Pseudomonas aeruginosa is a clinically important organism that infects patients with noncystic fibrosis bronchiectasis (NCFB). In the United States, the estimated prevalence of NCFB is 213 per 100,000 across all age groups and 813 per 100,000 in the over 65 age group.1 A retrospective cohort study suggests the incidence of NCFB as ascertained from International Classification of Diseases codes may significantly underestimate its true prevalence.2
As the incidence of patients with NCFB continues to increase, the impact of the Pseudomonas infection is expected to grow. A recent retrospective cohort study of commercial claims from IQVIA’s PharMetrics Plus database for the period 2006 to 2020 showed that patients with NCFB and Pseudomonas infection had on average 2.58 hospital admissions per year, with a mean length of stay of 9.94 (± 11.06) days, compared with 1.18 admissions per year, with a mean length of stay of 6.5 (± 8.42) days, in patients with Pseudomonas-negative NCFB. The same trend applied to 30-day readmissions and ICU admissions, 1.32 (± 2.51 days) vs 0.47 (± 1.30 days) and 0.95 (± 1.62 days) vs 0.33 (± 0.76 days), respectively. The differential cost of care per patient per year between patients with NCFB with and without Pseudomonas infection ranged from $55,225 to $315,901.3
CHEST
Dr. O'Neil Green
Recent data from the United States Bronchiectasis Registry showed the probability of acquiring Pseudomonas aeruginosa was 3% annually.4 The prevalence of Pseudomonas infection in a large, geographically diverse cohort in the United States was quoted at 15%.5 A retrospective analysis of the European Bronchiectasis Registry database showed Pseudomonas infection was the most commonly isolated pathogen (21.8%).6
Given the high incidence and prevalence of NCFB, the high prevalence of Pseudomonas infection in patients with NCFB, and the associated costs and morbidity from infection, identifying effective treatments has become a priority. The British, Spanish (SEPAR), South African, and European bronchiectasis guidelines outline several antibiotic regimens meant to achieve eradication. Generally, there is induction with a (1) quinolone, (2) β-lactam + aminoglycoside, or (3) quinolone with an inhaled antibiotic followed by three months of maintenance inhaled antibiotics.7-10 SEPAR allows for retreatment for recurrence at any time during the first year with any regimen.
For chronic Pseudomonas infection, SEPAR recommends treatment with inhaled antibiotics for patients with more than two exacerbations or one hospitalization, while the threshold in the British and European guidelines is more than three exacerbations. Azithromycin may be used for those who are intolerant or allergic to the nebulized antibiotics. It is worth noting that in the United States, the antibiotics colistin, ciprofloxacin, aztreonam, gentamicin, and tobramycin are administered off label for this indication. A systematic review found a 10% rate of bronchospasm in the treated group compared with 2.3% in the control group, and premedication with albuterol is often needed.11
Unfortunately, the data supporting the listed eradication and suppressive regimens are weak. A systematic review and meta-analysis of six observational studies including 289 patients showed a 12-month eradication rate of only 40% (95% CI, 34-45; P < 0.00001; I2 = 0).12 These results are disappointing and identify a need for further research into the manner in which Pseudomonas infection interacts with the host lung.
We currently know Pseudomonas infection evades antibiotics and host defenses by accumulating mutations and deletions. These include loss-of-function mutations in mucA (mucoidy), lasR (quorum-sensing), mexS (regulates the antibiotic efflux pump), and other genes related to the production of the polysaccharides Psl and Pel (which contribute to biofilm formation).13 There may also be differences in low and high bacteria microbial networks that interact differently with host cytokines to create an unstable environment that predisposes to exacerbation.14
In an attempt to improve our eradication and suppression rates, investigators have begun to target specific aspects of Pseudomonas infection behavior. The GREAT-2 trial compares gremubamab (a bivalent, bispecific, monoclonal antibody targeting Psl exopolysaccharide and the type 3 secretion system component of PcrV) with placebo in patients with chronic Pseudomonas infection. A phase II trial with the phosphodiesterase inhibitor esifentrine, a phase III trial with a reversible DPP1 inhibitor called brensocatib (ASPEN), and a phase II trial with the CatC inhibitor BI 1291583 (Airleaf) are also being conducted. Each of these agents targets mediators of neutrophil inflammation.
In summary, NCFB with Pseudomonas infection is common and leads to an increase in costs, respiratory exacerbations, and hospitalizations. While eradication and suppression are recommended, they are difficult to achieve and require sustained durations of expensive medications that can be difficult to tolerate. Antibiotic therapies will continue to be studied (the ERASE randomized controlled trial to investigate the efficacy and safety of tobramycin to eradicate Pseudomonas infection is currently underway), but targeted therapies represent a promising new approach to combating this stubbornly resistant bacteria. The NCFB community will be watching closely to see whether medicines targeting molecular behavior and host interaction can achieve what antibiotic regimens thus far have not: consistent and sustainable eradication.
Dr. Green is Assistant Professor in Medicine, Medical Director, Bronchiectasis Program, UMass Chan/Baystate Health, Chest Infections Section, Member-at-Large
References
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