Our previous research has suggested that ‘respiratory exacerbations’ in patients with antibody deficiency are more often positive for pathogenic viruses than bacteria.5 Patients self-treated for presumed bacterial infection even with predominantly upper respiratory tract symptoms, but response to antibiotics was predicted by sputum purulence.5 We therefore investigated the relationship between neutrophil elastase and bacterial populations in sputum as a rapid tool to inform antibiotic use. Here, ELANE is linked to bacterial infectious disease.