Investigation of an outbreak of nosocomial infection due to a multiply drug-resistant strain of Pseudomonas aeruginosa

Wide dispersion of ST175 clone despite high genetic diversity of carbapenem-nonsusceptible Pseudomonas aeruginosa clinical strains in 16 Spanish hospitals

During the COMParative Activity of Carbapenems Testing (COMPACT) surveillance study, 448 Pseudomonas aeruginosa clinical isolates were obtained from 16 Spanish hospitals. Nonsusceptibility (EUCAST breakpoints) to imipenem (35%), meropenem (33%), and/or doripenem (33%) was observed with 175 isolates (39%). Simultaneous resistance to these three drugs was observed with 126 of the 175 isolates (72%). Except for colistin, high resistance rates were observed among noncarbapenem antibiotics. Clonal relatedness was investigated by pulsed-field gel electrophoresis (PFGE) with SpeI, discriminating 68 patterns. Multilocus sequence typing (MLST) was performed on 84 isolates representing different PFGE types and all participating hospitals. Thirty-nine sequence types (STs) could be distinguished, and of these, ST175 (48 isolates, 10 hospitals), ST646 (16 isolates, 4 hospitals), ST532 (13 isolates, 3 hospitals), and ST111 (13 isolates, 7 hospitals) were the most frequently encountered. Minimum-spanning tree analysis confirmed a wide dissemination of different clones among participant hospitals, particularly ST175. PFGE pattern comparison within the four most frequent STs revealed that ST175 isolates were relatively uniform, while ST646, ST532, and ST111 isolates were highly diverse, with almost every isolate belonging to a unique pulsotype, even when originating from the same center. The population of carbapenem-nonsusceptible P. aeruginosa isolates from 16 hospitals is highly diverse, with one ST (ST175) representing a highly conserved clone disseminated in 10 of the 16 participant hospitals. This ST175 clone should be added to the list of P. aeruginosa clones at high risk for epidemic spread, such as the Liverpool, Manchester, and Melbourne clones previously found in cystic fibrosis patients and ST235 in the nosocomial setting.

The role of interventional molecular epidemiology in controlling clonal clusters of multidrug resistant Pseudomonas aeruginosa in critically ill cancer patients

BACKGROUND

Pseudomonas aeruginosa is one of the leading causes of hospital-acquired infections in intensive care units (ICUs). The objective was to evaluate the impact of molecular identification of clonal multidrug-resistant (MDR) P aeruginosa strains and the implementation of infection control measures.

METHODS

One hundred seventy-seven strains from ICU patients infected or colonized with MDR P aeruginosa from May 2001 to April 2006 were collected. In vitro susceptibility to 16 antibiotics was done. Pulsed-field gel electrophoresis was performed to identify clonal strains. Nosocomial outbreak was defined as the presence of > or =3 MDR P aeruginosa over < or =3 consecutive months.

RESULTS

During the 5 years of the study, 25 infected and 14 colonized patients with a clonal strain of MDR P aeruginosa were distributed among 5 episodic clusters. These strains were only susceptible to ceftazidime and colistin. Molecular biology identification, diligent monitoring, and multidisciplinary infection control interventions were implemented to suppress this clonal strain after each cluster. Even more, after the last outbreak (June-August 2005), the infection control measures were able to reduce the MDR P aeruginosa to zero during the last 8 months of this study.

CONCLUSION

Interventional molecular epidemiology combined with early identification, monitoring, and implementation of multidisciplinary infection control measures can control temporarily the transmission of MDR P aeruginosa infection in ICUs.

Colistin is effective in treatment of infections caused by multidrug-resistant Pseudomonas aeruginosa in cancer patients

The increasing incidence of infections caused by multidrug-resistant Pseudomonas aeruginosa is a worldwide health problem. Because no new antipseudomonal agents are expected to be available in the near future, we evaluated the safety and efficacy of colistin, an old drug with bactericidal activity against this organism. We collected clinical and demographic data on 95 cancer patients diagnosed with infections caused by multidrug-resistant P. aeruginosa between January 2001 and January 2004 and treated with either colistin (colistin group) or at least one active antipseudomonal agent (a beta-lactam antibiotic or a quinolone) (control group). We compared the results obtained for both groups. Thirty-one patients had been treated with colistin and 64 had been treated with an antipseudomonal non-colistin-containing regimen. Compared with the control group, patients in the colistin group had a lower median age (52 and 62 years, respectively; P = 0.012) but were more likely to have had nosocomial infections (87% and 64%, respectively; P = 0.02). Twenty-five patients (81%) in the colistin group and 40 patients (63%) in the control group had an APACHE II score of >15 (P = 0.074). The overall clinical response rates were 52% in the colistin group and 31% in the control group (P = 0.055). Multiple logistic regression analysis showed that those patients treated with colistin were 2.9 times (95% confidence interval, 1.1 to 7.6 times) more likely than those in the control group to experience a clinical response to therapy (P = 0.026). Colistin therapy was at least as effective and as safe a beta-lactam antibiotic or a quinolone in the treatment of infections caused by multidrug-resistant P. aeruginosa and, hence, may be a useful or preferred alternative therapy for this infection in cancer patients.

Risk factors for the isolation of multi-drug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa: a systematic review of the literature

An understanding of the epidemiology of multi-drug-resistant (MDR) Acinetobacter baumannii and Pseudomonas aeruginosa infections is necessary in order to develop strategies to curtail their spread. For this purpose, the evidence linking the isolation of MDR A. baumannii and P. aeruginosa with specific risk factors was evaluated. PubMed was searched for the 20-year period from September 1985 to September 2005, and eligible studies were considered to be those that: (1) linked the isolation of A. baumannii and P. aeruginosa with specific risk factors; (2) described the characteristics of the affected patients in detail; and (3) provided data on the antibiotic resistance profile of the isolated micro-organisms. Fifty-five studies were found referring to A. baumannii (28 with case-control methodology and 27 outbreak investigations without case-control methodology), and 42 studies were found referring to P. aeruginosa (25 with case-control methodology and 17 outbreak investigations without case-control methodology). Although heterogeneous study designs and investigated risk factors limited this analysis, it was concluded that acquisition and spread of these micro-organisms appear to be related to a large number of variables. Among the most important were deficiencies in the implementation of infection control guidelines and the use of broad-spectrum antibiotics. Use of carbapenems and third-generation cephalosporins appear to be related to the development of an MDR phenotype by A. baumannii, while carbapenems and fluoroquinolones are implicated in MDR P. aeruginosa. The diversity of risk factors associated with the development of MDR A. baumannii and P. aeruginosa suggests that a separate outbreak investigation should be performed in each hospital setting. The development of innovative control strategies is needed in order to limit the spread of these pathogens.

Risk factors for infections with multidrug-resistantPseudomonas aeruginosa in patients with cancer

BACKGROUND

Pseudomonas aeruginosa is responsible for a wide range of infections. In immunocompromised patients with cancer, the emergence of multidrug resistant P. aeruginosa may have grave consequences.

METHODS

Patients with cancer who were infected with multidrug-resistant P. aeruginosa with polyclonal DNA restriction patterns were used as the case group. Two control groups were used: one group of cancer patients who were infected with multidrug-susceptible P. aeruginosa and another group of cancer patients who had the same underlying disease and the same intensive care unit exposure as patients in the case group but who were not infected or colonized by P. aeruginosa.

RESULTS

Risk factors that were associated significantly with multidrug-resistant P. aeruginosa infection were the use of carbapenem for > or = 7 days, a history of P. aeruginosa infection during the preceding year, and a history of chronic obstructive pulmonary disease (P < 0.01).

CONCLUSIONS

Carbapenems may need to be used more judiciously as first-line empirical therapy for cancer patients with prior pseudomonal infection or chronic obstructive pulmonary disease who require hospitalization, and alternative, antipseudomonal antibiotic regimens may need to be considered, especially in this patient population.

Multidrug-resistant Pseudomonas aeruginosa isolated from the urine of patients with urinary tract infection

We report the clinical courses of 3 patients with urinary obstruction who developed acute pyelonephritis caused by multidrug-resistant (MDR) Pseudomonas aeruginosa. Genome fingerprinting was performed to clarify the route of cross-infection, and an imipenem-resistance gene was detected by the polymerase chain reaction (PCR) method. The study included 17 patients at our institute who had urinary tract infections caused by P. aeruginosa between January and December 1997. MDR was defined as that when all the minimum inhibitory concentrations (MICs) were determined to show resistance according to the breakpoints recommended by the National Committee for Clinical Laboratory Standards (NCCLS) for P. aeruginosa. Pulse-field gel electrophoresis (PFGE) was carried out for genome fingerprinting. PCR was used to detect the metallo-beta-lactamase gene ( bla(IMP)). Three strains were revealed for MDR. The strains were isolated from the 3 patients with urinary tract obstruction who developed acute pyelonephritis. The treatment consisted of urinary drainage for the obstructed urinary tract and parenterally administered antimicrobials. Although none of the strains was susceptible to any antimicrobials, all patients had favorable outcomes. PFGE revealed that two strains had an identical genotype, implying cross-infection between the patients. The bla(IMP) gene was not detected in any of the three strains. In febrile patients with urinary tract infection caused by MDR P. aeruginosa, treatment for urinary obstruction is strongly recommended. Initial empirical chemotherapy with antimicrobials to which the organism is not susceptible is often inevitable. Because there was epidemiological evidence of cross-infection with MDR P. aeruginosa, countermeasures against nosocominal infection are warranted.

Multiresistant Pseudomonas aeruginosa outbreak in a pediatric oncology ward related to bath toys

BACKGROUND

Nosocomial outbreaks of Pseudomonas aeruginosa in pediatric hospitals frequently involve neonates and immunosuppressed patients and can cause significant morbidity and mortality.

OBJECTIVE

To describe the investigation of a multidrug-resistant P. aeruginosa outbreak in a pediatric oncology ward at the Royal Children's Hospital, Melbourne, Australia.

DESIGN AND METHODS

Specimens were collected from infected patients and the ward environment. Bacterial isolates were characterized by antibiotic susceptibility patterns and bacterial DNA fingerprinting performed by pulsed-field gel electrophoresis (PFGE). A case-control study was carried out to assess possible risk factors for infection.

RESULTS

Eight patients had clinical illnesses including bacteremia (n = 5) and infections of skin (n = 2), central venous catheter site (n = 1) and urinary tract (n = 1). The environmental ward survey yielded isolates of multiresistant P. aeruginosa from a toy box containing water-retaining bath toys, as well as from three of these toys. Pulsed-field gel electrophoresis of bacterial DNA demonstrated identical band patterns of the isolates from patients, toys and toy box water. A case-control study involving the 8 cases and 24 disease-matched controls demonstrated a significant association between P. aeruginosa infection and use of bath toys (P = 0.004), use of bubble bath (P = 0.014), duration of stay (P = 0.007) and previous antibiotic exposure (P = 0.026). Cultures from the bubble bath liquid were negative.

CONCLUSION

This is the first description of a nosocomial outbreak associated with toys. We caution against the use of water-retaining bath toys in wards treating immunocompromised children.

Outbreak of gentamicin, ciprofloxacin-resistant Pseudomonas aeruginosa in an intensive care unit, traced to contaminated quivers

An outbreak of gentamicin, ciprofloxacin-resistant Pseudomonas aeruginosa in an intensive care unit, was investigated. The majority of isolates were from sputum and the organism was not isolated from any other patient in the hospital, except those admitted to the unit. A prospective study was set up, and the organism was found to be associated with contaminated quivers, used to store suction tubing between use on ventilated patients. Once the quivers were disinfected and changed between patients daily, the outbreak stopped. Suction of ventilated patients may be an important source of contamination of the respiratory tract with nosocomial pathogens. It is important that infection control teams regularly review procedures to ensure the correct practices are being followed, so that nosocomial outbreaks of infection may be prevented.