Pseudomonas Bacteremia in a Tertiary Hospital and Factors Associated with Mortality

Pseudomonas aeruginosa is the third most commonly identified cause among gram-negative microorganisms causing bloodstream infection (BSI) and carries a very high mortality, higher than that by other gram-negative pathogens. The aim of the present study was to assess the epidemiological and microbiological characteristics of patients with BSI by Pseudomonas spp. in a tertiary hospital, characterize the resistance rates of different Pseudomonas strains to the most clinically relevant anti-microbials, estimate the mortality rate, and identify factors independently associated with mortality. In total, 540 cultures from 419 patients sent to the microbiology department of the hospital during the 8-year period of the study were positive. Patients had a median age of 66 years, and 262 (62.5%) were male. The blood culture was drawn in the ICU in 201 of the patients (48%). The infection was hospital-acquired in 329 patients (78.5%) and the median hospital day when the blood culture was drawn was 15, with a range of 0 to 267 days. Median duration of stay in the hospital was 36 days, hospital mortality was 44.2% (185 patients), and 30-day mortality was 29.6% (124 patients). The most commonly isolated Pseudomonas species were P. aeruginosa followed by P. putida and P. oryzihabitans. There was a statistically significant reduction of P. aeruginosa isolation relative to non-aeruginosa Pseudomonas species in the post-COVID-19 era. Antimicrobial resistance of P. aeruginosa in clinically relevant antimicrobials with anti-pseudomonal activity was similar before and after the onset of the COVID-19 pandemic with the exception of gentamicin and tobramycin, with P. aeruginosa being more susceptible to these two antimicrobials in the post-COVID-19 era. Rates of multi-drug resistant (MDR), extensively-drug resistant (XDR), and difficult-to-treat (DTR) P. aeruginosa isolation were lower after the onset of the COVID-19 pandemic, even though a carbapenem-focused antimicrobial stewardship program had been implemented in the meantime. Increased age, ICU-acquisition of BSI, and more days in the hospital when positive blood culture was drawn were positively associated with 30-day mortality of patients with Pseudomonas BSI. The fact that rates of MDR, XDR, and DTR P. aeruginosa isolation were lower late in the study period, with a carbapenem-focused antimicrobial stewardship intervention being implemented in the meantime, further increases the understanding that implementation of antimicrobial stewardship interventions may halt the increase in antimicrobial resistance noted previously.

Automated summary

This study aimed to assess the epidemiological and microbiological characteristics of patients with bloodstream infection (BSI) caused by Pseudomonas spp. in a tertiary hospital. It found that Pseudomonas aeruginosa was the third most commonly identified cause among gram-negative microorganisms causing BSI, with a high mortality rate. The study also identified factors associated with mortality and observed changes in antimicrobial resistance patterns after the onset of the COVID-19 pandemic.