nosocomial infections ( nis ) constitute an important health problem with high incidence , morbidity and mortality rates worlwide . nis have become particularly prominent in intensive care units ( icus ) , where the incidence is 2 to 5 times higher than in the general hospitalized population . intensive care unit patients are at greater risk of developing ni because of several reasons including presence of underlying diseases , longer stay , invasive diagnostic and monitoring procedures performed , impaired host defences , and colonization by resistant microorganisms . determination of risk factors for developing infection in icu patients is an important step for implementation of necessary precautions for prevention of infection . initial empirical antimicrobial treatment should be targetted against the most likely local pathogens , when a ni is suspected . therefore , the major concern of our study was the prospective assesment of the etiology and risk factors of nis in the icu of our hospital during a 1-year period . we conducted a 1-year prospective cohort study of nosocomial infection surveillance in a total 25-bed combined medical and surgical icu of the kartal teaching and research hospital , which is a 700-bed teaching hospital in istanbul , turkey . infection surveillance was implemented for all patients staying longer than 48 hours in the icu during the study period from january 1 , 2008 , to december 31 , 2008 . patients coming from icus of other hospitals or transferred to the icu from another clinic in the same hospital , or staying less than 48 hours in the icu were excluded . deep tracheal aspirate and urine samples were taken for culture on admission and repeated once a week . blood samples and/or removed intravascular catheter tips were cultured upon suspicion of bloodstream or catheter - related infection ( i.e. , fever , leucocytosis ) . any other samples ( from wounds , cerebrospinal fluid , etc . ) an infectious diseases specialist regularly visited the icu daily , followed all the patients there and collected data such as age , gender , cause of icu admission , underlying diseases , applied invasive procedures ( nasogastric tube , endotracheal intubation , mechanical ventilation , tracheotomy , urinary and intravenous catheterization , surgical operation ) , the acute physiology and chronic health evaluation ii ( apache ii ) score , length of stay , drug use , results of cultures , and administered antibiotics . by means of the cdc definitions of nosocomial infections , the decision of ni was made with a combination of both clinical evidence and laboratory findings . an appropriate antimicrobial therapy was administered to the patients based on local surveillance data and antibiotic susceptibility patterns of isolated microorganisms . the nosocomial infection rate was calculated as the number of all infections per 100 patients and per 1000 patient - days . isolated bacteria were identified by conventional methods and tested for antibiotic susceptibility by the kirby - bauer disc diffusion technique according to clinical and laboratory standards institute ( clsi ) specifications . for each case of icu - acquired nosocomial only the initial isolates were considered in the study and repeat isolates from the same sites were excluded . microbiologically documented bsi required 1 of the following : 1 ) recognized pathogen in the blood and pathogen not related to an infection at another site ; or 2 ) fever , chills , or hypotension and any of the following : a common skin contaminant isolated from at least 2 blood cultures drawn on separate occasions , and the organism is not related to infection at another site ; a common skin contaminant is isolated from blood culture in a patient with an intravascular device , and the physician institutes appropriate antimicrobial therapy . risk factors for nosocomial infection were recorded as age , sex , cause of admission to the icu , the acute physiology and chronic health evaluation ii ( apache ii ) score of patients on admission to the icu , any underlying diseases , surgical history , use of h2 receptor antagonists , central and/or peripheral intravenous access , nasogastric or endotracheal intubation , mechanical ventilation , urinary catheter , tracheostomy , and the length of stay in the icu . statistical analysis was done with spss ( statistical package for social sciences ) software , version 10.0 ( spss ) . chi - square test , mann - whitney u test and logistic regression analysis tests were used . statistical analysis was done with spss ( statistical package for social sciences ) software , version 10.0 ( spss ) . chi - square test , mann - whitney u test and logistic regression analysis tests were used . the data collected in this study belonged to 450 patients who stayed > 48 h in the icu with 6257 patient - days during one year . of the 450 patients , only 115 patients acquired nosocomial infections and the remaining 335 patients were non - infected . of the 450 patients , aged between 6 months and 91 years , 267 ( 59.3.% ) were male and 183 ( 40.7% ) were female . there were no significant differences in age and gender between patients with or without icu - acquired nosocomial infections . of the 450 patients , only 160 ( 35.5% ) patients had one or more underlying diseases . the most frequent underlying diseases were neoplasia , neurological disease and chronic obstructive pulmonary disease . no significant difference was observed when infected and non - infected cases were compared in terms of underlying diseases ( p=0.07 ) . the most frequent causes of admission to icu were respiratory failure ( 31.1% ) , trauma ( 24.7% ) and neurologic disease ( 22.9% ) ( table 1 ) . the apache - ii scores ranged between 5 and 40 , with a median of 20.465.6 , with no significant difference between infected and non - infected patients ( p=0.26 ) duration of stay in the icu was between 3 and 165 days , with a median of 15.4519.18 days in total study patients , 33.9227.02 days in the infected patients , and 8.126.08 days in the non - infected patients . . a total of 135 nosocomial infections were detected in 115 ( 25.6% ) of 450 patients . the incidence rate of nosocomial infections was 21.6 in 1000 patient - days , and the infection rate of nosocomial infections was 25.6% . the most frequent site of icu - acquired ni in our study was the bloodstream ( 49 , 36.3% ) , followed the respiratory system ( 41 , 30.4% ) , the urinary tract ( 25 , 18.5% ) , and catheter - related infection was diagnosed only in 10 patients , ( 7.4% ) . the distribution of isolated microorganisms by the sites of nosocomial infection is shown in table 2 . of all nosocomial infections , 112 ( 83% ) were microbiologically - confirmed ( culture - positive ) and 23 ( 17% ) were clinically - defined ( culture - negative ) infections . the pathogens of the culture - confirmed nosocomial infections were gram - negatives in 77 ( 68.8% ) , gram - positives in 31 ( 27.6% ) , and fungi in 4 ( 3.6% ) . among the 112 microorganisms , the most frequently isolated was pseudomonas aeruginosa ( 28 , 25% ) , followed by staphylococcus aureus ( 24 , 21.4% ) , escherichia coli ( 21 , 18.7% ) , acinetobacter baumannii ( 19 , 16.9% ) , and klebsiella spp . when the infected and non - infected patients were compared according to risk factors with univariate analysis , there was no significant difference with respect to age , gender , apache ii scores , surgical history , presence of urinary and/or nasogastric catheters , or use of h2 receptor antagonists ( p>0.05 ) . length of icu stay , central venous catheterization , mechanical ventilation and tracheostomy were identified as statistically significant risk factors for developing nosocomial infection ( p<0.05 ) . extrinsic risk factors in infected and non - infected patients are shown in table 3 . assesment of infections acquired in icus , determination of their risk factors and establishment of correct treatment protocols are crucial steps in prevention and management of infections in icus . we planned this prospective surveillance study to determine the incidence , etiology and risk factors for ni in icu patients at the kartal teaching and research hospital , istanbul , turkey . . there may be variations in the incidence of icu infections between centres , depending on the characteristics of patients and icus . in a point - prevalence study including 1417 centres in 17 european countries , the infection rate in icus was reported to be 20.6% . the infection rates in icus in several other studies reported by authors namely were as follows : legras et al . : 21.6% , appelgren et al . : 34% , aly et al . : 10.6% , ylipatosani et al . : 23.9% , and urli et al . : when we reviewed the rates of nosocomial infections reported in icus in our country , they differed from centre to centre . ( who reviewed the data of 56 icus in a 1-day point - prevelance study ) as 48.7% , and erbay et al . as 26% [ 1113 ] . the hospital infection rate per 100 patient admissions in our hospital was calculated as 25.6% . several studies have determined the risk factors for icu - acquired infections . although some studies reported the patient age over 70 and the presence of underlying diseases to be a risk factor , the age and underlying diseases of the patients were not statistically significant risk factors for icu - acquired infections in our study . a positive correlation between rates of nosocomial infections and average length of icu stay have been reported in various studies [ 12,1417 ] . in accordance with the results of these studies , length of icu stay was a significant risk factor for icu - acquired infection both in univariate and multivariate analyses in our study . there was a direct correlation between central venous catheterization , tracheostomy , mechanical ventilation and the risk of infection in our study , in agreement with the results of other studies . the most commonly reported sites of nosocomial infections in icus are the respiratory tract , followed by the urinary tract and the bloodstream , but the distribution of the sites and causes of infection may differ between centres . table 4 shows the distribution of common nis reported from icu studies in various centres . in general , the most common type of infection in icu is pneumonia , although markogiannakis et al . reported bacteremia as the most commonly encountered icu infection followed by pneumonia similar to the results in our study [ 8,1113,16,17,1921 ] . the higher occurrence of bsi seems to be closely related to specific and well - known risk factors such as the presence of indwelling venous catheters , and one or more critical underlying condition . in majority of studies , gram - negative bacteria have been reported as the most common cause of icu - acquired infections , but there were differences in rates of their distribution at the species level between centres . enterobacteriaceae ( 25.9% ) , p. aeruginosa ( 17.2% ) , s. aureus ( 10.9% ) and coagulase - negative staphylococcus ( cns ) ( 4.1% ) were the most frequent microorganisms reported by leon rosales et al . similarly , vincent et al . reported that the most frequent micro - organisms were enterobacteriaceae ( 34.4% ) , s. aureus ( 30.1% ) , p. aeruginosa ( 28.7% ) , cns ( 19.1% ) and fungi ( 17.1% ) ( 5,15 ) . in the study of tennant et al . , p. aeruginosa ( 41.3% ) was the most common organism , followed by acinetobacter spp ( 33.5% ) , cns ( 20% ) and streptococcus group d ( 18.7% ) ( 18 ) . similarly , various studies on icu infections performed in our country reported that gram - negative bacteria were the most frequent pathogens causing icu infections . data on distribution of micro - organisms frequently isolated by erbay et al . in icus of various turkish hospitals were as follows : p. aeruginosa ( 22.6% ) , methicillin - resistant s. aureus ( 22.2% ) and acinetobacter spp . reported p. aeruginosa ( 20.8% ) , acinetobacter spp ( 18.2% ) , s.aureus ( 18.2% ) and klebsiella spp ( 16.1% ) as the common pathogens . whereas , s. aureus ( 30.9% ) , acinetobacter spp ( 26.8% ) , p. aeruginosa ( 12.4% ) were the most freguent etiologic agents reported by meri et al . the most common cause of icu infections was p. aeruginosa ( 25% ) , followed by s. aureus ( 21.4% ) , e. coli ( 18.7% ) , and a. baumannii ( 16.9% ) , in decreasing order . the major pathogen causing bloodstream infections was s. aureus , whereas in case of pneumonia and urinary tract infection , p.aeruginosa and e.coli , were the most common bacteria , respectively . in conclusion , the bloodstream was the most common site of infection in our icu . central venous catheterization , mechanical ventilation , tracheostomy and longer stay in icu were common risk factors for icu - acquired infections . etiologic agents , site and rate of icu - acquired infections differ from centre to centre . therefore , each hospital should define their own risk factors for infection , regularly conduct surveillence study of the infectious etiologies of ni , and establish prevention and treatment strategies accordingly , in order to improve the quality of health care .
summarybackgroundto evaluate the incidence , risk factors and etiology of nosocomial infections ( nis ) in the intensive care unit ( icu ) of our hospital in order to improve our infection control policies.material/methodsa 1-year prospective cohort study of nosocomial infection ( ni ) surveillance was conducted in our icu in 2008.resultsout of 1134 patients hospitalized in the icu for a period of 6257 days , 115 patients acquired a total of 135 nis distributed as follows : 36.3% bacteremia , 30.4% ventilator - associated pneumonia ( vap ) , 18.5% catheter - associated urinary tract infection , 7.4% central - line infection , 5.9% cutaneous infection , and 1.3% meningitis . 
 the incidence rate of ni was 21.6 in 1000 patient - days , and the rate of ni was 25.6% . 
 length of icu stay , central venous catheterisation , mechanical ventilation and tracheostomy were statistically significant risk factors for ni . 
 of all ni , 112 ( 83% ) were microbiologically - confirmed and 68.8% of the isolates were gram - negative , 27.6% were gram - positive , and 3.6% were fungi . 
 23 ( 17% ) were clinically - defined infections . 
 the most frequently isolated organism was p. aeruginosa ( 25% ) , followed by s. aureus ( 21.4% ) , e. coli ( 18.7% ) and a. baumannii ( 16.9%).conclusionsthe bloodstream was the most common site and gram - negatives were the most commonly reported causes of icu infections .