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Bacterial reservoirs in cystic fibrosis
C J Taylor1, J McGaw, R Howden
1Department of Paediatrics, University of Sheffield.
Insights
In cystic fibrosis patients, upper airway Pseudomonas aeruginosa colonization does not predict lower airway infection. Inhaler devices showed no contamination, and upper airway bacteria poorly correlated with sputum isolates.
Area of Science:
- Medical Microbiology
- Pulmonology
- Pediatrics
Background:
- Cystic fibrosis (CF) patients are susceptible to chronic respiratory infections.
- Pseudomonas aeruginosa (P. aeruginosa) is a key pathogen in CF lung disease.
- The source of P. aeruginosa colonization in CF airways remains debated.
Purpose of the Study:
- To investigate if upper respiratory tract colonization or inhaler contamination predisposes CF patients to lower airway P. aeruginosa colonization.
- To determine the relationship between upper airway bacterial carriage and lower respiratory tract isolates in children with CF.
Main Methods:
- Bacterial isolates from upper airways, inhaler devices, and toothbrushes were compared with sputum/cough swab cultures.
- Children with CF were grouped based on P. aeruginosa sputum culture results (positive or negative).
- Isolates of Staphylococcus aureus, Haemophilus influenzae, and P. aeruginosa were analyzed.
Main Results:
- No P. aeruginosa was detected in inhaler devices used for unit-dose medications.
- Upper airway Staphylococcus aureus and Haemophilus influenzae were common but poorly correlated with sputum isolates.
- P. aeruginosa was exclusively found in the upper airways of children with established lower airway colonization.
- No P. aeruginosa was isolated from the upper airways of children without lower airway P. aeruginosa, even if they later became colonized.
Conclusions:
- Upper respiratory tract colonization by P. aeruginosa does not appear to predispose to lower airway colonization in CF patients.
- Inhaler contamination is unlikely to be a significant source of P. aeruginosa in CF.
- Consistent isolation of pathogens from the upper airways is not a reliable predictor of lower airway colonization in CF, challenging the role of local epithelial factors.
Abstract:
To establish whether colonisation of the upper respiratory tract or bacterial contamination of inhaler devices or solutions predisposes to colonisation of the lower respiratory tract in patients with cystic fibrosis, bacterial isolates from groups of children who were positive (n = 13) or negative (n = 18) for Pseudomonas aeruginosa were studied. Cultures of swabs from inhaler devices, toothbrushes, and upper airways were compared with cough swabs or sputum cultures. No pathogens were obtained from inhaler equipment administering unit dose medications. Upper airway carriage of Staphylococcus aureus and Haemophilus influenzae was identified in both groups but correlated poorly with sputum isolates. P. aeruginosa was found only in the upper respiratory tract of children with established colonisation of the lower airways. No P aeruginosa isolates were obtained from the upper airways of the group with negative sputum, including one patient who became colonised by P aeruginosa during the study. Our results did not support the suggestion that colonisation of the upper respiratory tract by P aeruginosa predisposes to colonisation of the lower airways. Failure to isolate pathogenic organisms consistently from the upper airways in patients with positive sputum argues against a local epithelial factor predisposing to bacterial colonisation.