# P-609. Epidemiology and Outcomes of Nocardia Colonization

## TL;DR

This study compares Nocardia colonization with active nocardiosis, identifying risk factors and outcomes to better understand disease progression.

## Contribution

The study provides new insights into distinguishing Nocardia colonization from active disease and identifies risk factors for progression.

## Key findings

- Immunocompetent patients with chronic lung disease are more likely to have Nocardia colonization.
- Lung cavitation is associated with pulmonary nocardiosis rather than colonization.
- Colonized patients had a lower one-year mortality rate compared to those with active disease, though not statistically significant.

## Abstract

Nocardia species are known to cause both respiratory colonization and pulmonary nocardiosis, with the latter leading to significant morbidity and mortality. There is limited data showing a distinction between colonization and active disease, as well as disease progression and optimal management strategies. This study compares individuals with respiratory Nocardia colonization to those diagnosed with pulmonary nocardiosis, with a focus on baseline characteristics, survival outcomes, and risk factors associated with disease progression.Table 1.Cohort CharacteristicsEpidemiology and Outcomes of Nocardia Colonization

Cohort Characteristics

Epidemiology and Outcomes of Nocardia Colonization

We analyzed 225 patients with Nocardia species isolated in respiratory cultures from 2000 to 2023 at a tertiary hospital in Cleveland, Ohio. Nocardiosis was defined as Nocardia growth in culture with accompanying signs, symptoms, and radiologic findings consistent with active infection. Nocardia colonization was the isolation of Nocardia on cultures without clinical disease. We conducted a retrospective cohort study comparing two groups: individuals with respiratory Nocardia colonization and those with pulmonary nocardiosis. Factors associated with colonization were assessed by multivariable logistic regression.

Fifty-five (24.4%) patients with Nocardia colonization and 170 patients (75.6%) with nocardiosis were included (Table 1). Immunocompetent patients with chronic lung disease (adjusted OR 7.73, CI 3.37-19.95, p≤0.001) and patients with a higher Charlson comorbidity index (OR 1.52 per point, 95% CI 1.27-1.85, p≤0.001) had an increased likelihood of Nocardia colonization. Lung cavitation was associated with nocardiosis (adjusted OR 0.21, 95% CI 0.05-0.68, p=0.020), while identification of N. farcinica was not statistically significant (adjusted OR 0.28, 95% CI 0.04-1.05, p=0.102). Patients with colonization had a lower, though non-significant one-year mortality rate (7.3% versus 17.1%, log-rank p=0.061).

These findings delineate important differences in patient characteristics and survival outcomes between respiratory Nocardia colonization and pulmonary nocardiosis, highlighting the need for prospective studies to identify colonized patients who are at risk for disease progression.

Susan Harrington, PhD, Bruker Daltonics, Inc: Grant/Research Support