Sustained Coinfections with <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i> in Cystic Fibrosis

Abstract

<b>Rationale</b>: <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i> often infect the airways in cystic fibrosis (CF). Because registry studies show higher prevalence of <i>P. aeruginosa</i> versus <i>S. aureus</i> in older patients with CF, a common assumption is that <i>P. aeruginosa</i> replaces <i>S. aureus</i> over time. <i>In vitro</i>, <i>P. aeruginosa</i> can outgrow and kill <i>S. aureus</i>. However, it is unknown how rapidly <i>P. aeruginosa</i> replaces <i>S. aureus</i> in patients with CF.<b>Methods</b>: We studied a longitudinal cohort of children and adults with CF who had quantitative sputum cultures. We determined the abundance of <i>P. aeruginosa</i> and <i>S. aureus</i> in cfu/ml. We determined the duration and persistence of infections and measured longitudinal changes in culture positivity and abundance for each organism.<b>Measurements and Main Results</b>: 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 <i>P. aeruginosa</i>, and 123 had at least one positive culture for <i>S. aureus</i>. Both species had median abundance of >10⁶ cfu/ml. Culture abundance was stable over time for both organisms. There was an increase in the prevalence of <i>S. aureus</i>/<i>P. aeruginosa</i> coinfection but no decrease in <i>S. aureus</i> prevalence within individuals over time.<b>Conclusions</b>: <i>S. aureus</i> and <i>P. aeruginosa</i> are abundant in CF sputum cultures. Contrary to common assumption, we found no pattern of replacement of <i>S. aureus</i> by <i>P. aeruginosa</i>. Many patients with CF have durable long-term coinfection with these organisms. New strategies are needed to prevent and treat these infections.