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Group A streptococcus increases pulmonary exacerbation risk in CF patients

Patients with cystic fibrosis appeared more at risk for a pulmonary exacerbation if Group A Streptococcus was found in the sputum as the dominant organism, according to recent research.

“[Group A Streptococcus (GAS)] was an uncommon, transient lower respiratory pathogen in our population of adults with [cystic fibrosis (CF)],” Kate Skolnik, MD, of the departments of medicine at The University of Calgary in Canada, and colleagues wrote. “In our cohort, identification of GAS in sputum, particularly as the dominant organism, was associated with an increased [pulmonary exacerbation] risk. However, GAS colonization of the lower airways was transient and, as such, did not impact lung function and did not appreciably change the disease trajectory.”

Skolnik and colleagues evaluated GAS isolates in 15 patients from an adult CF biobank, according to the abstract. Researchers analyzed patients for pulmonary exacerbation history, medical history and patient demographic data as well as indications of pulmonary exacerbation at the time of GAS culture and changes in lung function and frequency of pulmonary exacerbation after isolation of GAS. The researchers used indicators of extra-cellular virulence factor production capacity and the ability to produce quorum sensing (AI-2) to identify isolates, which were genotyped using pulse-field electrophoresis.

They found 47% of patients (n = 7) had a pulmonary exacerbation during GAS isolation, with approximately half (n = 4) having severe pulmonary exacerbations during isolation, according to the abstract. All patients had GAS cultured 20 times, and patients with pulmonary exacerbations were more likely to have these events during the index culture visit compared with the preceding visit (RR = 6; 95% CI, 0.82-43; P = .08); in these cases, the risk was even higher if GAS was the dominant sputum pathogen present (RR = 6.5; 95% CI, 1-43; P = .009).

The researchers reported no complications regarding bacteremia, chronic airway infections, empyema or necrotizing pneumonia, and patients did not experience a change in lung function or rate of pulmonary exacerbation after GAS, according to the abstract.  

“Importantly, our GAS strains were sensitive to antibiotics commonly used in the empiric treatment of CF [pulmonary exacerbation], although ceftazidime, an antibiotic commonly used in the empiric [pulmonary exacerbation] management, should not be used where GAS is involved,” Skolnik and colleagues wrote. “Nearly all strains were sensitive to azithromycin; this raises the possibility that chronic azithromycin may suppress GAS and prevent initial colonization.” – by Jeff Craven

Disclosure: Skolnik reports no relevant financial disclosures. Two researchers report research grants from Cystic Fibrosis Canada and Gilead. Two researchers report advisory board roles for Gilead, Novartis, Roche and Vertex.