Eur J Clin Microbiol Infect Dis (1998) 17:73-77 Springer-Verlag 1998 Editorial Acinetobacter Species as Nosocomial Pathogens D. H. Forster, F. D. Daschner Acinetobacter is a gram-negative coccobacillus that is of the isolates were identified as A. baumannii [4]. Of strictly aerobic, nonmotile, catalase positive, and oxi- these A. baumannii strains, 48.8% were isolated from dase negative. It is widespread in nature, being found in respiratory tract specimens, 26.5% from blood cultures soil and water. Acinetobacter, like other nonfermenta- and from central venous lines, 16.4% from wound rive gram-negative bacteria, has been recognized as a swabs, and 8.3% from other sites. The remaining 27.1% nosocomial pathogen since the 1970s. The introduction of the strains isolated belonged to other species, of of new broad-spectrum antibiotics in hospitals has been which the most frequent were Acinetobacter genomic one of the main factors responsible for this develop- species 3 (9.4%), A. johnsonii (5.0%) and A. Iwoffi ment. (3.6%). The key features of nosocomial infections with Acineto- In general, identification rates of A. baumannii must be bacter spp. have been described as the propensity of interpreted cautiously, especially those in older reports, Acinetobacter to affect severely ill patients, especially because phenotypic identification methods for Acineto- "those on artificial ventilation, the limited therapeutic bacter spp. are not totally reliable. Identification of the options due to multiple-antibiotic resistance, and the clinically important species 2 (A. baumannii), 3, and 13 contamination of the patients' environment, creating a TU is particularly difficult [3]. potential reservoir for patient-to-patient transmission [1]. Nosocomial Infections due to Acinetobacter Species Taxonomy of Acinetobacter and Clinically Important Species The most common site of nosocomial infections is the respiratory tract, especially in ventilated patients, fol- The taxonomy of Acinetobacter spp. has changed fre- lowed by the bloodstream. Less frequently, the urinary quently. Up to now 21 genomic species have been de- tract, surgical wounds, the central nervous system, the scribed [2]. Some of the species have formal names: A. peritoneum, the skin, and the eye are involved. baumannii, A. johnsonii, A. calcoaceticus, A. haemolyti- cus, A. junii, A. Iwoffii, and A. radioresistens. There is a According to data from the National Nosocomial Infec- close relationship between the genomic species 1 (A. tions Surveillance (NNIS) system from 1990-1992, Aci- calcoaceticus), 2 (A. baumannii), 3, and 13 TU, which netobacter spp. were isolated in 1% of all nosocomial are sometimes named as the A. calcoaceticus-A.bau- infections [5]. The true frequency of nosocomial infec- mannii complex, corresponding quite well to the species tion caused by Acinetobacter spp. is difficult to assess previously named as A. calcoaceticus var. anitratus [3]. because isolation of Acinetobacter spp. in clinical speci- mens may reflect colonization rather than infection. For typing methods the reader is referred to the Acine- tobacter review of Bergogne-B6rdzin and Towner [3] Acinetobacter spp. were isolated in 4% of all cases of and the study of Ehrenstein et al. [2]. Clinically, the nosocomial pneumonia in NNIS hospitals [5]. In me- most important species is A. baumannii. In one study chanically ventilated patients, however, Acinetobacter that included 584 clinical Acinerobacter isolates, 72.9% occurs more frequently. Acinetobacter, like Pseudo- monas aeruginosa and Stenotrophomonas maltophilia, is a typical pathogen in late-onset ventilator-associated pneumonia [6]. According to studies in which diagnosis D. H. Forster, F. D. Daschner (EN) Institute for Environmental Medicine and was supported by analysis of protected brush speci- Hospital Epidemiology, University Hospital Freiburg, mens, Acinetobacter spp. are involved in 4-26% of ven- Hugstetter Strasse 55, D-79106 Freiburg, Germany tilator-associated pneumonia cases [6-11]. Acinetobac- 74 ter is thus one of the leading pathogens that cause ven- was found to be lower than that in the general popula- tilator-associated pneumonia, the prognosis of which tion. In two of these studies, the majority of bacteremic may be as poor as that of ventilator-associated pneu- episodes were catheter-related [14, 19]. In catheter-re- monia caused by Pseudomonas spp. In one study by Fa- lated bloodstream infections due to Aci~wtobacter john- gon et al. [12], mortality associated with Acinetobacter sonii, a similarly good outcome has been described or Pseudomonas pneumonia in ventilated patients was [20]. 71%, with an attributable mortality of 43%. A. bau- mannii is also one of the main causative agents of sinu- Secondary meningitis is the most frequent type of Aci- sitis in mechanically ventilated patients [13], a condi- nelobacter meningitis, the mortality rate being around tion that is associated with an increased risk of pneu- 25%. Risk factors inclade the presence of ventriculos- monia in these patients. tomies, cerebrospinal fluid fistulas, indwelling ventricn- lar catheters (especially if present more than 5 days), According to NNIS data, Acinetobacter spp. are found and overuse of antimicrobial agents in neurosurgical in 2% of all nosocomial bloodstream infections [5]. Aci- ICUs [3, 21]. netobacter baumannii bacteremia is usually acquired in the intensive care unit (ICU). Mortality rates in pa- Acinetobacter spp. are isolated in 1% of the cases of tients with Acinetobacter baumannii bacteremia range nosocomial urinary tract infections and surgical site in- from 17%-52% [14, 15]. In two larger recent studies, fections [5]. Moreover, Acinetobacter can be a cause of the mortality rate among patients with A. baumannii peritonitis in patients undergoing continuous ambulato- bacterelnia was 44% and 52%, respectively [14, 15]. In ry peritoneal dialysis and of choloangitis and sepsis fol- the study of Cisneros et al. [t5], death was related to lowing percutaneous transhepatic chotangiography or the bacteremia in 65% of the patients who died. biliary drainage [22~. Other infections, such as ophthab mic infections and osteomyelitis, seem to be very rare Septic shock is a common complication in these pa- [3]. Severe underlying diseases, extended ICU stay, tients, occurring in 25-30% of patients. In the two stud- prolonged respiratory therapy, and previous antibiotic ies mentioned above [14, 15], polymicrobial bacteremia therapy have been identified as predisposing risk fac= was observed in 35% and 19% of patients, respectively. tots for the acquisition of resistant Acinetobacter spp. in Multivariate logistic regression analysis in the study of the ICU [23, 24]. Seifert et al. [14] revealed the following independent predictors of mortality: rapidly or ultimately fatal dis- ease, septic shock, and mechanical ventilation. Cisneros Epidemiology of Acinetobacter Species et al. [15] identified disseminated intravascular coagula- tion and inappropriate antimicrobial treatment as inde- In 1979 the Centers for Disease Control described a pendent risk factors for mortMity in patients with Aci- seasonal pattern of Acinetobacter infections with an in- netobacter bacteremia. fection rate that was twice as high in late summer as in the early winter for each year in the study period from The major portals of entry of Acinetobacter into the 1974 to 1977 [25]. This pattern was seen in all services bloodstream are the respiratory tract and vascular de- and all major infection sites for A. calcoaceticus vat. an- vices. Other less frequently involved portals of entry itratus. Temperature and humidity changes were dis- are the urinary tract, the abdomen, the skin and soft cussed as the possible reasons for this finding [3, 21, tissue, the central nervous system, and burn wounds 26]. [14]. Multiple sources of bacteremia are possible, but the source frequently cannot be determined. Intestinal Acinetobacter spp. are present on the skin of at least translocation as a possible source in these cases has one-fourth of healthy male individuals [27], particularly been discussed [15J. in moist regions such as the a• the groin, and toe webs [3]. Oropharyngeal or rectal carriage is rare. In a Patients with A. baumannii bacteremia associated with recent study that included more than 300 patients ad- intravascular catheters seem to have a good prognosis, mitted to a surgical ICU, less than 4% of the patients probably because the source of infection can be elimi- were colonized with A. baumannii on admission to the nated by removing the catheter. The mortality among unit when screening cultures of stool samples, nasal and 72 patients with epidemic Acinetobacter baumannii bac- pharyngeal swabs, tracheal secretions, and urine were teremia associated with contaminated pressure trans- performed [28]. Acinetobacter spp. were found on the ducers used for arterial catheters was not significantly hands of 19% of hospital personnel and may be re- higher than that among controls [16]. In the study of garded as a part of the nontransient flora [29]. Non- Seifert et al. [14], catheter-related infection was also as- transient Acinetobacter and other gram-negative bacilli sociated with an increased chance of survival, whereas on the hands of hospital personnel are thus a potential all eight patients with pneumonia as the primary site of reservoir of hospital strains. Patient contact has not infection died. Moreover, mortality in preterm neon- been found to be an obvious source for the acquisitien