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Background: Acute tonsillitis and peritonsillar abscess (PTA) are common infections in primary care and otorhinolaryngology. Uncertainties remain regarding microbial aetiology, optimal diagnosis, and treatment. This thesis clarifies the roles of key bacterial pathogens, evaluates diagnostic methods, and supports evidence-based clinical decision-making. 

Materials & Methods: Three studies were conducted. Study I included healthy individuals; Study II included patients with tonsillitis or PTA. Tonsillar swabs and peritonsillar pus were analysed by culture and PCR for Streptococcus pyogenes (GAS), Streptococcus dysgalactiae subspecies equisimilis (SDSE), Fusobacterium necrophorum (FN), and Arcanobacterium haemolyticum (AH). Serum CRP and calprotectin were measured to assess inflammatory response and diagnostic performance. Study III included PTA patients and retrospectively examined risk factors for recurrence and tonsillectomy outcomes. 

Results: Project I included 217 healthy adolescents and young adults (16–25 years). Tonsillar swabs showed 25 % carried one or more target species: GAS and FN were each present in 10% of individuals, SDSE in 8 %, and AH in 1 %. GAS and FN had significantly higher detection by PCR than culture, mainly due to individuals where semi-quantitative PCR indicated a low bacterial load in the initial samples.

Project II included 113 acute-tonsillitis patients (Centor score 3–4) and 70 PTA patients. Culture and PCR had similar detection for all targets except AH, detected more often by PCR in tonsillitis. 

Tonsillitis patients had a target bacterial species in 79 % of cases: GAS 63 %, FN 12 %, SDSE 7 %, AH 7 %. Patients with GAS had higher CRP and calprotectin levels than patients with other bacteria, or no bacteria.

In PTA, GAS occurred in 35 %, FN 22 %, SDSE 6 %, AH 2 %. PTA patients with FN had significantly higher CRP and calprotectin than others.

Project III included 292 consecutive PTA patients, of whom 18 underwent immediate, quinsy tonsillectomy. Of the remaining 274 who underwent pus drainage by aspiration or incision, 19 % experienced a recurrence. Cox regression identified young age as a risk factor for recurrence, while sex and a previous history of PTA were not significant. Among the youngest patients (15–24 years), PTA recurred in 28 %, most often within 30 days, and 47 % of them underwent tonsillectomy during the study period (for any indication). Older patients (>30 years) had few recurrences (4 %) and few tonsillectomies (15 %). Tonsillectomy effectively eliminated recurrence, as none of the 101 operated patients experienced PTA recurrence after surgery.

Conclusion: Asymptomatic carriage of GAS, SDSE, and FN is common among adolescents and young adults. GAS predominated in tonsillitis, while other pharyngeal bacterial pathogens were detected at low rates. CRP and calprotectin increase in GAS tonsillitis but add no diagnostic value. GAS and FN predominated in PTA, with the highest inflammatory biomarker levels observed in FN cases. The risk of PTA recurrence is strongly age-dependent; early tonsillectomy should be considered in the youngest patients.

Background: Peritonsillar abscess (PTA) can be treated with aspiration or incision for drainage, but a subsequent PTA can occur if tonsillectomy is not performed. Better understanding is needed of when tonsillectomy should be performed to avoid PTA recurrence.

Objective: This study investigated the recurrence rate of PTA following aspiration or incision for drainage and evaluated the risk factors for recurrence.

Methods: The medical records of 292 patients treated for PTA were reviewed. Recurrence of PTA and elective or quinsy tonsillectomy were the primary endpoints. A Cox proportional hazards regression model for PTA recurrence was constructed with sex, age, and PTA history as predictors.

Results: Young age was the only significant predictor of PTA recurrence. Patients aged 15 to 24 years had a 30-day recurrence rate of 15.5% and a total recurrence rate of 26.6%. The total recurrence rate among patients over 30 years of age was significantly less at 4.0% (Fisher’s exact test, p <.05).

Conclusion and Significance: Based on our results, tonsillectomy should be considered for PTA in patients between 15 and– 25 years of age and, to effectively avoid future recurrence of PTA, should be performed urgently.

The pharyngeal mucosa can be colonized with bacteria that have potential to cause pharyngotonsillitis. By the use of culturing techniques and PCR, we aimed to assess the prevalence of bacterial pharyngeal pathogens among healthy adolescents and young adults. We performed a cross-sectional study in a community-based cohort of 217 healthy individuals between 16 and 25 years of age. Samples were analyzed for Group A streptococci (GAS), Group C/G streptococci (SDSE), Fusobacterium necrophorum, and Arcanobacterium haemolyticum. Compared to culturing, the PCR method resulted in more frequent detection, albeit in most cases with low levels of DNA, of GAS (20/217 vs. 5/217; p < 0.01) and F. necrophorum (20/217 vs. 8/217; p < 0.01). Culturing and PCR yielded similar rates of SDSE detection (14/217 vs. 12/217; p = 0.73). Arcanobacterium haemolyticum was rarely detected (3/217), and only by PCR. Overall, in 25.3% (55/217) of these healthy adolescents and young adults at least one of these pathogens was detected, a rate that is higher than previously described. Further studies are needed before clinical adoption of PCR-based detection methods for pharyngeal bacterial pathogens, as our findings suggest a high incidence of asymptomatic carriage among adolescents and young adults without throat infections.