Clinical implications and characterization of Group A Streptoccoccus infections in adults with cystic fibrosis.

Kate Skolnik,Barbara Waddell,Austin Nguyen,Harvey R Rabin,Ranjani Somayaji,Christina S Thornton,Michael D Parkins,Michael G Surette

doi:10.1186/s12890-015-0157-1

Kate Skolnik, Barbara Waddell + Show 6 more

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https://doi.org/10.1186/s12890-015-0157-1

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Abstract

BackgroundPersistent airway infection is a hallmark feature of cystic fibrosis (CF). However, increasingly it has been observed that non-classical pathogens may transiently infect CF lower airways. Streptococcus pyogenes (Group A Streptococcus; (GAS)) is an uncommon but potentially dangerous cause of community-acquired pneumonia. Our aim was to determine the incidence, natural history, and clinical impact of GAS infections in CF and phenotypically and genotypically characterize the isolates.MethodsWe retrospectively evaluated the Calgary Adult CF Clinic biobank to identify adults with at least one GAS isolate. Patient demographics, medical and pulmonary exacerbation (PEx) histories were evaluated. The primary outcome was PEx occurrence at incident GAS culture. Secondary outcomes evaluated were changes in lung function and PEx frequency following GAS isolation. Isolates were assessed for extra-cellular virulence factor production capacity and ability to produce quorum sensing (AI-2). Isolates were genotyped using pulse-field gel electrophoresis (PFGE).ResultsFifteen individuals who cultured GAS twenty times were identified. At the time of GAS isolation, 47 % (7/15) of subjects experienced a PEx and half of these (4/7) were severe. Individuals were more likely to have a PEx at the time of the index GAS isolate compared to the preceding visit (RR = 6.0, 95 % CI 0.82–43.0, p = 0.08), particularly if GAS was the numerically dominant sputum pathogen (RR = 6.5, 95 % CI 1.00–43.0, p = 0.009). There were no changes in PEx frequency or rate of lung function decline following GAS. None of the patients developed chronic airways infection, bacteremia, necrotizing pneumonia or empyema. Susceptibility was universal to common anti-Streptococcal antibiotics and anti-Pseudomonal antibiotics commonly used in CF, with the exception of azithromycin. GAS isolates varied in their production of protease, DNase, and AI-2 but these did not correlate with PEx, and none produced elastase, chrondrotin sulfatase or H202. One patient had prolonged carriage with the same isolate and two patients had isolates with similar PFGE patterns.ConclusionsGAS was an uncommon lower respiratory pathogen of adults with CF. Identification of GAS in sputum was frequently associated with PEx, particularly when numerically dominant. However, transient GAS infection did not result in chronic infection nor appreciably change long-term disease trajectory.

Highlights

Persistent airway infection is a hallmark feature of cystic fibrosis (CF)
Traditional perceptions focused on chronic colonization with classical CF pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae, and Burkholderia cepacia complex [6]
Population We retrospectively evaluated the Calgary Adult CF Clinic Biobank (CACFB; a prospectively collected and inventoried repository of every bacterial isolate from every CF sputum sample collected from each clinical encounter since 1978)

Summary

Introduction

Persistent airway infection is a hallmark feature of cystic fibrosis (CF). increasingly it has been observed that non-classical pathogens may transiently infect CF lower airways. CF lungs are classically characterized by viscous secretions as well as impaired mucociliary clearance [4, 5] These factors compromise airway clearance creating an optimal environment for bacterial colonization, inflammation, chronic infection, and eventually, bronchiectasis. Traditional perceptions focused on chronic colonization with classical CF pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae, and Burkholderia cepacia complex [6] Other microorganisms such as Stenotrophomonas maltophilia, Achromobacter species, and mycobacteria have been identified as emerging CF pathogens in the last two decades [6, 7]. It is apparent that CF airways disease may exist in both stable (classical CF pathogens) and dynamic states (non-classical pathogens whose presence in the CF airways disease is usually only temporary) How these transient infections affect CF outcomes is entirely unknown. Clinicians are posed with unique management challenges when these atypical microbes are isolated from the lower respiratory tracts of CF patients

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