Multi-year Population-Based Study of the Clinical and Epidemiological Risk Factors for Mortality in Nocardiosis: Survival Analysis from a Large Regional Canadian Healthcare Region

BACKGROUND Nocardiae are ubiquitous environmental soil pathogens that primarily cause invasive infections by inhalation or direct skin inoculation in immunocompromised patients. This multi-year population-based study compared epidemiological and clinical features of all cases diagnosed in our region. METHODS Patients were enrolled in our large integrated healthcare region with culture-proven nocardiosis between 2010–2022. Clinical chart reviews were conducted to determine the clinical manifestations, risk factors, treatment and mortality including survival analysis. RESULTS Ninety-four adults had a mean age of 61 ± 17 yrs. More cases occurred in males (57%) than females (43%). Ninety-six percent of cases had underlying co-morbidities including diabetes, liver or renal failure, malignancy, transplant recipients, chronic lung disease, rheumatologic disease, or other inflammatory conditions. Pulmonary (53%) or skin and soft tissue infections (SSTIs) (30%) commonly occurred with infrequent diagnoses of central nervous system infection (CNS) (7%), bloodstream infection (BSI) (6%), and septic arthritis or intra-abdominal infection (IAI) (6%). Diverse Nocardia spp. were isolated, but 3 species complexes caused most cases [56/94 (60%)] including Nocardia farcinica (n = 21, 22.3%), Nocardia cyriacigeorgica (n = 16, 17%) and Nocardia nova (n = 19, 20.2%). Clinical presentation was not unique for individual Nocardia spp. infections. Overall mortality was 22.3% with a 1-year mortality of 12.2%. Delayed diagnosis (≥ 30 d) from symptom onset had higher mortality. Increased mortality occurred for N. nova  >  N. cyriacigeorgica  >  N. farcinica complex infections. CONCLUSIONS Prompt diagnosis of nocardiosis improves patient outcomes. Nocardia species-level identification predicts mortality for major species complexes causing nocardiosis in our region.