An Outbreak of Gentamicin-ResistantEnterobacter cloacaeInfections in a Pediatric Intensive Care Unit

Controlling healthcare-associated infections: the role of infection control and antimicrobial use practices

Healthcare-associated infections are a major cause of morbidity and mortality in pediatric patients in the United States and throughout the world. Overall rates of infection range widely depending on the pediatric population, with the highest rates being in patients in neonatal intensive care units, followed by those in pediatric intensive care units, immunocompromised patients, and those undergoing surgical procedures. Risk factors for healthcare-associated infection include intrinsic and extrinsic factors. The major intrinsic factors are age, birth weight, underlying diseases, and immune status. The major extrinsic factors are presence of invasive devices and procedures. The major risk factors for healthcare-associated infection caused by antimicrobial-resistant pathogens are either the transmission of pathogens from person to person (directly or indirectly, usually via the hands of healthcare workers) or the emergence of resistance after exposure to antimicrobials. Preventing healthcare-associated infections caused by antimicrobial-resistant pathogens requires a comprehensive approach that includes: 1) preventing infections through the use of vaccines and prophylaxis; 2) minimizing the use of invasive devices; 3) understanding and fully implementing (and complying with) current guideline recommendations for the prevention of infections; and 4) using antimicrobials judiciously. Implementing such a comprehensive program will reduce healthcare-associated infections, reduce the prevalence of antimicrobial-resistant pathogens, improve patient outcomes, and reduce health care costs.

Outbreak investigation of nosocomial enterobacter cloacae bacteraemia in a neonatal intensive care unit

Over a period of 7 months, 23 patients hospitalized in a neonatal intensive care unit (NICU) developed nosocomial Enterobacter cloacae bacteraemia. Contaminated saline for preparing heparin solution was initially identified as the common source of E. cloacae bacteraemia. Although environmental sanitation was enforced, the outbreak continued. E. cloacae has always been isolated from various cultures of the environmental specimens, from the hands of personnel and from the faeces of patients. All of the 23 bacteraemic isolates and 8 stool isolates from infected infants, as well as the 17 isolates from environmental specimens were found to be of the same genotype using the polymerase chain reaction-based DNA fingerprinting method. After various infection control methods were instituted, the outbreak eventually came under control. For epidemiological investigation, 23 neonates without E. cloacae bacteraemia were matched for case-control study. Nineteen (83%) of the case-patients were premature. The significant risk factors leading to E. cloacae bacteraemia in the NICU included small gestation age, low birthweight, exposure to personnel with contaminated hands and the presence of E. cloacae in the stool carriage (p=0.003, 0.007, 0.018 and 0.040, respectively). The gastrointestinal tracts of the patients and environmental surfaces appeared to be the principal sites of bacterial reservoir. In conclusion, the outbreak of E. cloacae bacteraemia was caused by a particular strain and possibly via multiple modes of transmission, including a bottle of contaminated saline as an initial common source, endogenous spread from the gastrointestinal tract and successive cross-infections between patients, hands of personnel and the environment. Effective infection control requires a multidisciplinary approach and reinforcement of infection control procedures, including aseptic technique, hand washing, proper isolation and disinfection of environmental surfaces.

Enterobacter cloacae outbreak in the NICU related to disinfected thermometers

In the first week ot December 1997, an increasing incidence of neonates colonized with multi-drug resistant Enterobacter cloacae (MR-E. cloacae) was observed in the neonatal Intensive care unit of our 950-bed university hospital. Initially, re-enforcement of infection control practices including hand disinfection and cohort isolation seemed to be sufficient to control the outbreak. Nevertheless, an increasing number of newly admitted patients was paralleled by another rise in the incidence of colonized neonates. Since E. cloacae was initially found in urine specimens of the patients, surveillance and environmental cultures were aimed at procedures and instruments that might colonize the gastro-intestinal and/or urinary tract. E, cloacae was isolated from a single cap of an electronic digital thermometer. Despite banning of this possible source, newly admitted neonates still became colonized. The unit was closed for further admissions and a second round of extensive screening was started; this time including all available thermometers and continuous rectal temperature probes. Ready-to-use 'disinfected thermometers and probes were found to be colonized with MR-E. cloacae. Observation of disinfection procedures and a laboratory investigation revealed that 'rushed disinfection with alcohol 80% led to a 1 in 10 chance of thermometers still being contaminated. Furthermore, alcoholic hand rub used for convenience disinfection failed to disinfect thermometers in 40% and 20% of the cases when done in a 'rushed' or 'careful' fashion, respectively. Adequate disinfection of the thermometers led to the control of the outbreak, with no new occurrence of MR-E. cloacae in the following months.

The effect of new disinfectant substances on the metabolism of Enterobacter cloacae

The antimicrobial mechanism of 16 new commercially manufactured disinfectant substances on an Enterobacter cloacae strain was studied. The substances tested represent 11 quaternary ammonium salts (QAS) and five combinated QAS with other ingredients. The antimicrobial efficacy was characterized by influencing the growth of bacterial cells expressed by MIC and ED50 values as well as by the inhibition of the incorporation rate of [14C] adenine and [14C] leucine. The disinfectants are divided into three groups according to their efficacy. The first group comprised substances with strong inhibitory effect (MIC 0.006-0.048 mg l(-1)) such as triquart, topax 91, benzalkonium chloride, neoquat S, ID 213, and antibacteric P. The second group represented substances with good antibacterial efficacy (MIC 0.048-0.15 mg l(-1)), and the third group were substances with MIC values up to 0.195-0.39 mg l(-1). Cetrimide had low activity (MIC 3.12-6.25 mg l(-1)). The effect of substances studied on the biosynthetic processes expressed by R values (IC50 Ade:IC50 Leu) showed that these values were < 1 except ADL 007. Much lower IC50 Ade and IC50 Leu values of the disinfectant substances studied suggested interference of these substances with nucleic acid synthesis and proteins synthesis which was expressed by inhibition of both precursors. All substances except cetrimide caused an inhibition of the endogenous respiration. The highest inhibition was caused by benzalkonium chloride. This affected the respiration significantly in the presence of intermediators of the Krebs' cycle (glycerol, aspartate). The tested substance suppressed the growth of E. cloacae probably through interference with energy-yielding and energy-requiring processes of the cells.

Enterobacter spp.: pathogens poised to flourish at the turn of the century

Knowledge of the genus Enterobacter and its role in human disease has expanded exponentially in recent years. The incidence of infection in the hospital and the community has increased. New clinical syndromes have been recognized. Enterobacter spp. have also been implicated as causes of other syndromes that traditionally have been associated almost exclusively with more easily treatable pathogens, such as group A streptococci and staphylococci. Rapid emergence of multiple-drug resistance has been documented in individual patients during therapy and in populations and environments with strong selective pressure from antimicrobial agents, especially the cephalosporins. Therapeutic options for patients infected with multiply resistant strains have become severely limited. Carbapenems or, alternatively, fluoroquinolones are the most predictively active options, although resistance to both classes has been observed on rare occasions. Enterobacter spp. appear well adapted for survival and even proliferation as the turn of the century approaches.

Clinical and bacteriological survey after change in aminoglycoside treatment to control an epidemic of Enterobacter cloacae

The effect of a change in the first line antibiotic treatment in a neonatal unit was studied. A total of 238 neonates (G1), admitted between 1 January and 31 July 1989, and treated with gentamicin, were compared with 398 (G2) admitted between 1 August 1989 and 31 July 1990 who received amikacin, in the combination of ampicillin plus an aminoglycoside. This change was implemented in an attempt to prevent the spread of an epidemic strain of Enterobacter cloacae resistant to third generation cephalosporins and all aminoglycosides, except amikacin. The change in treatment had no effect on the incidence of nosocomial infections [19.7% (G1) vs. 16.3% (G2) RR = 1.21 (0.86-1.70)], but the proportion of patients with nosocomial infections caused by the E. cloacae decreased (6.3% vs. 2.0% RR 3.14 CI 1.35-7.28). Certain trends in the bacterial ecology emerged: E. aerogenes and Enterococci increased in G2. The proportion of gentamicin-resistant strains such as E. cloacae or Staphylococci decreased and there was no increase in aminoglycoside-resistant strains, except in Escherichia coli, in which resistance to amikacin rose from 0 to 3%. This study illustrates the influence of antimicrobial therapy on the species and the resistance of strains isolated in nosocomial infections. It also highlights the need for epidemiologic surveillance, and poses the question of how best to modify antibiotic policy.

Biotyping, phage typing, and O-serotyping of clinical isolates of Enterobacter cloacae

The purpose of this study was to make an independent evaluation of the methods of bio-, phage-, and O-serotyping which had been used only in the laboratory of origin, and to assess the extent of possible cross-infection of Enterobacter cloacae in a Danish university hospital. The material consisted of 237 clinical isolates of E. cloacae from the clinical microbiology laboratory at Hvidovre Hospital. The typability of bio-, phage-, and serotyping was 100%, 83%, and 85%, respectively. Reproducibility of serotyping was 90% and of phage typing 96% if two major differences were allowed to differentiate between patterns. O-serotyping had the highest discriminatory power and combination of all typing methods further increased discrimination. Outbreaks of E. cloacae were not evident in clinical departments, but cross-infections from one department to another could not be completely ruled out. We concluded that the combination of bio-, phage- and O-serotyping is sufficiently discriminating and will be satisfactory in the majority of clinical situations.

Ribotyping of selected isolates of Enterobacter cloacae and clinical data related to biotype, phage type, O-serotype, and ribotype

In order to evaluate if ribotyping of selected isolates of Enterobacter cloacae could further elucidate the epidemiology, we performed ribotyping of 109 isolates indistinguishable by bio-, phage-, and O-serotyping, with inconclusive typing results, or from patients with more than one isolate. Ribotyping provided additional information, and some cases of cross-infection or common source of infection were revealed. Under the supposition that isolates sharing the same ribotype were of the same origin, problems arose with respect to bio-, O-sero, as well as phage typing; in particular a remarkable number of isolates showed differences in phage type. In order to identify possible virulence characteristics of certain types, clinical data were related to bio-, phage-, O-sero-, and ribotype. Biotype 66 was significantly more frequent among blood culture isolates (P = 0.001), but this might have reflected the presence of a certain strain in the environment of the intensive care unit, where patients were more likely to develop bacteraemia; serotype 04 was significantly more frequent among isolates from the urinary tract (P = 0.02), and serotype 013 was more frequent among women (P = 0.05). One ribotype was found only among community-acquired isolates, which might suggest that it is a frequent but less virulent strain.

Retrospective 6-year study of enterobacter bacteraemia in a Danish university hospital

In order to study the epidemiology of invasive enterobacter infections, data from 53 consecutive cases of bacteraemia due to this organism were compared with data from 72 randomly selected cases of Escherichia coli bacteraemia. The cases occurred among patients admitted to a Danish University hospital over a 6-year period. Forty-eight cases were due to Enterobacter cloacae and five were due to Ent. aerogenes. Enterobacter bacteraemia was more often of nosocomial origin than E. coli bacteraemia and more often polymicrobial. Patients suffering from enterobacter bacteraemia were younger than E. coli patients, and males tended to predominate. Apart from cancer of the prostate, other malignant diseases tended to be more frequent among patients with enterobacter bacteraemia than among E. coli patients. Enterobacter bacteraemia was more often associated with a focus in central venous catheters and burns, whereas patients with E. coli bacteraemia more often showed a focus of infection in the urinary tract. Patients with enterobacter bacteraemia and a microbiologically documented focus in the respiratory tract or the urinary tract more often had an endotracheal tube or indwelling urinary catheter compared to patients with E. coli bacteraemia with a similar focus of infection. In patients with no microbiologically documented focus enterobacter bacteraemia was more often associated with the presence of central and peripheral venous catheters. During the preceding 12 weeks patients with enterobacter bacteraemia, more often than E. coli patients, had been treated with beta-lactam antibiotics, especially penicillins. The close association with devices may indicate that Enterobacter has a special affinity for foreign body material. Studies are planned to elucidate this aspect in further detail.

The use of the PhP-KE biochemical fingerprinting system in epidemiological studies of faecal Enterobacter cloacae strains from infants in Swedish neonatal wards

The PhenePlate (PhP) biochemical fingerprinting system is an automated method for typing of bacteria, based on the evaluation of the kinetics of biochemical reactions, performed in microtitre plates. In the present study the PhP-Klebsiella/Enterobacter (KE) system was evaluated for typing of Enterobacter cloacae and employed to study the epidemiology of faecal E. cloacae strains isolated from infants in 22 Swedish neonatal wards. The PhP-KE system showed a high reproducibility and discrimination for E. cloacae isolates. Among 64 epidemiologically unrelated E. cloacae strains, 49 distinct phenotypes were found, and the diversity index was 0.985. E. cloacae was found as a part of the dominating Gram-negative aerobic bacterial flora in 83 out of 953 infants studied. The incidences of E. cloacae colonization varied between 0 and 35% in different wards, but in contrast to previous data for Klebsiella spp. and Escherichia coli, there was little evidence of spread of particular strains in the wards. We also discuss two different measures of nosocomial transmission of bacterial strains: transmissible strains and epidemic index.

Outbreak of cephalosporin resistant Enterobacter cloacae infection in a neonatal intensive care unit

Enterobacter cloacae resistant to third generation cephalosporins emerged rapidly during an outbreak of serious infections due to this organism in a neonatal intensive care unit where ampicillin and gentamicin were used as first line antibiotic treatment. Organisms resistant to cephalosporins were isolated from 12 infants, six of whom developed systemic infection. Two infants died. Isolates of E. cloacae from four of five infants treated with cefotaxime showed a loss of sensitivity to this antibiotic during treatment, but in the three infants who survived sensitive organisms were again isolated after treatment had stopped. Stopping treatment with the cephalosporins, closure of the unit to new admissions, and strict cohorting of colonised infants resulted in a prompt end to the outbreak. This outbreak suggests that the routine use of third generation cephalosporins for suspected sepsis may be inappropriate in the presence of a large reservoir of organisms with the potential for rapidly developing resistance. Routine bacteriological surveillance, however, might permit their use on a rotational basis.