results (polymerase chain reaction and culture) were set as reference category. Complications within 30 days were defined as peritonsillar or pharyngeal abscess, otitis, sinusitis, sepsis or septic complications, recurrence of pharyngotonsillitis (after 15–30 days) or hospitalization. RESULTS: Of 3700 registered cases, 28% had F. necrophorum, 13% had GCS/GGS, 10% had GAS, and 54% had negative results. The 30-day complication rates were high (20%). F. necrophorum (odds ratio, 1.8; 95% confidence interval, 1.5–2.1) and GAS (1.9; 1.5–2.5) were positively associated with complications, whereas GCS/GGS were negatively associated (0.7; 0.4–0.98). CONCLUSIONS: Our results indicate that F. necrophorum is a relevant pathogen in pharyngotonsillitis, whereas the relevance of testing for GCS/GGS is questioned. However, which patient to test and treat for F. necrophorum remains to be defined.