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Disease severity in siblings with cystic fibrosis
Sherri L Katz1, Lisa J Strug, Allan L Coates
1Division of Respiratory Medicine, Hospital for Sick Children, Toronto, Ontario, Canada.
Insights
Subsequent siblings with cystic fibrosis (CF) do not appear to acquire respiratory pathogens earlier or experience more severe lung disease. Initial findings of earlier pathogen acquisition in younger siblings were likely due to diagnosis bias in older siblings.
Area of Science:
- Pulmonology
- Infectious Diseases
- Genetics
Background:
- Cross-infection between siblings with cystic fibrosis (CF) is a known concern.
- The potential impact of sibling infection on the age of pathogen acquisition and disease severity in subsequent children with CF requires investigation.
Purpose of the Study:
- To investigate if younger siblings of children with CF acquire respiratory pathogens (Pseudomonas aeruginosa, Staphylococcus aureus) at an earlier age.
- To determine if younger siblings experience a more severe course of pulmonary disease compared to their older siblings.
Main Methods:
- Retrospective cohort study of 31 sibling pairs diagnosed with CF.
- Kaplan-Meier curves and modified log-rank tests analyzed age of pathogen acquisition.
- Clinical parameters including hospitalization rates, antibiotic courses, and lung function (FEV1) were compared.
Main Results:
- Older siblings were diagnosed with Staphylococcus aureus and other CF pathogens at a later age than younger siblings.
- However, a higher proportion of older siblings were culture-positive at initial diagnosis, suggesting an age-of-diagnosis bias.
- No significant differences were observed in hospitalization rates, oral antibiotic courses, FEV1 % predicted, or growth parameters between older and younger siblings.
Conclusions:
- The observed earlier isolation of pathogens in younger siblings is likely an artifact of diagnosis bias in older siblings.
- There is no evidence to suggest that younger siblings with CF acquire pathogens earlier or have worse clinical outcomes compared to their older siblings.
Abstract:
Since cross-infection occurs between cystic fibrosis (CF) siblings, we hypothesized that subsequent siblings may acquire respiratory pathogens at an earlier age and have a more severe course of pulmonary disease. We studied a retrospective cohort of 31 sibling pairs from the CF database at the Hospital for Sick Children. Kaplan-Meier curves and modified log-rank tests were used to test sibling differences in age of acquisition of Pseudomonas aeruginosa (PA), Staphylococcus aureus (SA), or any positive culture. Differences in disease severity outcomes were explored. Older siblings were more likely to have both SA and any CF pathogen first isolated from respiratory culture at an older age than younger siblings (P = 0.0050 and P = 0.0008, respectively, by modified log-rank tests). However, more of the older siblings were positive on first culture at time of diagnosis, introducing an age-of-diagnosis bias. Hospitalization rates, courses of oral antibiotics, FEV(1) % predicted, and weight and height measurements were not better in the older children. No differences in clinical parameters were found between older and younger siblings. The apparent finding of younger age at first isolation of pathogens from respiratory cultures in younger siblings is likely because many older siblings were already infected with these organisms at time of diagnosis.
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