Retrospective analysis of outcomes of outpatient parenteral antimicrobial therapy (OPAT) for necrotising otitis externa.

Necrotising otitis externa (NOE) is an uncommon but life-threatening infection that requires prolonged systemic antimicrobial therapy. This study aims to identify factors associated with treatment response and outcome in patients with NOE treated through outpatient parenteral antimicrobial therapy (OPAT). We performed a retrospective analysis of patients with NOE treated over a 4-year period (January 2018-January 2022) at a tertiary referral hospital in Derbyshire, UK. We defined OPAT failure as unplanned readmission within 30 days of discontinuation of OPAT. Prolonged duration of therapy was defined as length of parenteral antimicrobial treatment of more than 8 weeks. A total of 46 cases of NOE were reviewed. OPAT failure and prolonged therapy were recorded in 9 (19.6%) and 23 (50.0%) episodes respectively. Facial nerve involvement (odds ratio [OR], 14.54; 95% confidence interval [CI], 2.76-76.60; p = 0.002), dementia (OR, 7.65; 95% CI, 1.23-47.46; p = 0.029), Charlson comorbidity score (OR, 1.41 per unit increase; 95% CI, 1.00-2.00; p = 0.049) and peak CRP level (OR, 1.03 per unit increase; 95% CI, 1.00-1.06; p = 0.027) were associated with increased risk of treatment failure. Facial nerve involvement (OR, 16.30; 95% CI, 2.60-102.31; p = 0.003) and peak CRP level (OR, 1.04; 95% CI, 1.01-1.07; p = 0.016) were also associated with an increased need for prolonged antimicrobial therapy. In addition, extent of disease (based on imaging findings) was linked to prolonged therapy (OR, 22.89; 95% CI, 3.62-144.76; p = 0.001). NOE could be effectively managed as outpatient via OPAT. However, vigorous antimicrobial treatment and close monitoring of patients with pre-existing comorbidities, facial nerve paralysis, extensive disease and markedly elevated inflammatory markers are essential to optimise clinical outcomes.