Study On Risk Factors And Molecular Typing Of Nosocomial Acinetobacter Baummanii Pneumonia

PartⅠRisk factors for acquisition of hospital-acquired pneumonia of carbapenem-resistant Acinetobacter baumannii in intensive care unitObjective To study the bacteriological and epidemiological characteristics of nosocomial Acinetobacter baummanii infections and to identify the risk factors associated with acquisition of hospital-acquired pneumonia of carbapenem-resistant Acinetobacter baumannii(CRAB) in intensive care unit(ICV).Methods A retrospective case control study of all patients who had nosocomial A.baumannii pneumonia in ICU between July 1,2006 and June 30, 2008.Only the first isolation of A.baumannii was considered.Antibiotic susceptibilities of the isolates were determined by the standardized disk-diffusion method according to the recommendations of CLSI(formerly the National Committee for Clinical Laboratory Standards). All statistical analyses were performed using SPSS v.16.0.The a value was set at P＜0.05.Results CRAB was isolated from 40 patients but 10 are excluded,30 patients associated with hospital-acquired pneumonia of carbapenem-sensitive Acinetobacter baummanii(CSAB) were selected and compared with controls during the study period.The mean duration of hospital stay until A.baumannii isolation was 23.37±21.70 days in CRAB infections,whereas it was 13.23±8.41 days in CSAB infections.Previous carbapenem use was present in 46.7% of the patients with CRAB and 16.7%of the patients with CSAB infection.The average mechanical ventilation time was 12.53±11.38 days in CRAB and 5.67±3.72 days in CSAB(P=0.013).Most of the isolates were multidrug resistant.Resistance of CRAB to ceftazidime,cefepime,ceftriaxon,amikacin,ciprofloxacin,piperacillin, gentamicin and piperacillin-tazobactam was higher than 45%,while resistance to ampicillin-sulbactam and cefoperazone-sulbactam was low.In univariate analysis APACHE(Acute Physiology And Chronic Health Evaluation)Ⅱscore 20 at admission in ICU,longer duration of hospital stay until infection, mechanical ventilation time,previous administration of carbapenems,number of antibiotic classes received,longer time of antibiotic use and mixed use of antibiotic were significant risk factors for CRAB infections(P＜0.05), but there was no difference in ICU stay days between the two groups.In multivariate analysis,previous administration of carbapenems(odds ratio(OR) 6.229,longer time of antibiotic use until A.baumannii isolation(OR 1.067), previous hormone use(OR 1.170),and APACHEⅡscore≥20(OR 4.572) were independently associated with CRAB acquisition.Conclusions Our results suggest that the nosocomial occurrence of CRAB is strongly related to previous administration of carbapenems,longer time of antibiotic use until A.baumannii isolation,longer mechanical ventilation time and state of an illness(APACHEⅡscore≥20) and that CRAB occurrence may be favored by the selection pressure of previously used antibiotics.PartⅡThe Homogeneity of Carbapenem- resistant Acinetobacter BaumanniiObjective To investigate the homogeneity and molecular epidemiology of carbapenem- resistant Acinetobacter baumannii(CRAB) isolates selected from different wards of the Zhongshan Hospital,and to offer evidence for establishing the measure to prevent and control hospital onset of infection.Methods The identification and antimicrobial susceptibility test of Acinetobacter baumannii were done according to the standardized protocol.The pulse - field gel electrophoresis(PFGE) was used to type the resistance isolates gathered in our hospital,determining whether they derived from the same clone or not.Result 63 strains of CRAB were recovered from patients admission between 2007 and 2008 in our hospital,25 from the S-ICU,10 from the E-ICU,12 from the respiratory ward and 16 from emergency observation room.A total of 11 distinct genotypic patterns were identified using PFGE(A,C-M) and each had formed one to seven subtypes.In the last two years,PFGE types C and E were the dominate clone including 20 and 20 clonally related strains,respectively. We found possibly clonally relationship among the type A,E(44.4%)and H as well as type C and G(38.1%).Although no specific clone was spread among several wards during the entire study period but rather one clone dominated in each ward respectively.For example,clone C dominated in SICU,while clone G1 in EICU,clone E in respiratory ward and emergency observation room.During February to June in 2005,2 different PFGE genotypes were detected in 5 strains of CRAB(A and B) from SICU,of which clone B accounted for 80%.None of the clone B appeared in 2007 and 2008.PFGE type A was first isolated from a patient in the respiratory ward in February 2005,and other strains in this clone were isolated from the respiratory wards and other wards of the hospital during the following years(until December 2008).Conclusion To our knowledge,this is the first Homogeneity description of CRAB infection in our hospital.PFGE types C and E were the dominate clone in our hospital in the last two years and clone G1 and clone E would cause the spread of CRAB infection.There' s one respective clone dominated in each ward,which suggested that the increasing rate of CRAB infections is corresponded to the spread of the close clonally related strains.In contrast to carbapenem-resistant strains collected in 2005,PFGE types have changed in 2007 and 2008.Clonally related strains can survive for a long time in our hospital and cause nosocomial infections at various times in different wards. The spread of CRAB was mostly due to the contamination of environment.