Antibiotic exposure and resistance development in Pseudomonas aeruginosa and Enterobacter species in intensive care units

The Distribution, Drug Susceptibility, and Dynamic Trends of Pseudomonas aeruginosa Infection in a Tertiary Hospital in China During 2016‒2022

Background

Drug-resistant Pseudomonas aeruginosa infections rapidly increased and contributed to life-threatening nosocomial infections; however, the distribution, species, drug susceptibility and dynamic trends of P. aeruginosa infection in China remained unclear. This study was conducted to better understand the epidemiological data of increased P. aeruginosa infections from 2016 to 2022 in a hospital in China.

Methods

This study involved 3301 patients infected with P. aeruginosa, diagnosed using a nosocomial infection surveillance system in a tertiary hospital between 2016 and 2022. The P. aeruginosa infections from 2016 to 2022 were assessed according to the hospital department and species, and the drug susceptibility was evaluated using 16 antimicrobial agents.

Results

The P. aeruginosa infection prevalence in the hospital department was: Neurosurgery (14.30%), Emergency (13.30%), and Critical Care Medicine (11.69%). Samples for P. aeruginosa infection identification were from sputum (72.52%) and other secreta (9.91%). The P. aeruginosa infections demonstrated a greater sensitivity to amikacin (AMK, 91.82%), tobramycin (TOB, 82.79%), and gentamycin (GEN, 82.01%); however, P. aeruginosa infection demonstrated greater resistance to ticarcillin (22.57%), levofloxacin (21.63%), and ciprofloxacin (18.00%).

Conclusion

The P. aeruginosa infections were commonly observed in the Neurosurgery, Emergency, and Critical Care Medicine departments and demonstrated greater sensitivity to AMK, TOB, and GEN than the other drugs.

Progression of Kidney Injury with the Combination of Vancomycin and Piperacillin-Tazobactam or Cefepime in Sepsis-Associated Acute Kidney Injury

INTRODUCTION

The combination of vancomycin/piperacillin-tazobactam is associated with increases in serum creatinine compared to other antibiotic combinations in the treatment of infections for hospitalized patients. However, the available literature is limited to the study of incident acute kidney injury (AKI). The combination has not been evaluated in patients with AKI already present and the degree to which the trajectory of AKI is influenced by this combination is unknown.

METHODS

This was a single center, retrospective cohort study of adult patients with sepsis and AKI present on admission prescribed a combination of vancomycin with either piperacillin-tazobactam or cefepime within the first 3 days of admission. The primary outcome was maximum serum creatinine observed within days 2-7 of the hospital stay. Subsequent kidney outcomes were evaluated at one week and hospital discharge.

RESULTS

Of 480 patients with sepsis and AKI who met inclusion criteria, 288 (60%) received vancomycin/piperacillin-tazobactam, and 192 (40%) received vancomycin/cefepime. Patients were well-matched on clinical factors, including severity of illness, stage of AKI, exposure to other nephrotoxins, and durations of antimicrobial therapy. There were no differences in AKI trajectory during the first week as assessed by maximum serum creatinine (2.1 (1.4-3.5) mg/dl vs. 2.1 (1.4-3.0) mg/dl; p=0.459) and AKI progression (24.0% vs. 23.4%; p=0.895). No differences were observed with other kidney related outcomes, including the need for dialysis (14.6% vs. 13.0%; p=0.628) or major adverse kidney events at hospital discharge (48.3% vs. 47.9%; p=0.941).

CONCLUSIONS

In patients with sepsis and AKI, the combination of vancomycin/piperacillin-tazobactam compared to vancomycin/cefepime was not associated with higher serum creatinine values or AKI progression in the week following ICU admission.

The problem of multi-resistance in gram-negative bacilli in intensive care units: Treatment and prevention strategies

The rise of infections caused by multi-resistant gram-negative bacilli (MR-GNB), which includes carbapenems, represents one of the major current challenges worldwide. These MR-GNB include extended spectrum β-lactamase-producing Enterobacterales, derepressed AmpC-producing or carbapenemase-producing Enterobacterales as well as non-fermenting Gram-negative bacilli such as Pseudomonas aeruginosa or Acinetobacter baumannii. P. aeruginosa predominantly exhibits other resistance mechanisms different to β-lactamases such as expulsion pumps or loss of porins. A. baumannii frequently presents several of these resistance mechanisms. Mortality is high especially if empirical treatment is inadequate. In this review, treatment strategies are revised, describing the tools available to identify patients in whom empirical antibiotic treatment would be justified to cover MR-GNB, the importance of optimizing the administration of these antibiotics, as well as prevention strategies to avoid its spread from patients colonized or infected by a MR-GNB.

Rapid expansion and extinction of antibiotic resistance mutations during treatment of acute bacterial respiratory infections

Acute bacterial infections are often treated empirically, with the choice of antibiotic therapy updated during treatment. The effects of such rapid antibiotic switching on the evolution of antibiotic resistance in individual patients are poorly understood. Here we find that low-frequency antibiotic resistance mutations emerge, contract, and even go to extinction within days of changes in therapy. We analyzed Pseudomonas aeruginosa populations in sputum samples collected serially from 7 mechanically ventilated patients at the onset of respiratory infection. Combining short- and long-read sequencing and resistance phenotyping of 420 isolates revealed that while new infections are near-clonal, reflecting a recent colonization bottleneck, resistance mutations could emerge at low frequencies within days of therapy. We then measured the in vivo frequencies of select resistance mutations in intact sputum samples with resistance-targeted deep amplicon sequencing (RETRA-Seq), which revealed that rare resistance mutations not detected by clinically used culture-based methods can increase by nearly 40-fold over 5–12 days in response to antibiotic changes. Conversely, mutations conferring resistance to antibiotics not administered diminish and even go to extinction. Our results underscore how therapy choice shapes the dynamics of low-frequency resistance mutations at short time scales, and the findings provide a possibility for driving resistance mutations to extinction during early stages of infection by designing patient-specific antibiotic cycling strategies informed by deep genomic surveillance.

It remains unclear how rapid antibiotic switching affects the evolution of antibiotic resistance in individual patients. Here, Chung et al. combine short- and long-read sequencing and resistance phenotyping of 420 serial isolates of Pseudomonas aeruginosa collected from the onset of respiratory infection, and show that rare resistance mutations can increase by nearly 40-fold over 5–12 days in response to antibiotic changes, while mutations conferring resistance to antibiotics not administered diminish and even go to extinction.

Antibiotic exposure and acquisition of antibiotic-resistant gram-negative bacteria among outpatients at a US Veterans Affairs medical center

Objectives:

To assess the prevalence of antibiotic-resistant gram-negative bacteria (R-GNB) among patients without recent hospitalization and to examine the influence of outpatient antibiotic exposure on the risk of acquiring R-GNB in this population.

Design:

2-year retrospective cohort study.

Setting:

Regional Veterans Affairs healthcare system.

Patients:

Outpatients at 13 community-based clinics.

Methods:

We examined the rate of acquisition of R-GNB within 90 days following an outpatient visit from 2018 to 2019. We used clinical and administrative databases to determine and summarize prescriptions for systemic antibiotics, associated infectious diagnoses, and subsequent R-GNB acquisition among patients without recent hospitalizations. We also calculated the odds ratio of R-GNB acquisition following antibiotic exposure.

Results:

During the 2-year study period, 7,215 patients had outpatient visits with microbiological cultures obtained within 90 days. Of these patients, 206 (2.9%) acquired an R-GNB. Among patients receiving antibiotics at the visit, 4.6% acquired a R-GNB compared to 2.7% among patients who did not receive antibiotics, yielding an unadjusted odds ratio of 1.75 (95% confidence interval, 1.18–2.52) for a R-GNB following an outpatient visit with versus without an antibiotic exposure. Regardless of R-GNB occurrence, >50% of antibiotic prescriptions were issued at visits without an infectious disease diagnosis or issued without documentation of an in-person or telehealth clinical encounter.

Conclusions:

Although the rate of R-GNBs was low (2.9%), the 1.75-fold increased odds of acquiring a R-GNB following an outpatient antibiotic highlights the importance of antimicrobial stewardship efforts in outpatient settings. Specific opportunities include reducing antibiotics prescribed without an infectious diagnosis or a clinical visit.

Development of a rapid and sensitive analytical system for Pseudomonas aeruginosa based on reverse transcription quantitative PCR targeting of rRNA molecules

For Pseudomonas aeruginosa (PA), infection control and appropriate antimicrobial treatment have become important issues. Diagnosis is critical in managing PA infection, but conventional methods are not highly accurate or rapid. We developed a new PA quantification system based on 23S rRNA-targeted reverse transcription quantitative PCR (RT-qPCR). We confirmed that RT-qPCR can quantify PA directly from clinical samples quickly (within 6 h) and with high sensitivity (blood, 1 cell/mL; stool, 100 cells/g) and without cross-reaction. Also, under antibiotic treatment, PA viable counts detected by this system correlated well with the inflammatory response of infected Caco-2 cells compared to other methods such as culturing and qPCR. Next, we utilized this system on fecal samples collected from 65 septic ICU patients and 44 healthy volunteers to identify ICU infection status. We confirmed that the PA detection ratio in ICU patients was significantly higher than that in healthy volunteers (49.2% vs. 13.6%, P < 0.05). Additionally, we monitored drug-resistant PA in 4 ICU patients by this system. The trends in PA counts accurately reflected various treatment backgrounds such as antibiotic use and mechanical ventilator use. Our results suggest that this RT-qPCR system is beneficial for the early diagnosis and evaluation of appropriate antibacterial treatment and may be a useful tool in combating PA infection.

Emergence of non-susceptibility during persistent Pseudomonas aeruginosa bacteraemia in haematopoietic cell transplant recipients and haematological malignancy patients

Background

Systematic studies pertaining to the emergence of resistance during therapy of Pseudomonas aeruginosa bloodstream infections (BSIs) in haematopoietic cell transplant (HCT) recipients and haematological malignancy (HM) patients are lacking.

Objectives

To determine how frequently non-susceptibility emerges during therapy of P. aeruginosa BSIs and to compare these findings with non-HCT/HM patients.

Patients and methods

P. aeruginosa BSIs that occurred at our institution between 1 July 2012 and 31 October 2019 in HCT/HM patients and non-HCT/HM patients were identified. Episodes in which bacteraemia persisted while on appropriate therapy (‘persistent BSI’) were evaluated for emergence of non-susceptibility during therapy.

Results

In total, 96 BSI episodes among 86 HCT/HM patients were analysed. Eight persistent BSI episodes (8.3%) occurred in eight patients (9.3%). Repeat susceptibility testing was performed in seven (87.5%) of these episodes. Non-susceptibility to the treatment agent emerged in five (71.4%) episodes and to any antipseudomonal agent in seven (100%) episodes. The 21 day mortality rate associated with persistent BSI was 87.5% (seven of eight), and it was 80% (four of five) among persistent BSI episodes in which non-susceptibility to the treatment agent emerged on therapy. Non-susceptibility to any antipseudomonal agent during persistent BSI emerged significantly more frequently in HCT/HM patients compared with non-HCT/HM patients.

Conclusions

Non-susceptibility emerges frequently during persistent P. aeruginosa BSIs in HCT/HM patients, and this is associated with a high mortality rate. Our findings have implications for the management of persistent P. aeruginosa BSIs in these patients. Larger studies are needed to confirm and expand on our findings.

Duration of antimicrobial therapy for Gram-negative infections

PURPOSE OF REVIEW

The potential benefits on antimicrobial resistance emergence, incidence of antibiotic-related adverse effects, and health costs have pushed to shorten therapeutic courses for Gram-negative bacilli (GNB) infections. However, the safety of this approach is still under investigation. This review gathers recent contributions to the evaluation of the impact on antimicrobial resistance and clinical outcome of shorter therapeutic courses against GNB infections, and highlights data on the modern approach of adjustable antibiotic duration.

RECENT FINDINGS

Recent advances include data on the safety of 7-day treatment of uncomplicated Enterobacteriaceae bloodstream infections with favorable early 48-h evolution. A promising innovative approach with individualized treatment duration arises, supported by recently published results on GNB bacteremia evaluating fixed antibiotic durations and an adaptive antibiotic duration driven by blood levels of C-reactive protein.

SUMMARY

Recent literature illustrates a strong trend towards shortened antibiotic durations in GNB infections, illustrated by lately published data in GNB bacteremia and ongoing studies in GNB ventilator-associated pneumonia. However, short antibiotic course for specific situations, such as immunodeficiency, drug-resistance, and inadequate source control should be handled with caution because of lack of supportive data.

Population Pharmacokinetics and Probability of Target Attainment of Different Dosing Regimens of Ceftazidime in Critically Ill Patients with a Proven or Suspected Pseudomonas aeruginosa Infection

Altered pharmacokinetics (PK) of hydrophilic antibiotics in critically ill patients is common, with possible consequences for efficacy and resistance. We aimed to describe ceftazidime population PK in critically ill patients with a proven or suspected Pseudomonas aeruginosa infection and to establish optimal dosing. Blood samples were collected for ceftazidime concentration measurement. A population PK model was constructed, and probability of target attainment (PTA) was assessed for targets 100% T > MIC and 100% T > 4 × MIC in the first 24 h. Ninety-six patients yielded 368 ceftazidime concentrations. In a one-compartment model, variability in ceftazidime clearance (CL) showed association with CVVH. For patients not receiving CVVH, variability in ceftazidime CL was 103.4% and showed positive associations with creatinine clearance and with the comorbidities hematologic malignancy, trauma or head injury, explaining 65.2% of variability. For patients treated for at least 24 h and assuming a worst-case MIC of 8 mg/L, PTA was 77% for 100% T > MIC and 14% for 100% T > 4 × MIC. Patients receiving loading doses before continuous infusion demonstrated higher PTA than patients who did not (100% T > MIC: 95% (n = 65) vs. 13% (n = 15); p < 0.001 and 100% T > 4 × MIC: 20% vs. 0%; p = 0.058). The considerable IIV in ceftazidime PK in ICU patients could largely be explained by renal function, CVVH use and several comorbidities. Critically ill patients are at risk for underexposure to ceftazidime when empirically aiming for the breakpoint MIC for P. aeruginosa. A loading dose is recommended.

Multiple cross displacement amplification-a more applicable technique in detecting Pseudomonas aeruginosa of ventilator-associated pneumonia (VAP)

Background

Early and rapid identification of Pseudomonas aeruginosa (P. aeruginosa) in patients with suspected ventilator-associated pneumonia (VAP) provides theoretical clinical advantages in therapeutic optimization strategies.

Methods

The P. aeruginosa-multiple cross displacement amplification (PA-MCDA) assay was conducted at an isothermal temperature during the amplification stage, and products were visually detected by color changes. The entire process was completed within 1 h. A total of 77 strains, including P. aeruginosa species and various other species of non-P. aeruginosa, were used to evaluate PA-MCDA assays. Bronchoalveolar lavage fluid (BALF) of suspected VAP patients was examined by the MCDA assay.

Results

The MCDA assay exhibited a 100% analytical specificity in detecting PA from all 77 strains, and the limit of detection was as low as 100 fg DNA per reaction. A temperature of 65 °C was recommended as standard during the amplification stage. The agreement between PA-MCDA and bacteria culture was 91.18% (κ = 0.787; p = 0.000) in the identification of P. aeruginosa in BALF from suspected VAP. The PA-MCDA assay showed values of 92.31%, 90.78%, 77.41%, and 97.18% for sensitivity, specificity, positive predictive value, and negative predictive value, respectively. PA-MCDA had a higher detective rate of P. aeruginosa than bacteria culture in patients with antipseudomonal therapy.

Conclusions

The instrument-free platform of the MCDA assay makes it a simple, rapid, and applicable procedure for “on-site” diagnosis and point-of-care testing for the presence of P. aeruginosa without the need for specific bacterial culture.

Risk Factors of Initial Inappropriate Antibiotic Therapy and the Impacts on Outcomes of Neonates with Gram-Negative Bacteremia

BACKGROUND

Timely appropriate empirical antibiotic plays an important role in critically ill patients with gram-negative bacteremia. However, the relevant data and significant impacts have not been well studied in the neonatal intensive care unit (NICU).

METHODS

An 8-year (1 January 2007-31 December 2014) cohort study of all NICU patients with gram-negative bacteremia (GNB) in a tertiary-care medical center was performed. Inadequate empirical antibiotic therapy was defined when a patient did not receive any antimicrobial agent to which the causative microorganisms were susceptible within 24 h of blood culture sampling. Neonates with GNB treated with inadequate antibiotics were compared with those who received initial adequate antibiotics.

RESULTS

Among 376 episodes of Gram-negative bacteremia, 75 (19.9%) received inadequate empirical antibiotic therapy. The cause of inadequate treatment was mostly due to the pathogen resistance to prescribed antibiotics (88.0%). Bacteremia caused by Pseudomonas aeruginosa (Odds ratio [OR]: 20.8, P < 0.001) and extended spectrum β-lactamase (ESBL)-producing bacteria (OR: 18.4, P < 0.001) had the highest risk of inadequate treatment. Previous exposure with third generation cephalosporin was identified as the only independent risk factor (OR: 2.52, 95% CI: 1.18-5.37, P = 0.018). Empirically inadequately treated bacteremias were significantly more likely to have worse outcomes than those with adequate therapy, including a higher risk of major organ damage (20.0% versus 6.6%, P < 0.001) and infectious complications (25.3% versus 9.3%, P < 0.001), and overall mortality (22.7% versus 11.0%, P = 0.013). Conclusions: Inadequate empirical antibiotic therapy occurs in one-fifth of Gram-negative bacteremias in the NICU, and is associated with worse outcomes. Additional prospective studies are needed to elucidate the optimal timing and aggressive antibiotic regimen for neonates who are at risk of antibiotic-resistant Gram-negative bacteremia.

Changes of resistance rates in Pseudomonas aeruginosa strains are unrelated to antimicrobial consumption in ICU populations with invasive device-related infection

OBJECTIVE

To evaluate the relationship between antipseudomonal antibiotic consumption and each individual drug resistance rate in Pseudomonas aeruginosa strains causing ICU acquired invasive device-related infections (IDRI).

DESIGN

A post hoc analysis was made of the data collected prospectively from the ENVIN-HELICS registry.

SETTING

Intensive Care Units participating in the ENVIN-UCI registry between the years 2007 and 2016 (3-month registry each year).

PATIENTS

Patients admitted for over 24h.

MAIN VARIABLES

Annual linear and nonlinear trends of resistance rates of P. aeruginosa strains identified in IDRI and days of treatment of each antipseudomonal antibiotic family per 1000 occupied ICU bed days (DOT) were calculated.

RESULTS

A total of 15,095 episodes of IDRI were diagnosed in 11,652 patients (6.2% out of a total of 187,100). Pseudomonas aeruginosa was identified in 2095 (13.6%) of 15,432 pathogens causing IDRI. Resistance increased significantly over the study period for piperacillin-tazobactam (P<0.001), imipenem (P=0.016), meropenem (P=0.004), ceftazidime (P=0.005) and cefepime (P=0.015), while variations in resistance rates for amikacin, ciprofloxacin, levofloxacin and colistin proved nonsignificant. A significant DOT decrease was observed for aminoglycosides (P<0.001), cephalosporins (P<0.001), quinolones (P<0.001) and carbapenems (P<0.001).

CONCLUSIONS

No significant association was observed between consumption of each antipseudomonal antibiotic family and the respective resistance rates for P. aeruginosa strains identified in IDRI.

Risk factors and the resistance mechanisms involved in Pseudomonas aeruginosa mutation in critically ill patients

Background

The objective of this study was to determine the main risk factors of Pseudomonas aeruginosa mutation as well as the mechanisms of acquired resistance.

Methods

We conducted a 2-year prospective study in patients who were carriers of a Pseudomonas aeruginosa strain and who had been admitted to a medical/surgical ICU.

Results

Of the 153 patients who were included, 34 had a mutation in their strain. In a multivariate analysis, a duration of ventilation > 24 days was a risk factor for mutation (risk ratio 4.29; CI 95% 1.94-9.49) while initial resistance was a protective factor (RR 0.36; CI 95% 0.18-0.71). In a univariate analysis, exposure of P. aeruginosa to ceftazidime was associated with an over-production of AmpC cephalosporinase and exposure to meropenem was associated with impermeability. A segmentation method based on the duration of ventilation (> 24 days), initial resistance, and exposure of strains to ceftazidime made it possible to predict at 83% the occurrence of mutation.

Conclusion

The duration of ventilation and the presence of resistance as soon as P. aeruginosa is identified are predictive factors of mutation in ICU patients.

The intervention by an antimicrobial stewardship team can improve clinical and microbiological outcomes of resistant gram-negative bacteria

Antibiotic stewardship (AS) improves patient outcomes and rates of antibiotic susceptibilities. However, the long-term effect of AS programs (ASPs) on mortality is unclear. This study aimed to assess the impact of bedside interventions by an AS team (AST) on clinical and microbiological outcomes. This retrospective study enrolled patients with bloodstream infections (BSI) and long-term use of broad-spectrum antibiotics (more than 7 days). The main outcomes were 30-day and in-hospital mortality of patients with BSI. The secondary outcomes were the day of therapy (DOT) and susceptibility of antipseudomonal agents. Cases were classified into two groups: the pre-ASP group comprised cases between 2011 and 2013 and the post-ASP group, between 2014 and 2016. The outcomes were then compared between the two groups. Among the patients with all BSI (n = 1187), no significant differences in 30-day mortality were observed between those in the pre-ASP and post-ASP groups. However, in-hospital mortality was significantly lower in the post-ASP group than that in the pre-ASP group (24.8% vs. 18.0%; P = 0.004). Furthermore, the 30-day and in-hospital mortality of resistant gram-negative bacteraemia was significantly lower (20.4% vs.10.5%; P = 0.04 and 28.0% vs.16.1%; P = 0.03). The DOT of broad-spectrum antibiotics decreased except that of tazobactam/piperacillin. The susceptibilities of tazobactam/piperacillin, ceftazidime, cefepime, sulbactam/cefoperazone, gentamicin, ciprofloxacin levofloxacin, imipenem and meropenem were significantly better. Interventions by the AST can improve the clinical and microbiological outcomes, especially resistant gram-negative bacteria. Furthermore, this effect of our ASP can continue for a long term.

Duration of Exposure to Antipseudomonal β-Lactam Antibiotics in the Critically Ill and Development of New Resistance

STUDY OBJECTIVE

Minimizing the duration of broad-spectrum antimicrobial exposure in the critically ill is a commonly used strategy aimed at preventing resistance. Our objective was to correlate the duration of exposure to antipseudomonal β-lactam antibiotics with the development of new resistance in critically ill patients.

DESIGN

Single-center, retrospective cohort study.

SETTING

A large, academic, tertiary care hospital.

PATIENTS

A total of 7118 adults with a discharge diagnosis of severe sepsis or septic shock who received at least one dose of cefepime, meropenem, or piperacillin-tazobactam during their hospitalization between 2010 and 2015.

MEASUREMENTS AND MAIN RESULTS

Cohort entry was defined as the first day of any antipseudomonal β-lactam initiation, and exposure was defined as the cumulative days of any antipseudomonal β-lactam exposure during the 60-day follow-up period. The primary outcome was development of new resistance to any antipseudomonal β-lactam > 3 days after cohort entry. New resistance was defined as detection of resistance to any antipseudomonal β-lactam not identified within 180 days before cohort entry. Patients without an outcome (i.e., did not develop new resistance) or who died by day 60 were censored. Cox proportional hazards models were performed to assess the risk of development of new resistance to any antipseudomonal β-lactam with each additional day of exposure. Analyses of each individual antipseudomonal β-lactam were evaluated as secondary outcomes. Each additional day of exposure to any antipseudomonal β-lactam resulted in an adjusted hazard ratio (aHR) of 1.04 (95% confidence interval [CI] 1.04-1.05) for new resistance development. The risk of developing new resistance to cefepime, meropenem, and piperacillin-tazobactam for each additional day of exposure resulted in an aHR of 1.08 (95% CI 1.07-1.09), 1.02 (95% CI 1.01-1.03), and 1.08 (95% CI 1.06-1.09), respectively.

CONCLUSION

Among critically ill patients who receive antipseudomonal β-lactam antibiotics, each additional day of exposure to cefepime, meropenem, and piperacillin-tazobactam is associated with an increased risk of new resistance development.

Long-term use of selective digestive decontamination in an ICU highly endemic for bacterial resistance

BACKGROUND

We examined whether long-term use of selective digestive tract decontamination (SDD) was effective in reducing intensive care unit (ICU)-acquired infection and antibiotic consumption while decreasing colistin-, tobramycin-, and most of the antibiotic-resistant colonization rates in a mixed ICU with a high endemic level of multidrug-resistant bacteria (MDRB).

METHODS

In this cohort study, which was conducted in a 30-bed medical-surgical ICU, clinical outcomes before (1 year, non-SDD group) and after (4 years) implementation of SDD were compared. ICU patients who were expected to require tracheal intubation for > 48 hours were given a standard prophylactic SDD regimen. Oropharyngeal and rectal swabs were obtained on admission and once weekly thereafter.

RESULTS

ICU-acquired infections occurred in 110 patients in the non-SDD group and in 258 in the SDD group. A significant (P <  0.001) reduction of infections caused by MDRB (risk ratio [RR], 0.31; 95% CI, 0.23-0.41) was found after SDD and was associated with low rates of colistin- and tobramycin-resistant colonization. Colistin- and tobramycin-acquired increasing rate of ICU colonization resistance by 1000 days, adjusted by the rate of resistances at admission, was nonsignificant (0.82; 95% CI, 0.56 to 1.95; 1.13; 95% CI, 0.75 to 1.70, respectively). SDD was also a protective factor for ICU-acquired infections caused by MDR gram-negative pathogens and Acinetobacter baumannii in the multivariate analysis. In addition, a significant (P <  0.001) reduction of ventilator-associated pneumonia (VAP) (RR, 0.43; 95% CI, 0.32-0.59) and secondary bloodstream infection (BSI) (RR, 0.35; 95% CI, 0.24-0.52) was found. A decrease in antibiotic consumption was also observed.

CONCLUSIONS

Treatment with SDD during 4 years was effective in an ICU setting with a high level of resistance, with clinically relevant reductions of infections caused by MDRB, and with low rates of colistin- and tobramycin-resistant colonization with nonsignificant increasing rate of ICU colonization resistance by 1000 days, adjusted by the rate of resistances at ICU admission. In addition, VAP and secondary BSI rates were significantly lower after SDD. Notably, a decrease in antimicrobial consumption was also observed.

Prediction of imipenem-resistant microorganisms among the nosocomial critically ill patients with Gram-negative bacilli septicemia: a simple risk score

Objectives

The increasing number of reports on infections due to carbapenem-resistant Gram-negative bacilli (GNB) has raised concerns, because they have complicated empiric or guided antibiotic therapy for critically ill patients. We aimed to develop a scoring system to predict nosocomial imipenem-resistant GNB (IR-GNB) septicemia among the critically ill patients.

Materials and methods

The study included critically ill adult patients with nosocomial GNB septicemia at Kaohsiung Chang Gung Memorial Hospital (CGMH) in 2013-2015, and the scoring system for predicting IR-GNB septicemia was developed, followed by prospective validation conducted among patients at Linkou CGMH and Kaohsiung CGMH between January and June, 2016.

Results

In the development of the scoring system, 748 patients were included. The independent factors associated with IR-GNB septicemia were prior exposure (days) to carbapenems (adjusted odds ratio [aOR] per 1-day increase, 1.1; 1-3 days: 2 points, 4-6 days: 5 points, 7-9 days: 8 points, and ≥10 days: 13 points), use of mechanical ventilation (aOR 3.7; 5 points), prior colonization with IR-GNB strains (aOR 3.5; 5 points) within 30 days before the onset of GNB septicemia, and comorbid condition with chronic kidney disease (aOR 2.1; 3 points). The internal validation showed an area under the receiver operating characteristic curve (ROC) of 0.75; and an external validation among 314 patients showed similarly good performance (ROC 0.77). Youden's index indicated the score of ≥6 as the best cutoff value with sensitivity of 75% and specificity of 79%.

Conclusion

This scoring system might help clinicians stratify the risk for developing IR-GNB septicemia among critically ill patients and combined antibiotics may be used until antimicrobial de-escalation/adjustment is clearly indicated by the subsequently identified GNB and its susceptibility profile.

A nationwide survey of intravenous antimicrobial use in intensive care units in Japan

Although most patients in the intensive care unit (ICU) receive antibiotics, little is known about patterns of antibiotic use in ICUs in Japan. The objective of this study was to evaluate the pattern of antibiotic use in ICUs. A nationwide one-day cross-sectional surveillance of antibiotic use in the ICU was conducted three times between January 2011 and December 2011. All patients aged at least16 years were included. Data from 52 ICUs and 1148 patients were reviewed. There were 1028 prescriptions for intravenous antibiotics. Of 1148 patients, 834 (73%) received at least one intravenous antibiotic, and 575 had at least one known site of infection. Respiratory and intra-abdominal infections were the two most common types. Of 1028 prescriptions, 331 (34%) were for surgical or medical prophylaxis. Excluding prophylaxis, carbapenems were the most commonly prescribed agent. Infectious disease consultations, pre- and post-prescription antimicrobial stewardship, and ICU-dedicated antibiograms were available in 44%, 52%, 77%, and 21% of the ICUs, respectively. In logistic regression analysis adjusting for patient characteristics, treatment in a university hospital (adjusted odds ratio, 1.72; 95% CI, 1.05-2.84; P = 0.033) and an open ICU (adjusted odds ratio, 2.30; 95% CI, 1.02-5.17; P = 0.044) were significantly associated with greater likelihood of carbapenem use. An increase in the number of closed ICUs and more intensive care specialists may reduce carbapenem use in Japanese ICUs. Large-scale epidemiological studies of antimicrobial resistance in the ICU are needed.

The effects of antibiotic cycling and mixing on antibiotic resistance in intensive care units: a cluster-randomised crossover trial

BACKGROUND

Whether antibiotic rotation strategies reduce prevalence of antibiotic-resistant, Gram-negative bacteria in intensive care units (ICUs) has not been accurately established. We aimed to assess whether cycling of antibiotics compared with a mixing strategy (changing antibiotic to an alternative class for each consecutive patient) would reduce the prevalence of antibiotic-resistant, Gram-negative bacteria in European intensive care units (ICUs).

METHODS

In a cluster-randomised crossover study, we randomly assigned ICUs to use one of three antibiotic groups (third-generation or fourth-generation cephalosporins, piperacillin-tazobactam, and carbapenems) as preferred empirical treatment during 6-week periods (cycling) or to change preference after every consecutively treated patient (mixing). Computer-based randomisation of intervention and rotated antibiotic sequence was done centrally. Cycling or mixing was applied for 9 months; then, following a washout period, the alternative strategy was implemented. We defined antibiotic-resistant, Gram-negative bacteria as Enterobacteriaceae with extended-spectrum β-lactamase production or piperacillin-tazobactam resistance, and Acinetobacter spp and Pseudomonas aeruginosa with piperacillin-tazobactam or carbapenem resistance. Data were collected for all admissions during the study. The primary endpoint was average, unit-wide, monthly point prevalence of antibiotic-resistant, Gram-negative bacteria in respiratory and perineal swabs with adjustment for potential confounders. This trial is registered with ClinicalTrials.gov, number NCT01293071.

FINDINGS

Eight ICUs (from Belgium, France, Germany, Portugal, and Slovenia) were randomly assigned and patients enrolled from June 27, 2011, to Feb 16, 2014. 4069 patients were admitted during the cycling periods in total and 4707 were admitted during the mixing periods. Of these, 745 patients during cycling and 853 patients during mixing were present during the monthly point-prevalence surveys, and were included in the main analysis. Mean prevalence of the composite primary endpoint was 23% (168/745) during cycling and 22% (184/853) during mixing (p=0·64), yielding an adjusted incidence rate ratio during mixing of 1·039 (95% CI 0·837-1·291; p=0·73). There was no difference in all-cause in-ICU mortality between intervention periods.

INTERPRETATION

Antibiotic cycling does not reduce the prevalence of carriage of antibiotic-resistant, Gram-negative bacteria in patients admitted to the ICU.

FUNDING

European Union Seventh Framework Programme.

Emergence of antimicrobial resistance to Pseudomonas aeruginosa in the intensive care unit: association with the duration of antibiotic exposure and mode of administration

Background

Antibiotics are frequently used in intensive care units (ICUs), and their use is associated with the emergence of bacterial resistance to antibiotics. The aim of this study was to investigate the association between the emergence of Pseudomonas aeruginosa resistance and the duration of antibiotic exposure or mode of administration in an ICU unit.

Methods

A 4-year cohort study of intensive care unit was performed in patients with P. aeruginosa isolates from clinical specimens, initially susceptible to the investigated antibiotics (piperacillin/tazobactam, ceftazidime, ciprofloxacin, meropenem and amikacin). Odds ratios (ORs) with 95% confidence interval (95% CI) of emergence of resistance were calculated using logistic regression analysis for various exposure periods to antibiotics (1–3, 4–7, 8–15 and >15 days) relative to no exposure with adjustment for age, sex, Simplified Acute Physiology Score 3 (SAPS 3) and length of stay. ORs on the emergence of P. aeruginosa resistance were also calculated for the various modes of administration.

Results

Included were 187 patients [mean age 61 years, 69% male, mean SAPS 3 score (SD): 59 (12.3)]. None of the antibiotics investigated showed the emergence of resistance within 1–3 days. Significant meropenem resistance emerged within 8–15 days [OR 79.1 (14.9–421.0)] after antibiotic exposure unlike other antibiotics (>15 days). No difference was observed between intermittent and extended administration of meropenem and between beta-lactam mono- or combined therapy.

Conclusions

Use of meropenem was associated with the emergence of resistance as soon as 8 days after exposure to the antibiotic.

Predicting and preventing antimicrobial resistance utilizing pharmacodynamics: part II Gram-negative bacteria

INTRODUCTION

Antimicrobial resistance is a serious health threat worldwide. Better understanding of exposure targets that could suppress resistance amplification is necessary to guide the dosing of currently available agents as well as new therapies in the drug development process. Areas covered: This review will discuss studies that focused on predicting development of resistance using the pharmacokinetic-pharmacodynamic approach and how to design dosing regimens that can successfully suppress resistance emergence in Gram-negative bacteria. Expert opinion: Pharmacokinetic-pharmacodynamic targets could provide useful insights to guide antimicrobial dosing to prevent resistance emergence. Exposure targets required for resistance suppression are higher than those for efficacy and might not be clinically feasible. Combination therapy is a possible approach to improve the efficacy and minimize the resistance emergence for difficult-to-treat infections.

Evaluating the Impact of Antibiotic Exposures as Time-Dependent Variables on the Acquisition of Carbapenem-Resistant Acinetobacter baumannii

OBJECTIVES

To determine the time-dependent effect of antibiotics on the initial acquisition of carbapenem-resistant Acinetobacter baumannii.

DESIGN

Retrospective cohort study.

SETTING

Forty-bed trauma ICU in Miami, FL.

PATIENTS

All consecutive patients admitted to the unit from November 1, 2010, to November 30, 2011.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients underwent surveillance cultures at admission to the unit and weekly thereafter. The primary outcome was the acquisition of carbapenem-resistant A. baumannii on surveillance cultures. Daily antibiotic exposures during the time of observation were used to construct time-dependent variables, including cumulative exposures (in grams and daily observed doses [defined daily doses]). Among 360 patients, 45 (12.5%) became colonized with carbapenem-resistant A. baumannii. Adjusted Cox models showed that each additional point in the Acute Physiologic and Chronic Health Evaluation score increased the hazard by 4.8% (hazard ratio, 1.048; 95% CI, 1.010-1.087; p = 0.0124) and time-dependent exposure to carbapenems quadrupled the hazard (hazard ratio, 4.087; 95% CI, 1.873-8.920; p = 0.0004) of acquiring carbapenem-resistant A. baumannii. Additionally, adjusted Cox models determined that every additional carbapenem defined daily dose increased the hazard of acquiring carbapenem-resistant A. baumannii by 5.1% (hazard ratio, 1.051; 95% CI, 1.007-1.093; p = 0.0243).

CONCLUSIONS

Carbapenem exposure quadrupled the hazards of acquiring A. baumannii even after controlling for severity of illness.

Screening for Gram-negative bacteria: Impact of preanalytical parameters

Screening recommendations for multidrug-resistant Gram-negative bacteria comprise microbiological analyses from rectal swabs. However, essential specifications of the preanalytic steps of such screenings, i.e. the sampling technique, sampling devices and sampling site, are lacking. For standardized and optimum screening conditions these parameters are indispensable. Here, the optimum parameters were examined irrespective of the antibiotic resistance patterns of the target bacteria in order to establish a general basis for this type of screening. Swabs with rayon, polyurethane-cellular-foam and nylon-flocked tips were tested. Different sampling locations were evaluated, i.e. perianal, intraanal and deep intraanal. Subjects were swabbed and quantities of E. coli, K. pneumoniae, P. aeruginosa and A. baumannii were assessed. Overall prevalences of E. coli, K. pneumoniae, P. aeruginosa, and A. baumannii were 94%, 16%, 12%, and 2%, respectively. Bacterial recovery rates were independent from the sampling-timepoint during hospital stay. Polyurethane-cellular-foam or nylon-flocked swabs recovered significantly more bacteria as compared to rayon swabs. Intraanal swabbing resulted in significantly higher bacterial quantities as compared to perianal swabbing. In contrast, for the detection of A. baumannii, perianal swabbing seems more suitable than intraanal swabbing. Gender-related differences in bacterial recovery could be detected from perianal but not from intraanal swabs.

Research Methods in Healthcare Epidemiology and Antimicrobial Stewardship-Observational Studies

Observational studies compare outcomes among subjects with and without an exposure of interest, without intervention from study investigators. Observational studies can be designed as a prospective or retrospective cohort study or as a case-control study. In healthcare epidemiology, these observational studies often take advantage of existing healthcare databases, making them more cost-effective than clinical trials and allowing analyses of rare outcomes. This paper addresses the importance of selecting a well-defined study population, highlights key considerations for study design, and offers potential solutions including biostatistical tools that are applicable to observational study designs. Infect Control Hosp Epidemiol 2016;1-6.

Antibiotic-Induced Within-Host Resistance Development of Gram-Negative Bacteria in Patients Receiving Selective Decontamination or Standard Care

OBJECTIVE

To quantify antibiotic-associated within-host antibiotic resistance acquisition rates in Pseudomonas aeruginosa, Klebsiella species, and Enterobacter species from lower respiratory tract samples of ICU patients receiving selective digestive decontamination, selective oropharyngeal decontamination, or standard care.

DESIGN

Prospective cohort.

SETTING

This study was nested within a cluster-randomized crossover study of selective digestive decontamination and selective oropharyngeal decontamination in 16 ICUs in The Netherlands.

PATIENTS

Eligible patients were those colonized in the respiratory tract with P. aeruginosa, Klebsiella species, or Enterobacter species susceptible to one of the marker antibiotics and with at least two subsequent microbiological culture results from respiratory tract samples available.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Antibiotic resistance acquisition rates were defined as the number of conversions from susceptible to resistant for a specific antibiotic per 100 patient-days or 100 days of antibiotic exposure within an individual patient. The hazard of antibiotic use for resistance development in P. aeruginosa was based on time-dependent Cox regression analysis. Findings of this study cohort were compared with those of a previous cohort of patients not receiving selective digestive decontamination/selective oropharyngeal decontamination. Numbers of eligible patients were 277 for P. aeruginosa, 174 for Klebsiella species, and 106 for Enterobacter species. Resistance acquisition rates per 100 patient-days ranged from 0.2 (for colistin and ceftazidime in P. aeruginosa and for carbapenems in Klebsiella species) to 3.0 (for piperacillin-tazobactam in P. aeruginosa and Enterobacter species). For P. aeruginosa, the acquisition rates per 100 days of antibiotic exposure ranged from 1.4 for colistin to 4.9 for piperacillin-tazobactam. Acquisition rates were comparable for patients receiving selective digestive decontamination/selective oropharyngeal decontamination and those receiving standard care. Carbapenem exposure had the strongest association with resistance development (adjusted hazard ratio, 4.2; 95% CI, 1.1-15.6).

CONCLUSION

Within-host antibiotic resistance acquisition rates for systemically administered antibiotics were comparable between patients receiving selective decontamination and those receiving standard care and were highest during carbapenem use.

Antimicrobial potentials of Helicteres isora silver nanoparticles against extensively drug-resistant (XDR) clinical isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a leading opportunistic pathogen and its expanding drug resistance is a growing menace to public health. Its ubiquitous nature and multiple resistance mechanisms make it a difficult target for antimicrobial chemotherapy and require a fresh approach for developing new antimicrobial agents against it. The broad-spectrum antibacterial effects of silver nanoparticles (SNPs) make them an excellent candidate for use in the medical field. However, attempts made to check their potency against extensively drug-resistant (XDR) microbes are meager. This study describes the biosynthesis and biostabilization of SNPs by Helicteres isora aqueous fruit extract and their characterization by ultraviolet-visible spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray diffraction, and Fourier transform infrared spectroscopy. Majority of SNPs synthesized were of 8--20-nm size. SNPs exhibited dose-dependent antibacterial activities against four XDR P. aeruginosa (XDR-PA) clinical isolates as revealed by growth curves, with a minimum inhibitory concentration of 300 μg/ml. The SNPs exhibited antimicrobial activity against all strains, with maximum zone of inhibition (16.4 mm) in XRD-PA-2 at 1000 μg/ml. Amongst four strains, their susceptibilities to SNPs were in the following order: XDR-PA-2 > XDR-PA-4 > XDR-PA-3 > XDR-PA-1. The exposure of bacterial cells to 300 μg/ml SNPs resulted into a substantial leakage of reducing sugars and proteins, inactivation of respiratory chain dehydrogenases, and eventual cell death. SNPs also induced lipid peroxidation, a possible underlying factor to membrane porosity. The effects were more pronounced in XDR-PA-2 which may be correlated with its higher susceptibility to SNPs. These results are indicative of SNP-induced turbulence of membranous permeability as an important causal factor in XDR-PA growth inhibition and death.

The role of systemic antibiotics in acquiring respiratory tract colonization with gram-negative bacteria in intensive care patients: a nested cohort study

OBJECTIVE

Colonization of the respiratory tract with Gram-negative bacteria in intensive care patients increases the risk of subsequent infections. Application of systemic antibiotics may prevent colonization with Gram-negative bacteria, but this effect has never been quantified. The objective of this study was to determine associations between systemic antibiotic use and acquisition of respiratory tract colonization with Gram-negative bacteria in ICUs.

DESIGN

A nested cohort study.

SETTING

A university hospital and a teaching hospital.

PATIENTS

Patients with ICU stay of more than 48 hours and absence of respiratory tract colonization with Gram-negative bacteria on ICU admission.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Acquisition was determined through protocolized surveillance. Associations were investigated with Cox regression models with antibiotics as a time-dependent covariate. In all, 250 of 481 patients (52%) acquired respiratory tract colonization with Gram-negative bacteria after a median of 5 days (interquartile range, 3-8 d) (acquisition rate, 77.1/1,000 patient-days at risk). Antibiotic exposure during ICU admission was present in 78% and 72% of the patients with and without acquired Gram-negative bacteria colonization, respectively. In Kaplan-Meier curve analysis, the median times to acquisition of Gram-negative bacteria were 9 days (95% CI, 7.9-10.1) and 6 days (95% CI, 4.8-7.2) in patients receiving and not receiving antibiotics, respectively. In time varying Cox regression analysis, however, the association between acquired colonization and systemic antibiotics was not statistically significant (hazard ratio, 0.90; 95% CI, 0.70-1.16).

CONCLUSIONS

Among patients not colonized with Gram-negative bacteria in the respiratory tract at admission to ICU, systemic antibiotics during ICU stay were not associated with a reduction in acquisition of Gram-negative bacteria carriage in the respiratory tract during the ICU stay.

Acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill medical patients: role of colonization pressure and antibiotic exposure

INTRODUCTION

The objective of this work was to investigate the risk factors for the acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill patients, taking into account colonization pressure.

METHODS

We conducted a prospective cohort study in an 8-bed medical intensive care unit during a 35-month period. Nasopharyngeal and rectal swabs and respiratory secretions were obtained within 48 hours of admission and thrice weekly thereafter. During the study, a policy of consecutive mixing and cycling periods of three classes of antipseudomonal antibiotics was followed in the unit.

RESULTS

Of 850 patients admitted for ≥ 3 days, 751 (88.3%) received an antibiotic, 562 of which (66.1%) were antipseudomonal antibiotics. A total of 68 patients (8%) carried P. aeruginosa upon admission, and among the remaining 782, 104 (13%) acquired at least one strain of P. aeruginosa during their stay. Multivariate analysis selected shock (odds ratio (OR) = 2.1; 95% confidence interval (CI), 1.2 to 3.7), intubation (OR = 3.6; 95% CI, 1.7 to 7.5), enteral nutrition (OR = 3.6; 95% CI, 1.8 to 7.6), parenteral nutrition (OR = 3.9; 95% CI, 1.6 to 9.6), tracheostomy (OR = 4.4; 95% CI, 2.3 to 8.3) and colonization pressure >0.43 (OR = 4; 95% CI, 1.2 to 5) as independently associated with the acquisition of P. aeruginosa, whereas exposure to fluoroquinolones for >3 days (OR = 0.4; 95% CI, 0.2 to 0.8) was protective. In the whole series, prior exposure to carbapenems was independently associated with carbapenem resistance, and prior amikacin use predicted piperacillin-tazobactam, fluoroquinolone and multiple-drug resistance.

CONCLUSIONS

In critical care settings with a high rate of antibiotic use, colonization pressure and non-antibiotic exposures may be the crucial factors for P. aeruginosa acquisition, whereas fluoroquinolones may actually decrease its likelihood. For the acquisition of strains resistant to piperacillin-tazobactam, fluoroquinolones and multiple drugs, exposure to amikacin may be more relevant than previously recognized.

Multidrug-resistant Pseudomonas aeruginosa infections pose growing threat to health care-associated infection control in the hospitals of Southern China: a case-control surveillance study

BACKGROUND

Multidrug-resistant Pseudomonas aeruginosa (MDRPA) is one of the most common agents among health care-associated infections. There is a lack of data on the clinical features of MDRPA from Southern China.

METHODS

A case-control surveillance study of P aeruginosa was conducted based on surveillance from July 2008-December 2012, in 5 hospitals of Guangzhou, China. Data were analyzed by univariate analysis and multivariate logistic regression using Stata 13 (StataCorp, College Station, TX).

RESULTS

Of the 348 P aeruginosa strains, the prevalence of MDRPA was 54%, and it has increased over time. Isolates of P aeruginosa showed increased resistance to most antimicrobials during this time period. Independent risk factors were tracheal intubation insertion (odds ratio [OR], 2.21; 95% confidence interval [CI], 1.16-4.23; P = .02) and use of carbapenem (odds ratio [OR], 3.36; 95% confidence interval [CI], 1.75-6.47; P < .01). The distribution of MDRPA infections was uneven among the 5 hospitals (P = .01). Being infected with MDRPA strains resulted in longer duration of hospitalization (39 vs 24 days) and higher mortality (49% vs 20%).

CONCLUSION

The infections of MDRPA were severe issues. More stringent measures should be applied for those with independent predictors of MDRPA infections because they may induce adverse clinical outcomes.

Assessment of panobacumab as adjunctive immunotherapy for the treatment of nosocomial Pseudomonas aeruginosa pneumonia

The fully human anti-lipopolysaccharide (LPS) immunoglobulin M (IgM) monoclonal antibody panobacumab was developed as an adjunctive immunotherapy for the treatment of O11 serotype Pseudomonas aeruginosa infections. We evaluated the potential clinical efficacy of panobacumab in the treatment of nosocomial pneumonia. We performed a post-hoc analysis of a multicenter phase IIa trial (NCT00851435) designed to prospectively evaluate the safety and pharmacokinetics of panobacumab. Patients treated with panobacumab (n = 17), including 13 patients receiving the full treatment (three doses of 1.2 mg/kg), were compared to 14 patients who did not receive the antibody. Overall, the 17 patients receiving panobacumab were more ill. They were an average of 72 years old [interquartile range (IQR): 64-79] versus an average of 50 years old (IQR: 30-73) (p = 0.024) and had Acute Physiology and Chronic Health Evaluation II (APACHE II) scores of 17 (IQR: 16-22) versus 15 (IQR: 10-19) (p = 0.043). Adjunctive immunotherapy resulted in an improved clinical outcome in the group receiving the full three-course panobacumab treatment, with a resolution rate of 85 % (11/13) versus 64 % (9/14) (p = 0.048). The Kaplan-Meier survival curve showed a statistically significantly shorter time to clinical resolution in this group of patients (8.0 [IQR: 7.0-11.5] versus 18.5 [IQR: 8-30] days in those who did not receive the antibody; p = 0.004). Panobacumab adjunctive immunotherapy may improve clinical outcome in a shorter time if patients receive the full treatment (three doses). These preliminary results suggest that passive immunotherapy targeting LPS may be a complementary strategy for the treatment of nosocomial O11 P. aeruginosa pneumonia.

Risk factors for carbapenem-resistant Gram-negative bacteremia in intensive care unit patients

PURPOSE

Carbapenem-resistant (CR) Gram-negative pathogens have increased substantially. This study was performed to identify the risk factors for development of CR Gram-negative bacteremia (GNB) in intensive care unit (ICU) patients.

METHODS

Prospective study; risk factors for development of CR-GNB were investigated using two groups of case patients: the first group consisted of patients who acquired carbapenem susceptible (CS) GNB and the second group included patients with CR-GNB. Both case groups were compared to a shared control group defined as patients without bacteremia, hospitalized in the ICU during the same period.

RESULTS

Eighty-five patients with CR- and 84 patients with CS-GNB were compared to 630 control patients, without bacteremia. Presence of VAP (OR 7.59, 95 % CI 4.54-12.69, p < 0.001) and additional intravascular devices (OR 3.69, 95 % CI 2.20-6.20, p < 0.001) were independently associated with CR-GNB. Presence of VAP (OR 2.93, 95 % CI 1.74-4.93, p < 0.001), presence of additional intravascular devices (OR 2.10, 95 % CI 1.23-3.60, p = 0.007) and SOFA score on ICU admission (OR 1.11, 95 % CI 1.03-1.20, p = 0.006) were independently associated with CS-GNB. The duration of exposure to carbapenems (OR 1.079, 95 % CI 1.022-1.139, p = 0.006) and colistin (OR 1.113, 95 % CI 1.046-1.184, p = 0.001) were independent risk factors for acquisition of CR-GNB. When the source of bacteremia was other than VAP, previous administration of carbapenems was the only factor related with the development of CR-GNB (OR 1.086, 95 % CI 1.003-1.177, p = 0.042).

CONCLUSIONS

Among ICU patients, VAP development and the presence of additional intravascular devices were the major risk factors for CR-GNB. In the absence of VAP, prior use of carbapenems was the only factor independently related to carbapenem resistance.

Antimicrobial agent exposure and the emergence and spread of resistant microorganisms: issues associated with study design

Antibiotics are essential agents that have greatly reduced human mortality due to infectious diseases. Their use, and sometimes overuse, have increased over the past several decades in humans, veterinary medicine and agriculture. However, the emergence of resistant pathogens is becoming an increasing problem that could result in the re-emergence of infectious diseases. Antibiotic prescription in human medicine plays a key role in this phenomenon. Under selection pressure, resistance can emerge in the commensal flora of treated individuals and disseminate to others. However, even if the effects of antimicrobial use on resistance is intuitively accepted, scientific rationales are required to convince physicians, legislators and public opinion to adopt appropriate behaviours and policies. With this review, we aim to provide an overview of different epidemiological study designs that are used to study the relationship between antibiotic use and the emergence and spread of resistance, as well as highlight their main strengths and weaknesses.

Colistin resistance in gram-negative bacteria during prophylactic topical colistin use in intensive care units

PURPOSE

Topical use of colistin as part of selective digestive decontamination (SDD) and selective oropharyngeal decontamination (SOD) has been associated with improved patient outcome in intensive care units (ICU), yet little is known about the risks of colistin resistance. We quantified effects of selective decontamination on acquisition of colistin-resistant gram-negative bacteria (GNB) using data from a cluster-randomized study and a single-centre cohort.

METHODS

Acquisition of colistin-resistant GNB and conversion from susceptible to resistance in GNB was determined in respiratory samples [from patients receiving SDD (n = 455), SOD (n = 476), or standard care (SC) (n = 315)], and in rectal swabs from 1,840 SDD-patients. Genotyping of converting isolates was performed where possible.

RESULTS

The respiratory tract acquisition rates of colistin-resistant GNB were comparable during SDD, SOD, and SC and ranged from 0.7 to 1.1/1,000 patient-days at risk. Rectal acquisition rates during SDD were <3.3/1,000 days at risk. In patients with respiratory tract GNB carriage, conversion rates were 3.6 and 1.1/1,000 patient-days at risk during SDD and SC, respectively, (p > 0.05). In patients with rectal GNB carriage conversion rates during SDD were 5.4 and 3.2/1,000 days at risk and 15.5 and 12.6/1,000 days at risk when colonized with tobramycin-resistant GNB.

CONCLUSIONS

Acquisition rates with colistin-resistant GNB in the respiratory tract were low and comparable with and without topical use of colistin. Rates of acquisition of colistin-resistant GNB during SDD were--in ICUs with low endemicity of antibiotic resistance--<2.5/1,000 days at risk, but were fivefold higher during persistent GNB colonization and 15-fold higher during carriage with tobramycin-resistant GNB.