Studies On The Clinical Characteristics, Drug Susceptibility And The Pattern Of An Out Break Of Acinetobacter Baumannii

The genus Acinetobacter is classified under the family Moraxellaceae and comprises strictly aerobic,Gram-negative,non-motile,non-lactose-fermenting, oxidasenegative,catalase-positive coccobacilli.More than 30 genomic species have been identified within this genus,17 of which have been assigned valid names. Acinetobacter baumannii(gen sp 2) is the species primarily associated with human disease.A baumannii can be found in various environmental sources such as soil,and foods,including vegetables,meat,and fish.A baumannii may rather infrequently colonise the skin of healthy human beings,typically at a low density and for short-term duration.Colonisation of other body sites such as the throat,nares,and the intestinal tract,has been found rarely in healthy individuals.A baumannii is emerging as a cause of numerous global out break,displaying ever-increasing rates of resistance.The rising incidence of multidrug-resistant A baumannii infections in health-care settings may in part be attributed to the ability of this organism to cause outbreaks.Acinetobacter spp are able to survive on dry inanimate surfaces for a prolonged time.Most studies have reported survival of about 1 month, although survival for up to 5 months has been noted.Furthermore,a baumannii has mechanisms that facilitate colonization of patients or of equipment used in medical care.Specific strains can attach to human epithelial cells through fimbriae or lipopolysaccharide side chains,bind to salivary mucins,and develop biofilm in contact with plastic or glass surfaces.The latter property may be of particular clinical relevance regarding catheter-associated infections.Last but not least,resistance to antimicrobial agents is one of the most important factors for the perpetuation of acinetobacter infections in health-care settings.The studies aimed to investigate the out break of Acinetobacter baumannii in our hospital by the methods of molecular epidemiology,to explore the antimicrobial resistance characteristics of pathogen and to determine the prevention strategies.1.Clinical characteristics of Acinetobacter baumanniiFrom April to June in 2007,most of the infection cases of Acinetobacter baumannii in our hospital were collected,Standard disk diffusion susceptibility tests were performed on the Acinetobacter baumannii which were isolated from the patient's body fluids including sputum,blood,urine,secretion,catheter and the ICU environment involving the patient's bed sheet,surface of patient's skin and medical staff's hands,humidification water of ventilator tubes.We found that Multi-drug resistance and Carbapenem resistant were the characteristics of the pathogen.The rate of resistance to Carbapenem was 75.4%(to meropenem was 85.5%and to Imipenem was 75.4%),Among the 19 tested agents,Colistin Sulphate and tigecycline showed high rates of antimicrobial activity against strains,The rate of susceptibility was 100%and 91.3%respectively. Moxifloxacin and minocycline had moderate antimicrobial activity against a baumannii,the rate of resistance being 63.8%and 36.2%respectively.Like the other agents,however,cefoperazone-sulbactam,piperacillin-tazobactam and Ticarcillin-clavulanic acid showed a low rate of antimicrobial activity,which the rate of resistance was 88.2%,76.8%and 82.6%respectively.2.The pattern of the outbreakA total of 62 strains of Acinetobacter baumannii belonging to 9 clones had been identified by PFGE(pulsed field gel electrophoresis).We found the clones A,B,and C were the dominant isolates and had spread widely among 12 departments in our hospital.Clone A was the dominant strain in the respiratory department,EICU and SICU,and all of the strains-A was made up by CRAb.Clones A and B were the dominant isolates in SICU.Clones A,B and C were popular isolates in EICU.The sub-clone A1 was isolated from the surface of unwashed medical staff's hands and patients' body fluids in the same period in SICU.That indicated a possible propagative method of Acinetobacter baumannii in a department.After investigating the cases we noticed that the pattern of the outbreak in our hospital was more likely caused by the transferred patients who were suffering from the infection or colonization by Acinetobacter baumannii.3.Clinical characteristicsThe study on the clinical characteristics of 55 cases showed the same risk factors which several studies have identified,including support with mechanical ventilation,(67%) particularly of prolonged duration,longer hospital or ICU stay(74 days in average),a higher number of interventions(85%),greater disease severity as measured by relevant scoring systems(APACHⅡwas 14±6 score),and administration of broad-spectrum antimicrobial agents,particularly third-generation cephalosporins(70%),β-lactamase inhibitors(73%).The mortality of MDRAb infection was 36%.The above results showed1.An outbreak of Acinetobacter baumannii in our hospital during April to June in 2007 was caused by MDRAb.The strains had spread widely among 12 departments especially in SICU,EICU and the respiratory department.2.Unwashed hands of medical staff after clinical procedures probably play a major role in the outbreak of MDRAb in the same department.And the pattern of the outbreak in our hospital was more likely caused by the transferred patients who were suffering from the infection or colonization by Acinetobacter baumannii.And EICU may be the origin of this outbreak.3.The study on the clinical characteristics of 55 eases showed the same results as several studies have identified.And those factors place a patient at increased risk for the acquisition of multidrug-resistant outbreak strains.