Throat Swabs and Sputum Culture as Predictors of P. aeruginosa or S. aureus Lung Colonization in Adult Cystic Fibrosis Patients

Abstract

BackgroundDue to frequent infections in cystic fibrosis (CF) patients, repeated respiratory cultures are obtained to inform treatment. When patients are unable to expectorate sputum, clinicians obtain throat swabs as a surrogate for lower respiratory cultures. There is no clear data in adult subjects demonstrating the adequacy of throat swabs as a surrogate for sputum or BAL. Our study was designed to determine the utility of throat swabs in identifying lung colonization with common organisms in adults with CF.MethodsAdult CF subjects (n = 20) underwent bronchoscopy with BAL. Prior to bronchoscopy, a throat swab was obtained. A sputum sample was obtained from subjects who were able to spontaneously expectorate. All samples were sent for standard microbiology culture.ResultsUsing BAL as the gold standard, we found the positive predictive value for Pseudomonas aeruginosa to be 100% in both sputum and throat swab compared to BAL. However, the negative predictive value for P. aeruginosa was 60% and 50% in sputum and throat swab, respectively. Conversely, the positive predictive value for Staphylococcus aureus was 57% in sputum and only 41% in throat swab and the negative predictive value of S. aureus was 100% in sputum and throat swab compared to BAL.ConclusionsOur data show that positive sputum and throat culture findings of P. aeruginosa reflect results found on BAL fluid analysis, suggesting these are reasonable surrogates to determine lung colonization with P. aeruginosa. However, sputum and throat culture findings of S. aureus do not appear to reflect S. aureus colonization of the lung.

Volatile molecules from bronchoalveolar lavage fluid can ‘rule-in’ Pseudomonas aeruginosa and ‘rule-out’ Staphylococcus aureus infections in cystic fibrosis patients

“…Seidler et al . reported that in expectorating adults (n = 20), OP swab and sputum cultures both had a PPV of 1.00 for detecting P. aeruginosa and NPV of 0.50 and 0.60, respectively 39 . In this work, 28 putative volatile biomarkers were selected across all our models for the identification of P. aeruginosa in BAL fluid samples yielding a PPV range of 0.25–0.81 and an NPV range of 0.56–0.92.…”

“…Seidler et al . reported an NPV of 1.00 for detecting S. aureus in OP swab and sputum cultures versus BAL fluid and a PPV of 0.41 for OP swab and 0.57 for sputum versus BAL fluid 39 . Neericnx et al .…”

Help, hinder, hide and harm: what can we learn from the interactions betweenPseudomonas aeruginosaandStaphylococcus aureusduring respiratory infections?

“…Properly defining coinfection may also be influenced by the sampling methods used, particularly in young children, who often do not expectorate. Some studies indicate that both sputum and oropharyngeal swab cultures can, in some contexts and for specific organisms, reflect lower airway microbiology identified by bronchoalveolar lavage (BAL)45 or direct sampling of mucous plugs by protected brush (PB) sampling,46 while other studies found poor such correlations. For example, Seidler and colleagues found that while the positive predictive value of both sputum and throat swabs for identifying P. aeruginosa was 100%, in comparison with BAL, the positive predictive values of these two sample types for S. aureus were only 57% and 41%, respectively 45.…”

Pseudomonas pharyngitis in a cystic fibrosis patient

“…There are several studies looking at routine throat swabs for the isolation of pathogens in CF mainly in the paediatric populations. A recent study looked at throat swabs as a marker of lower‐airway Pseudomonas colonization . This study showed that both sputum and throat swab were 100% sensitive in predicting BAL Pseudomonas, whereas the negative predictive value of a throat swab was only 50%.…”