Palivizumab prophylaxis in infants with cystic fibrosis does not delay first isolation of Pseudomonas aeruginosa or Staphylococcus aureus.

Respiratory syncytial virus (RSV) infections may worsen cystic fibrosis (CF) lung disease and favor Pseudomonas aeruginosa (Pa) or Staphylococcus aureus (Sa) acquisition, which is of particular importance in the youngest patients. We aimed to determine the effectiveness of PVZ on microbiological outcomes in young children with CF. We conducted a retrospective case-control study to compare these outcomes in children who systematically received PVZ (PVZ+; n = 40) or not (PVZ-; n = 140). One case was matched with at least three same-gender controls born the same year and month. Median (range) age at first Pa isolation was not statistically different between PVZ- (12.3 [3.8-32.6] months) and PVZ+ (10.4 [1.2-33.0] months; p = 0.953) patients. A similar trend was found for Sa (PVZ+: 6.4 [2.0-59.0] months; PVZ-: 3.8 [0.1-74.1] months; p = 0.191). The proportion of Pa isolations by 3 years of age did not differ between groups (PVZ+ 40% vs. PVZ- 41.4%), but this proportion was higher for Sa in the PVZ+ group (97%) than in the PVZ- group (85%; p = 0.001). Healthcare consumption and growth outcomes did not significantly differ between groups. CONCLUSION: Systematic PVZ use did not delay key pathogen acquisition in young children with CF. What is known: • Palivizumab is the only available monoclonal antibody against respiratory syncytial virus infection. • Whether or not it is useful in infants with cystic fibrosis remains controversial. What is new: • Palivizumab does not delay key pathogens (Pseudomonas aeruginosa, Staphylococcus aureus) first isolation in young children with cystic fibrosis. • Palivizumab does not reduce healthcare consumption or improve growth during the first 3 years of life of young children with cystic fibrosis.