***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: A controlled r and omised prospect i ve study has been carried out on 100 male patients to compare the incidence of urethritis following catheterisation with either latex or silicone catheters .  All patients underwent elective cardiac surgery and were catheterised for 48 h with antibiotic cover , and were followed up for 6 months post-operatively . Of those with latex catheters 22 % developed urethritis , compared with 2 % of those in the silicone catheter group . This difference is statistically significant ( P less than 0.01 ) . Two of the former patients developed a decreased urinary flow and both had tight anterior urethral strictures The tendency to develop bacteriuria during the use of various forms of indwelling catheters was evaluated in a r and omized trial in 90 patients . A silver alloy and hydrogel-coated Foley catheter ( SHC ) was compared to a non-coated catheter ( NC ) and a catheter coated only with hydrogel ( HC ) . Three patients ( 10 % ) with SHC catheters , 10 ( 33 % ) patients with HC catheters , and 15 ( 50 % ) patients with NC catheters developed bacteriuria ( greater than 10(5 ) organisms/ml ) . The difference in the rate of bacteriuria after 5 days of catheterization was statistically significant between the SHC catheter and the NC catheter ( p less than 0.002 ) . There was no significant difference between the SHC catheter and the HC catheter , nor was there a significant difference between the HC catheter and the NC catheter . The toxic effects , as estimated by the IC50 value , of the urinary catheter material used was eluci date d in an experimental fibroblast model . The IC50 value for the NC catheter was 33.9 % , HC catheter 72.2 % and for the SHC catheter 98.1 % BACKGROUND Urinary tract infections ( UTIs ) account for 30 % to 40 % of nosocomial infections result ing in morbidity , mortality , and increased length of hospital stay . OBJECTIVE To assess the efficacy of a silver-alloy , hydrogel-coated latex urinary catheter for the prevention of nosocomial catheter-associated UTIs . METHODS A 12-month r and omized crossover trial compared rates of nosocomial catheter-associated UTI in patients with silver-coated and uncoated catheters .  A cost analysis was conducted . RESULTS There were 343 infections among 27,878 patients ( 1.23 infections per 100 patients ) during 114,368 patient-days ( 3.00 infections per 1000 patient-days ) . The relative risk of infection per 1000 patient-days was 0.79 ( 95 % confidence interval , 0.63 - 0.99 ; P = .04 ) for study wards r and omized to silver-coated catheters compared with those r and omized to uncoated catheters . Infections occurred in 291 of 11,032 catheters used on study units ( 2.64 infections per 100 catheters ) . The relative risk of infection per 100 silver-coated catheters used on study wards compared with uncoated catheters was 0.68 ( 95 % confidence interval , 0.54 - 0.86 ; P = .001 ) . Fourteen catheter-associated UTIs ( 4.1 % ) were complicated by secondary bloodstream infection . One death appeared related to the secondary infection . Estimated hospital cost savings with the use of the silver-coated catheters ranged from $ 14,456 to $ 573,293 . CONCLUSIONS The risk of infection declined by 21 % among study wards r and omized to silver-coated catheters and by 32 % among patients in whom silver-coated catheters were used on the wards . Use of the more expensive silver-coated catheter appeared to offer cost savings by preventing excess hospital costs from nosocomial UTI associated with catheter use . Arch Intern Med . 2000;160:3294 - 3298 The tendency of indwelling catheters to cause urinary tract infection was evaluated in a r and omised clinical study of 223 patients . A Foley catheter coated with silver alloy on both inner and outer surfaces was used in 60 patients ; 60 others received a Teflonised latex Foley 's catheter  and the remaining 103 patients were excluded because of antibiotic treatment , diabetes , etc . There was a statistically significant difference in the incidence of catheter-associated bacteriuria ( greater than 10(5 ) organisms/ml ) in the 2 groups after 6 days ' catheterisation : 6 patients with the silver coated catheter developed bacteriuria compared with 22 who had the Teflonised latex catheter . This suggests that the silver impregnated urethral catheters reduce the incidence of catheter-associated urinary tract infection OBJECTIVE To evaluate the efficacy of silicone-based , silver ion-impregnated urinary catheters in the prevention of  nosocomial urinary tract infections ( NUTIs ) . DESIGN Prospect i ve , crossover study to compare the efficacy of a silicone-based , hydrogel-coated , silver-impregnated Foley catheter with that of a silicone-based , hydrogel-coated catheter in the prevention of NUTIs . SETTING Adult medical and surgical wards of a university teaching hospital . RESULTS A total of 3,036 patients with catheters were evaluated ; 1,165 ( 38 % ) of the catheters were silver impregnated , and 1,871 ( 62 % ) were not silver impregnated . Study groups were not identical ; there were more men , a shorter duration of catheterization  , and fewer urine cultures per 1,000 catheter-days in the silver catheter group . The rate of NUTIs per 1,000 Foley-days was 14.29 in the silver catheter group , compared with 16.15 in the nonsilver catheter group ( incidence rate ratio , 0.88 ; 95 % confidence interval , 0.70 - 1.11 ; P = .29 ) . The median length of catheterization prior to the onset of a urinary tract infection ( ie , exposure time ) was 4 days for each group . There were no differences in the recovery of gram-positive , gram-negative , or fungal organisms in NUTIs . In a multivariate survival analysis , no factors , including silver catheters , were protective against NUTI . CONCLUSIONS Unlike previous trials of latex-based , silver ion-impregnated Foley catheters , we found that silicone-based , silver-impregnated Foley catheters were not effective in preventing NUTIs ; however , this study was affected by differences in the study groups . Prospect i ve trials remain important in assessing the efficacy and cost-effectiveness of new silver-coated products Catheters coated with hydrogel and silver salts have been proposed to prevent hospital-acquired urinary tract infections ( UTI )  . We carried out a r and omized , prospect i ve , double-blind multi-centre trial to compare those catheters with classical urinary tract catheters . We included in the study 199 patients requiring urethral catheterization for more than three days : 109 in group 1 ( classical catheter ) and 90 in group 2 ( catheter coated with hydrogel and silver salts ) .  Urine from the patients was tested for 10 days after the insertion of the catheter ( reactive dipsticks each day and diagnostic urinalysis every two days ) . The UTI associated with catheterization was defined on the basis of bacterial and cytological criteria ( > 10(5)cfu bacteria per mL and > 10 leucocytes per mm(3 ) ) . Twenty-two UTIs were recorded : 13 in group 1 and nine in group 2 . The cumulative incidence of UTI associated with catheterization was 11.1 % overall , 11.9 % for group 1 and 10 % for group 2 ; the odds ratio was 0.82 ( 95 % confidence interval : 0.30 to 2 . 20 ) ; the cumulative incidence for UTI , calculated by the Kaplan-Meier method was 36.3 overall , 35.2 in group 1 and 36.0 in group 2 ; the overall incidence density was 19 per thous and days of catheterization , 21 in group 1 and 18 in group 2 . The differences between the two groups were not significant . Overall , we feel that there is not enough evidence to conclude that catheters coated with silver salts and hydrogel give greater protection than classical catheters and to recommend widespread use Objectives : We performed two r and omized prospect i ve studies with the silver-coated Bardex IC catheter in order to evaluate the incidence of bacteriuria during short- and medium-term catheterization after urological procedures . Methods : During catheterization only consecutive suprapubic urine sample s were taken and cultured . After removal of the catheter the patient was allowed one wash-out void , and before the second micturition a suprapubic puncture was performed to collect a culture specimen . Results : In the first trial , after radical prostatectomy 18 patients with the Bardex IC catheter were compared to 17 patients with a silicon catheter  after the same procedure . There was no significant difference in bacteriuria after 14 days ( 50.0 vs. 53.3 % ) . In the second part of the study 180 patients were evaluated 101 with latex and 79 with Bardex IC catheters .  The median catheterization time was 5 days . The results show a significant delay in the onset of bacteriuria when a silver alloy catheter is used ( p < 0.003 ) . On day 5 only 6.3 % had bacteriuria in the Bardex IC group versus 11.9 % in the latex group . Conclusion : We conclude that , after urological procedures , short-term catheterization with the Bardex IC catheter is superior to the classical latex catheter 
    Output:
    
The authors state that previous studies demonstrated that silver alloy-coated catheters were more effective in reducing the incidence of urinary tract infection ( UTI ) than were uncoated latex-based catheters .
However , in their study , silver alloy-coated catheters were not more effective in preventing UTI than uncoated silicone catheters .
Perhaps silicone catheters simply have better properties than latex catheters and they are not incrementally improved by silver alloy coating .
Silicone catheters have been reported to have smoother surfaces than latex catheters .
Eluates from some of the latex products showed cytotoxicity and inhibited cell growth , whereas eluates from silicone catheters had less influence on cell growth .
Edwards et al. demonstrated that silicone catheters provoked fewer inflammatory reactions in rat bladders than did latex catheters .
A r and omized trial demonstrated that silicone catheters were associated with less penile discomfort and less purulent urethral discharge ( clinical urethritis ) than were latex catheters .
The lumens of silicone catheters are wider than those of latex-based catheters with similar external diameters .
Silicone catheters have been shown to be less prone to obstruction by encrustations .
Encrustations harbor large numbers of organisms , and encrustations on the external surface of the catheter may be a source of irritation and trauma .
Taken as a whole , current data suggest that commercially available silver-coated silicone urinary catheters only