Sustained Coinfections with Staphylococcus aureus and Pseudomonas aeruginosa in Cystic Fibrosis.

Rationale : Staphylococcus aureus and Pseudomonas aeruginosa often infect the airways in cystic fibrosis (CF). Because registry studies show higher prevalence of P. aeruginosa versus S. aureus in older patients with CF, a common assumption is that P. aeruginosa replaces S. aureus over time. In vitro , P. aeruginosa can outgrow and kill S. aureus . However, it is unknown how rapidly P. aeruginosa replaces S. aureus in patients with CF. Methods : We studied a longitudinal cohort of children and adults with CF who had quantitative sputum cultures. We determined the abundance of P. aeruginosa and S. aureus in cfu/ml. We determined the duration and persistence of infections and measured longitudinal changes in culture positivity and abundance for each organism. Measurements and Main Results : Between 2004 and 2017, 134 patients had ≥10 quantitative cultures, with median observation time of 10.15 years. One hundred twenty-four patients had at least one positive culture for P. aeruginosa , and 123 had at least one positive culture for S. aureus . Both species had median abundance of >10 ⁶ cfu/ml. Culture abundance was stable over time for both organisms. There was an increase in the prevalence of S. aureus / P. aeruginosa coinfection but no decrease in S. aureus prevalence within individuals over time. Conclusions : S. aureus and P. aeruginosa are abundant in CF sputum cultures. Contrary to common assumption, we found no pattern of replacement of S. aureus by P. aeruginosa . Many patients with CF have durable long-term coinfection with these organisms. New strategies are needed to prevent and treat these infections.