A UK multi-centre prospective observational study of clinically possible cases of NOE.

Patients with clinically possible NOE for whom CT imaging is requested will be recruited to the study by hospital staff at 20-25 UK sites.

NOE remains a relatively uncommon condition with UK - ENT surgeons report seeing between 1 and 10 cases per year. We plan to recruit 350 patients consented prior to or after CT imaging for a diagnosis of clinically possible NOE. After providing consent, patients will be asked to complete an EQ-5D-3L questionnaire. For patients consented remotely, this questionnaire will be completed via an interview. Local study staff will complete an online case report form hosted on Redcap™ for each patient including data on demographics, co-morbidities, clinical presentation, investigations and surgical and antibiotic management. Local study staff will review patients' hospital notes and contact patients' GPs by telephone 1-year post recruitment to assess clinical outcomes and mortality rates. Patients will then be contacted 12 months (+/- 1 month) post-recruitment by telephone by local study staff in order to confirm clinical outcomes (e.g. relapse) and gain information to complete the EQ-5D-3L questionnaire a second time.

All CT scans performed at recruitment and any other CT and/or MRI scans performed in the 12-month follow-up period will be de-identified and uploaded by local sites to an online, web-based secure repository for radiological images. Subspecialised radiologists blinded to clinical details will assess the images according to pre-agreed, standardised criteria.

Selected sites will be asked to freeze any P. aeruginosa isolates routinely collected via ear swabs as part of clinical care from enrolled participants within 14 days of CT imaging. These de-identified samples may be sent from sites to undergo genotypic and phenotypic analysis at the University of Oxford for virulence factors to assess the relationship between these and disease severity. Of note, no samples beyond those routinely collected as part of the patients' care will be collected and no patient tissue samples will be stored. These samples will not contain any biological or genetic material from the patient.

Inclusion Criteria:

• Adult patients (≥ 18 years old).
• Clinical diagnosis of possible NOE for whom CT imaging is requested or has been done as part of routine clinical care.

Exclusion Criteria:

• Any previous clinical diagnosis of NOE.
• CT performed or due to be performed at hospital other than recruiting study site.

Patients will be consented prior to or after CT imaging for a diagnosis of clinically possible NOE.