In this study, we investigated predictors of mortality among patients with P. aeruginosa bacteraemia and underscored the importance of ID consultation and timely source control in enhancing outcomes.

The mortality rate in our cohort (22%) was similar to previous research [3,4,5, 8, 11], but lower than studies conducted in regions with higher resistance rates [6, 7, 9, 10]. The relatively low incidence of multidrug resistance among P. aeruginosa isolates, coupled with close monitoring by ID specialists for high-risk patients (such as those undergoing chemotherapy or transplantation), likely contributed to the higher rate of appropriate antimicrobial treatment within the first 48 h of bacteraemia onset in the present study, compared to prior research [2, 3, 6, 7, 10, 11].

The most important finding was the positive impact of ID consultation on managing P. aeruginosa infections, particularly in guiding antimicrobial therapy and source control measures. Consistent with two previous studies on P. aeruginosa bacteraemia, our findings emphasize the importance of ID consultation in improving patient outcomes [8, 11]. The aforementioned studies suffered from survival bias, with only patients surviving long enough receiving ID consultation. One of these studies did not include a timeframe for the realization of ID consultation [8], while the other included ID consultation within two weeks from the onset of bacteraemia [11]. This issue was addressed in our study by implementing a timeframe of 48 h from the onset of bacteraemia. In the present study, the early involvement of ID consultants led to an earlier initiation of appropriate treatment and earlier de-escalation from carbapenems to other beta-lactams with a narrower spectrum. Although the dosages of the administered antimicrobials were not collected in the present study, a previous study from our institution showed that ID consultation among all P. aeruginosa infections led to an increase in the administered dosages of non-carbapenem antibiotics [21]. However, the influence of ID consultation might have been underestimated in our study, as patients at higher risk of mortality, such as those with neutropenia following chemotherapy for hematologic malignancies or undergoing transplantation, were either closely monitored by ID consultants or hospitalized in the ID service, thus de facto receiving consultation within 48 h [3].

In a prior study involving patients with infections due to multidrug-resistant pathogens, ID consultation proved beneficial for methicillin-resistant S. aureus and multidrug-resistant Enterobacteriaceae, but not for P. aeruginosa, likely due to the limited number of patients included with infection caused by this pathogen [22]. Furthermore, although previous research extensively evaluated the effect of appropriate empirical antimicrobial treatment on survival in P. aeruginosa bacteraemia, the role of early source control measures among P. aeruginosa bacteraemic patients was rarely investigated [8]. The impact of timely source control on better outcomes (survival, clearance of bacteraemia or candidaemia) has been demonstrated in various types of infections, such as intra-abdominal infections, necrotizing fasciitis, sepsis, and bloodstream infections caused by different pathogens, including S. aureus, streptococci, and Candida spp [13, 14, 23,24,25,26]. Especially in sepsis which was associated with poorer outcomes in our study, prompt source control is recommended by the Surviving Sepsis Campaign Guidelines to enhance management and improve outcomes [27]. This recommendation is supported by a study on critically ill patients, regardless of the causative pathogen [28].

As previously demonstrated, an elevated Charlson comorbidity index, which encompasses age and various comorbid conditions, was correlated with increased 30-day mortality [1,2,3, 7, 8, 10, 11]. Previous research has highlighted the significance of the focus of infection in determining outcomes, with bacteraemias secondary to lower respiratory tract or pulmonary infections associated with worse prognoses [1, 2, 29, 30].

In prior studies, the time to positivity of blood cultures, serving as an indirect measure of the microbial load of the infecting organism, was found to be indicative of poorer outcomes among patients with P. aeruginosa bacteraemia [29, 30]. No such correlation was identified in the current study, underscoring the limitations in evaluating the time to positivity of blood cultures. Variability in protocols for blood culture drawing, processing, and incubation across different centers can lead to discrepancies in the time to positivity results.

The current study is subject to several limitations. Firstly, it was a retrospective analysis conducted at a single center in a setting with low resistance rates, thus caution must be exercised when generalizing our findings, particularly to settings with higher resistance rates. Moreover, factors such as decisions to restrict treatment and the readiness of surgeons or interventional radiologists to undertake source control procedures could influence the relationship between outcome and prompt interventions. In our study, among episodes warranting source control intervention, only three patients succumbed or had care withdrawn within the 48-hour timeframe, minimizing their impact on our results.

In conclusion, we have demonstrated the beneficial role of timely ID consultation in patients with P. aeruginosa bacteraemia, aligning it with other pathogens such as S. aureus, Candida spp., enterococci, and streptococci, thereby advocating for ID consultation as an integral component of management to enhance patient outcomes. Additionally, we have underscored the importance of implementing source control interventions when appropriate. Future studies are needed to evaluate the impact of comprehensive approach with early interventions such as ID consultation, tailored antimicrobial treatment, and source control in enhancing patient outcomes.