Post-Pandemic shifts in peritonsillar abscess: incidence and microbiological trends following the cessation of COVID-19-related nonpharmaceutical interventions.

Background: The impact of COVID-19-related nonpharmaceutical interventions (NPI) on the bacterial composition of upper airway infections remains largely unexplored.

Objectives: We aimed to investigate the incidence and microbiology of peritonsillar abscess (PTA) following the cessation of NPI and to compare these findings with the periods before and during NPI implementation.

Methods: We performed a cross-sectional analysis of all PTA cases and their microbiological findings from 12 March, 2018 to 11 March, 2024, among patients admitted to the Ear-Nose-Throat Department, Aarhus University Hospital. Patients were categorised into three two-year periods in relation to NPI. Age-stratified population data for the catchment area were sourced from Statistics Denmark.

Results: A total of 1,030 patients were included. The annual incidence rate of PTA was significantly higher post-NPI (26.9 cases/100,000) compared to both the NPI period (14.9 cases/100,000, p < 0.001) and the pre-NPI period (21.8 cases/100,000, p = 0.003). Increased post-NPI rates were observed across all age groups. The number of cases positive for Streptococcuspyogenes and Fusobacterium necrophorum increased post-NPI (n = 102 and n = 89, respectively) compared to during the NPI period (n = 28 and n = 64, p < 0.001 and p = 0.052, respectively) and pre-NPI (n = 67 and n = 60, p = 0.009 and p = 0.021, respectively). Statistically non-significant increasing trends were found for less prevalent bacteria.

Conclusion: Following NPI cessation, PTA incidence rates surpassed both the NPI and pre-NPI levels. The rising PTA incidence rates post-NPI were primarily driven by an increasing number of cases positive for S. pyogenes and F. necrophorum, suggesting an immunity debt to these prevalent pathogens.