Invasive Pseudomonas aeruginosa infections: high rate of recurrence and mortality after hematopoietic cell transplantation

Mortality after bloodstream infections in allogeneic haematopoietic stem cell transplant (HSCT) recipients

PURPOSE

Bloodstream infections (BSIs) are frequent after allogeneic haematopoietic stem cell transplantation (HSCT). The aim of this study was to identify predictors of mortality after BSI in patients who undergo HSCT.

METHODS

Patients who underwent HSCT between 1 January 2004 and 31 January 2008 and developed BSI during the first year post-transplantation were included. Variables influencing overall mortality at 7 and 30 days after BSI were analysed.

RESULTS

BSIs developed in 149 patients, within a median of 9 days after undergoing HSCT. Early and late mortality were 15 and 27%, respectively. Of the BSI, 54% were due to Gram-positive microorganisms, 33% were due to Gram-negative microogranisms, 10% were polymicrobial and 3% were fungal. The associated 7-and 30-day mortality was respectively 10 and 24% (Gram positive), 22 and 31% (Gram negative; Pseudomonas aeruginosa mortality 67%, all within 7 days), 13 and 27% (polymicrobial) and 40% (fungal, all within 7 days). Early mortality was higher in relapsed disease at HSCT (25.9%, p = 0.01), but lower in early (i.e. within 20 days of HSCT) BSI (11.7%, p = 0.03) and BSI due to Gram-positive infective agents (10%, p = 0.05). Multivariate analysis confirmed a higher mortality in late BSI [odds ratio (OR) 3.29, p = 0.03] and relapsed disease at HSCT (OR 2.2, p = 0.04). Late mortality was associated with the type of underlying disease (OR 0.44 for diseases other than acute leukaemia, p = 0.05) and its status (OR 6.04 for relapse at HSCT, p = 0.001). Appropriate empirical therapy was associated with lower early and late mortality in single Gram-negative BSI (16 vs. 45% for 7-day mortality, p = 0.09; 21 vs. 64% for 30-day mortality, p = 0.02).

CONCLUSIONS

BSIs are frequent during the first year after HSCT and are associated with a high mortality rate. The aetiology influenced early mortality, while the type and phase of the underlying disease played a pivotal role in late mortality. Appropriate empirical therapy is crucial in BSI due to Gram-negative infective agents.

Molecular epidemiology of a Pseudomonas aeruginosa hospital outbreak driven by a contaminated disinfectant-soap dispenser

BACKGROUND AND OBJECTIVE

Pseudomonas aeruginosa infection represents a main cause of morbidity and mortality among immunocompromised patients. This study describes a fatal epidemic of P. aeruginosa that occurred in a hematology unit in Italy.

METHODS

Retrospective cohort study, prospective surveillance, auditing, extensive testing on healthcare workers and environmental investigation were performed to define the dynamics and potential causes of transmission. RAPD, macrorestriction analyses and sequence typing were used to define relationships between P. aeruginosa isolates.

RESULTS

Eighteen cases of infection were identified in the different phases of the investigation. Of these, five constitute a significant molecular cluster of infection. A P. aeruginosa strain with the same genetic fingerprint and sequence type (ST175) as clinical isolates strain was also isolated from a heavily contaminated triclosan soap dispenser.

DISCUSSION AND CONCLUSIONS

Our results are consistent with the hypothesis that patients became indirectly infected, e.g., during central venous catheter handling through contaminated items, and that the triclosan soap dispenser acted as a common continuous source of P. aeruginosa infection. Since P. aeruginosa is intrinsically unsusceptible to triclosan, the use of triclosan-based disinfectant formulations should be avoided in those healthcare settings hosting patients at high risk of P. aeruginosa infection.

High-dose continuous infusion beta-lactam antibiotics for the treatment of resistant Pseudomonas aeruginosa infections in immunocompromised patients

OBJECTIVE

To report a case series of high-dose continuous infusion beta-lactam antibiotics for the treatment of resistant Pseudomonas aeruginosa infections.

CASE SUMMARY

Continuous infusion ceftazidime or aztreonam was administered to achieve target drug concentrations at or above the minimum inhibitory concentration, when possible, in 3 patients with P. aeruginosa infections. The maximal calculated target drug concentration was 100 mg/L. In the first patient, with primary immunodeficiency, neutropenia, and aggressive cutaneous T-cell lymphoma/leukemia, continuous infusion ceftazidime (6.5-9.6 g/day) was used to successfully treat multidrug-resistant P. aeruginosa bacteremia. In the second patient, with leukocyte adhesion deficiency type 1, continuous infusion aztreonam (8.4 g/day) was used to successfully treat multidrug-resistant P. aeruginosa wound infections. In the third patient, with severe aplastic anemia, continuous infusion ceftazidime (7-16.8 g/day) was used to treat P. aeruginosa pneumonia and bacteremia. In each patient, bacteremia cleared, infected wounds healed, and pneumonia improved in response to continuous infusion ceftazidime or aztreonam.

DISCUSSION

Treatment strategies for multidrug-resistant P. aeruginosa infections are limited. A novel treatment strategy, when no other options are available, is the continuous infusion of existing beta-lactam antibiotics to maximize their pharmacodynamic activity. High-dose continuous infusion ceftazidime or aztreonam was used for the successful treatment of resistant systemic P. aeruginosa infections in 3 chronically immunocompromised patients.

CONCLUSIONS

Continuous infusion beta-lactam antibiotics are a potentially useful treatment strategy for resistant P. aeruginosa infections in immunocompromised patients.

Multidrug resistant Pseudomonas aeruginosa infection in children undergoing chemotherapy and hematopoietic stem cell transplantation

Pseudomonas aeruginosa is one leading gram-negative organism associated with nosocomial infections. Bacteremia is life-threatening in the immunocompromised host. Increasing frequency of multi-drug-resistant (MDRPA) strains is concerning. We started a retrospective survey in the pediatric hematology oncology Italian network. Between 2000 and 2008, 127 patients with Pseudomonas aeruginosa bacteremia were reported from 12 centers; 31.4% of isolates were MDRPA. Death within 30 days of a positive blood culture occurred in 19.6% (25/127) of total patients; in patients with MDRPA infection it occurred in 35.8% (14/39). In the multivariate analysis, only MDRPA had significant association with infection-related death. This is the largest series of Pseudomonas aeruginosa bacteremia cases from pediatric hematology oncology centers. Monitoring local bacterial isolates epidemiology is mandatory and will allow empiric antibiotic therapy to be tailored to reduce fatalities.

Advances and challenges in infectious diseases supportive care of patients with hematologic malignancies, hematopoietic stem cell transplantation, and severe aplastic anemia

Infectious diseases are important causes of morbidity and mortality in immunocompromised patients with hematological malignancies, severe aplastic anemia (SAA), and myelodysplasia. Major advances in infectious diseases supportive care have been critical to improving the outcome of patients suffering from these life-threatening diseases. Advances in diagnosis, treatment, and prevention of life-threatening infections have reduced morbidity and mortality, improved quality of life, and enabled the use of potentially curative chemotherapy, radiation, hematopoietic stem cell transplantation (HSCT), and immunosuppressive therapy to patients battling these devastating diseases. Despite these advances, the continued development of antimicrobial resistance, emergence of new pathogens, and the evolution of host factors present evolving challenges to the successful management of infectious complications in this expanding patient population.

Pseudomonas aeruginosa eliminates natural killer cells via phagocytosis-induced apoptosis

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes the relapse of illness in immunocompromised patients, leading to prolonged hospitalization, increased medical expense, and death. In this report, we show that PA invades natural killer (NK) cells and induces phagocytosis-induced cell death (PICD) of lymphocytes. In vivo tumor metastasis was augmented by PA infection, with a significant reduction in NK cell number. Adoptive transfer of NK cells mitigated PA-induced metastasis. Internalization of PA into NK cells was observed by transmission electron microscopy. In addition, PA invaded NK cells via phosphoinositide 3-kinase (PI3K) activation, and the phagocytic event led to caspase 9-dependent apoptosis of NK cells. PA-mediated NK cell apoptosis was dependent on activation of mitogen-activated protein (MAP) kinase and the generation of reactive oxygen species (ROS). These data suggest that the phagocytosis of PA by NK cells is a critical event that affects the relapse of diseases in immunocompromised patients, such as those with cancer, and provides important insights into the interactions between PA and NK cells.

Pseudomonas aeruginosa bacteremia over a 10-year period: multidrug resistance and outcomes in transplant recipients

AIM

Transplant recipients are at risk for hospital-acquired infections (HAIs), including those caused by Pseudomonas aeruginosa. Of all HAIs, bloodstream infection (BSI) remains one of the most life-threatening.

METHODS

Over a 10-year period, we studied 503 patients, including 149 transplant recipients, with pseudomonal BSI from the University of Pittsburgh Medical Center. Trends in antimicrobial susceptibility, risk factors for multidrug resistance (MDR), and outcomes were compared between transplant and non-transplant patients.

RESULTS

Resistance to all antibiotic classes was significantly greater in pseudomonal blood culture isolates from transplant compared with non-transplant patients (P<0.001). Of isolates from transplant recipients (n=207), 43% were MDR, compared with 18% of isolates from non-transplant patients (n=391) (odds ratio [OR] 3.47; 95% confidence interval [CI] 2.34-5.14, P<0.001). Among all patients, independent risk factors for MDR P. aeruginosa BSI included previous transplantation (OR 2.38; 95% CI 1.51-3.76, P<0.001), hospital-acquired BSI (OR 2.41; 95% CI 1.39-4.18, P=0.002), and prior intensive care unit (ICU) admission (OR 2.04; 95% CI 1.15-3.63, P=0.015). Mortality among transplant recipients was 42%, compared with 32% in non-transplant patients (OR 1.55; 95% CI 0.87-2.76, P=0.108). For transplant recipients, onset of BSI in the ICU was the only independent predictor of mortality (OR 8.00; 95% CI 1.71-37.42, P=0.008).

CONCLUSIONS

Transplant recipients are at greater risk of MDR P. aeruginosa BSI, with an appreciable mortality. Future management must concentrate on the implementation of effective preventative strategies.

Molecular epidemiological investigation of an outbreak of Pseudomonas aeruginosa infection in an SCT unit

From May to October 2006, six severe Pseudomonas aeruginosa infections were diagnosed in patients undergoing SCT in the SCT unit of the Careggi hospital (Florence, Italy). Four of the infected patients were treated consecutively in the same room (room N). On the hypothesis of a possible environmental source of infection, samples were collected from different sites that had potential for cross-contamination throughout the SCT unit, including the electrolytic chloroxidant disinfectant used for hand washing (Irgasan) and the disinfectant used for facilities cleaning. Four of the environmental samples were positive for P. aeruginosa: three Irgansan soap samples and a tap swab sample from the staff cleaning and dressing room. The AFLP (amplified fragment length polymorphism) typing method employed to evaluate strain clonality showed that the isolates from the patients who had shared the same room and an isolate from Irgasan soap had a significant molecular similarity (dice index higher than 0.93). After adequate control measures, no subsequent environmental sample proved positive for P. aeruginosa. These data strongly support the hypothesis of the clonal origin of the infective strains and suggest an environmental source of infection. The AFLP method was fast enough to allow a 'real-time' monitoring of the outbreak, permitting additional preventive measures.

Pretransplant neutropenia is associated with poor-risk cytogenetic features and increased infection-related mortality in patients with myelodysplastic syndromes

A retrospective cohort analysis was performed to determine the impact of neutropenia on the outcome of hematopoietic cell transplantation (HSCT) in patients with myelodysplasia (MDS). Among 291 consecutive patients, 178 (61%) had absolute neutrophil counts (ANCs) <1500/microL and 113 (39%) had ANCs > or =1500/microL within 2 weeks before HSCT. Neutropenic patients more often had poor-risk karyotypes (34% versus 12%, P < .0001) and high-risk International Prognostic Scoring System scores (37% versus 18%, P = .0006). After HSCT, the rate of infections caused by Gram-positive bacteria and invasive fungal infections was significantly increased among neutropenic patients (rate ratio [RR] 1.77, P = .02 and RR = 2.56, P = .03, respectively), whereas infections caused by Gram-negative bacteria were not affected (RR 1.33, P = .53). The hazards of nonrelapse mortality (NRM) (hazard ratio [HR] = 1.62 [1.1-2.4], P = .01), overall mortality (HR = 1.55 [1.1-2.1], P = 0.007), and infection-related mortality (HR = 2.22 [1.2-4.2], P = .01) were increased in neutropenic patients, whereas relapse, engraftment, and graft-versus-host-disease were not affected. After adjusting for cytogenetic risk and marrow myeloblast percentages, neutropenic patients remained at significant hazard for infection-related mortality (HR = 1.94 [1.0-3.8], P = .05), but not for overall mortality or NRM. We propose that intensified strategies to prevent infections should be implemented in MDS patients with preexisting neutropenia who undergo HSCT.

A Serious Complication of Allogeneic Stem Cell Transplantation: Relapsing Pseudomonas aeruginosa Panniculitis

A 58-year-old female following an allogeneic stem cell transplant (alloSCT) presented with tender subcutaneous nodule in the axillary and inguinal regions. One of the nodules was biopsied and cultured. The patient was diagnosed with Pseudomonas aeruginosa ( P. aeruginosa) panniculitis. Blood cultures were negative for P. aeruginosa. The patient responded to 4 weeks of imipenem-cilastatin and gentamicin treatment but relapsed immediately after the discontinuation of antibiotic treatment with a change in the susceptibility of P. aeruginosa to antibiotics. The patient received piperacillin-tazobactam and aztreonam with no recurrence for nine months. Differential diagnosis of subcutaneous nodules can be difficult in an alloSCT setting. P. aeruginosa should be kept in mind, and the biopsy and culture of a nodule should be obtained without delay. Blood cultures can be negative. Despite long term antibiotic treatment, relapse can occur.