Low Eosinophils Linked to Sputum Bacteria in Bronchiectasis

Key Takeaways

• In a single-center cohort of people with bronchiectasis without asthma or chronic obstructive pulmonary disease, eosinopenia coincided with more frequent positive stable-state sputum cultures than intermediate eosinophil counts.
• Pseudomonas aeruginosa isolation and neutrophil-to-lymphocyte ratio were higher with eosinopenia than with intermediate counts.
• Neither eosinophil extreme had a statistically significant adjusted association with later bronchiectasis exacerbation.
• Hospitalization was numerically more frequent with eosinophilia, but the overall difference among the groups was not statistically significant.

Even during clinical stability, people with bronchiectasis can have different airway microbiology and inflammatory profiles. Investigators retrospectively assessed patients at one Ankara institution in a study published inMedicina. Of those assessed, 163 patients with bronchiectasis were eligible after exclusions including asthma and chronic obstructive pulmonary disease. Diagnosis required respiratory symptoms and history alongside diagnostic high-resolution computed tomography (HRCT). The first HRCT defined the index date; a blood eosinophil count obtained that day assigned patients to eosinopenia (≤100 cells/µL), intermediate counts (101–299 cells/µL), or eosinophilia (≥300 cells/µL). Clinical stability required no recent documented exacerbation, acute respiratory emergency visit or hospitalization, or systemic corticosteroid use. Cultures obtained during acute illness or antibiotic treatment were excluded. Investigators assessed subsequent clinical events over a year and adjusted the exacerbation analysis for age, sex, modified Reiff score, and eosinophil category.

Positive stable-state sputum cultures occurred in 53.1% of patients with eosinopenia versus 21.3% with intermediate eosinophil counts, a significant Bonferroni-adjusted pairwise difference. This finding describes bacterial isolation at sampling, not the ability of eosinophil counts to predict later events. The eosinopenic group also had a higher neutrophil-to-lymphocyte ratio (NLR), consistent with a different systemic inflammatory profile.

Stable-state Pseudomonas aeruginosa isolation was also significantly more frequent with eosinopenia than with intermediate counts; lymphocyte counts were lower in the eosinopenic group. Neither eosinophil extreme was significantly associated with subsequent exacerbation after adjustment, and eosinophil count showed limited discrimination for that outcome. Hospitalization was numerically more frequent with eosinophilia, but the overall comparison among the three groups was not significant and did not establish a pairwise effect.

The investigators interpreted the microbiological and inflammatory differences as potential bronchiectasis phenotypes rather than evidence of a linear exacerbation predictor. The retrospective, single-center Ankara cohort relied on one stable-state eosinophil measurement; lung-function and etiologic information, pre-index exacerbation history, and some maintenance treatment data were incomplete. Without serial sputum cultures or per-patient sampling frequency, P. aeruginosa detection represents isolation, not established chronic infection or colonization. The exacerbation model did not adjust for smoking, culture positivity, or NLR, and missing values were not imputed. These associations do not establish causation, validate individual risk prediction or eosinophil-guided treatment, or prove that exacerbation risk is unaffected.

The authors concluded that blood eosinophil counts may distinguish bronchiectasis phenotypes, while their prognostic significance and stability over time warrant prospective evaluation with repeated measurements.

Clinician Questions

How was a bronchiectasis exacerbation defined when evaluating blood eosinophil phenotypes?

Among patients grouped by stable-state blood eosinophils, investigators counted an exacerbation when symptoms worsened for more than 48 hours in at least three categories—cough, sputum volume or consistency, sputum purulence, breathlessness or exercise tolerance, fatigue or malaise, or hemoptysis—and treatment changed.

Did inhaled corticosteroid use differ across eosinophil categories in bronchiectasis?

Among patients grouped by stable-state blood eosinophil counts, recorded maintenance use of inhaled corticosteroids did not differ significantly across the groups. This comparison assessed treatment exposure, not corticosteroid response or eosinophil-guided prescribing.