Pulmonary exacerbations in cystic fibrosis with negative bacterial cultures

Pulmonary exacerbations are a major cause of morbidity in cystic fibrosis (CF) and likely contribute to lung function decline. Exacerbations are often associated with characteristic airway bacteria [CF related bacteria (CFRB)]. However, some patients do not have CFRB detected by culture during exacerbations.

We sought to determine the proportion of airway cultures negative for CFRB during pulmonary exacerbations, and to characterize patients who were CFRB-negative versus CFRB-positive.

We performed a retrospective study of patients with CF admitted for a pulmonary exacerbation. Patients were classified as CFRB-positive or CFRB-negative based on admission airway cultures. Demographics, clinical presentation, lung function, history of chronic Pseudomonas aeruginosa infection and improvement in lung function with treatment were compared between groups.

There were 672 admissions for exacerbation involving 211 patients over 5 years. Seventeen percent were classified as CFRB-negative. Forty-one percent of bronchoalveolar lavage (BAL), 32% of throat and 10% of sputum samples were CFRB-negative. Among patients capable of expectorating sputum, the CFRB-negative group was younger, less likely to have chronic P. aeruginosa, had higher lung function and body mass index (BMI), and had a lower systemic inflammatory response on admission compared to those with CFRB-positive cultures. The two groups had similar numbers of patients with three or more signs and symptoms of a pulmonary exacerbation (88% vs. 92%). Both groups returned to baseline lung function following treatment.

A significant number of patients with CF and pulmonary exacerbation did not have typical CFRB detected by culture. Patients without CFRB still had characteristic signs and symptoms of pulmonary exacerbation and responded to treatment. Understanding the causes of illness in these patients may improve the diagnosis and treatment of pulmonary exacerbations in CF.