Acinetobacter Baumanii As Lower Respiratory Tract Infection: Epidemiology, Drug Resistance And Correlation Factor

Background and ObjectivesFor the past few years,to control the nosocomial infection caused by multidrug resistant gram-negative bacteria is constantly the important problem in the field of medicine.Although many new antibiotics had come out and been used extensively, effectivelly decreased the rate of nosocomial infections caused by Enterobacteriaceae,they increased the number of Nonfermentative bacteria such as Pseudomonas aeruginosa,Acinetobacter baumannii.In the past,the infections caused by A.baumannii were rare,now because of extensive use of broad-spectrum antibiotics,the isolation rate of A.baumannii is increasing year by year and the second highest,just lower than that P.aeruginosa.A.baumannii has emerged as an important nosocomial pathogen that is mainly responsible for lower respiratory tract infections,also comprising bacteremia,meningitis,soft tissue infection,peritonitis and so on.A.baumannii was usually highly resistant to antibiotics,exhibited multidrug-resistance,especially resistant to carbapenem which was very difficult to treat,so A.baumannii has been nicknamed the "Gram-negative MRSA".Furthermore, A.baumannii resistant to soap can survive for a longer time in hospital environment, and was the most common gram-negative bacteria isolated from the hand of medical workers.In this way,A.baumannii can increase the hazard of cross infection between the patients,easily result in nosocomial outbreak.We should enhance the study of A.baumannii,so as to provide effective scientific basis for its prevention and treatment.Although the study of A.baumannii were considerably reported in the world, because of the difference among environment,sterilized measure,therapeutic tool and risk factors in different regions,so there were significant differences in antimicrobial resistance.For this reason,we should master the epidemiological characteristics and drug resistance in our own hospitals,which is of practical importance to prevent and control nosocomial infection.Therefore,this study had analyzed the data of 198 cases of lower respiratory nosocomial infection caused by A.baumannii,which was discussed as follows:(1)To investigate epidemiological characteristics and drug resistance retrospectively,(2) To study the risk factors and prognosis of hospital acquired pneumonia caused by carbapenem-resistant A.baumannii,(3) To analyze the factors influencing bacterial clearance and treatment strategy.MethodsWe analyzed the clinical data of 198 case of lower respiratory tract infections caused by A.baumannii from January,2005 to December,2007.Meanwhile,a total of 356 A.baumannii isolates were collected to study.1,By descriptive epidemiological methods,the reported epidemic data was analyzed retrospectively.2,Susceptibility of 356 strains of A.baumannii to 14 kinds of antimicrobial agents was detected by standard K-B methods.3,By a case-control study,the risk factors and prognosis of 44 cases of nosocomial infection caused by CRAB were analyzed.4,According to the bacteria therapeutic effect criteria,the patients were categorized as clearance group(n=86) and non-clearance group(n=112).Bacterial eradication rate and the factors influencing bacterial clearance were analyzed respectively.5,All statistical tests were operated with the program SPSS13.0,statistical data was expressed by(?)±SD,Univariatesis(T test and chi-square test) and multivariate logistic regression were used for statistics analysis.All tests were two-tailed,and a value of P≤0.05 was considered significant.Results1,Most of A.baumannii were from lower respiratory tract(79.2%,595/751).The isolation rate of A.baumannii tended to increase year by year(2005:9%, 2006:13.2%,2007:16.3%).The rate of infection was 59.8%(356/595).A. baumannii strains were mainly distributed in the ICUs(70.8%,252/356),ICU of neurology department as the most ones.Most of these patients were diagnosed as stroke in hospitalization.Their mean age was 49.4 years,the ratio of male to female was 2.0:1.There were A.baumannii cases reported in the whole years.Our data of continuous 3 years showed that the rate of monthly infection had 3 epidemic peaks in April,July,September,with the difference less than one month.2,The antibiotic susceptibility test in vitro showed:Drug resistance of A.baumannii was a serious problem,77.2%(275/356)of stains showed multiple resistance. Imipenem(76.7%susceptible) and meropenem(74.2%susceptible) were the most active agents against A.baumannii,followed by cefoperazone-sulbactam(67.1% susceptible),the intermediate rate to cefoperazone-sulbactam(28.1%intermediate) was highest,and other 11 kinds of antimicrobial agents were less than 30%.The resistant rate to cefoperazone-sulbactam was lowest.The resistance rates to cefoperazone-sulbactam,imipenem and meropenem were less than 50%in ICU. Except cefoperazone-sulbactam,the resistance rate in the ICU was(11.1%～31.2%)higher than the others with significant difference(P＜0.05).Less than 11% of carbapenem resistant strains were resistant to cefoperazone-sulbactam,others were over 80%.3,Positive correlation(r=0.896,P=0.000) and linear regression(R~2=0.803)existed between imipenem and meropenem in diameter of inhibition zone,and the regression equation was Y=0.928X+1.241.4,Univariate analysis revealed that five factors associated with the infection caused by CRAB were APACHEⅡscore,chronic pulmonary disease(COPD/bronchiectasis), imipenem/meropenem and fluoroquinolone used 15 days before isolation of CRAB, and early combination therapy of antibiotics.Multivariate logistic regression analysis identified two independent factors:APACHEⅡscore(OR=1.40,95% CI=1.19～1.64) and imipenem/meropenem used 15 days before isolation of CRAB (OR=5.57,95%CI=1.71～18.18).5,Of 44 cases of CRAB infections,14 patients died and 30 patients survived. Univariate analysis revealed that two factors associated with poor prognosis were organ failure,clinical pulmonary infection score(CPIS) rise after three-day treatment. According to multivariate logistic regression analysis,only CPIS rise after three-day treatment(OR=7.01,95%CI 1.23-40.03) was an independent predictive factor.6,The total bacterial eradication rate of lower respiratory infection caused by A.baumannii was 43.4%,but in MDR and Non-MDR A.baumannii was 36.0%, 59.7%respectively(x~2=9.693,P=0.002).The factors influencing bacterial clearance were APACHEⅡscore,MDR,coma,mechanical ventilation,tracheal intubation/incision and CPIS rise after three-day treatment(P＜0.05).7,In clearance group,57 cases were treated according to the results of susceptibility testing and recommended antibiotics,average duration of bacterial clearance was (17.6±9.7) d.Oppositely,29 cases were not treated according to this criteria, average duration of bacterial clearance was(23.8±17.1) d.The factors significantly influencing duration of bacterial clearance were MDR,APACHEⅡscore≥15, mechanical ventilation and tracheal intubation/incision(P＜0.01).8,Different therapeutic strategies(Antimicrobial monotherapy or combination therapy) influencing duration of bacterial clearance were compared,the results showed that In Non-MDR A.baumannii group(n=37),monotherapy vs combination therapy, Z=-0.198,P=0.843;In MDR A.baumannii group(n=20),monotherapy vs combination therapy,Z=-1.941,P=0.052. Conclusion1,The main side of A.baumannii infection is lower respiratory,strains represented severe multiple-resistance.It is important to monitor closely the key departments, vulnerable population and high occurrence time,take effective measures promptly, so as to prevent and control nosocomial infection.2,Carbapenems are still the most active agent against A.baumannii,but the resistant rate to cefoperazone-sulbactam was lowest,and the intermediate rate was highest.So it is possible to improve therapeutic effect by adding doses within safety margin,especially for CRAB.3,Imipenem showed the same sensitivity as meropenem.So it seems to be impossible to alternate medicine between these two drugs.4,APACHEⅡscore and imipenem/meropenem used 15 days before isolation of CRAB were independent risk factors for CRAB infection.CPIS rise after three-day treatment was a predictive factor for the prognosis of CRAB infection.5,The main factors influencing bacterial clearance were APACHEⅡscore,MDR, coma,mechanical ventilation,tracheal intubation/incision and CPIS rise after three day treatment.6,In order to attain satisfactory effect on bacterial clearance,duration of therapy is at least two weeks.It needs prolonged therapy for the patients who have risk factors.It is not significant on duration of bacterial clearance between monotherapy or combination therapy.