the 42 participating spanish hospitals were selected according to earss criteria ( 1,7 ) . the total catchment population was 9 million people , or 22.5% of the spanish population . the first blood e. coli isolates obtained from each patient between 2003 and 2006 were included . each laboratory identified the strains and tested their susceptibilities according to standard microbiologic procedures ; all used commercial microdilution systems . susceptibility data were interpreted according to clinical laboratory standards institute criteria ( 8) . for epidemiologic purposes , intermediate susceptibility to amc was considered as resistance . multidrug resistance was defined as resistance to > 3 of the following antimicrobial agents : ciprofloxacin , gentamicin , cotrimoxazole , and cefotaxime . to assess the comparability of susceptibility test results , an external quality assurance exercise ( uk national external quality assessment scheme ) was performed yearly . hospital - acquired infections were defined as infections acquired at least 48 hours after hospital admission . outpatient consumption of penicillin/-lactamase inhibitors ( world health organization code j01cr02 ) for the period 20022006 was assessed from the especialidades consumo de medicamentos database , which showed retail pharmacy sales of all medicines acquired with national health system prescriptions and covered nearly 100% of the spanish population ( 5 ) . the information was tabulated , and the number of units was converted into defined daily doses ( ddd ) of active drug ingredients according to who methodology ( 9 ) . the number of ddd per 1,000 inhabitants per day ( dids ) was calculated for each active drug ingredient . differences in the antimicrobial resistance prevalence between different groups were assessed by fisher exact test . association was determined by calculation of the odds ratio ( or ) with 95% confidence intervals ( ci ) . statistical analyses were performed by using graphpad prism version 3.02 software ( graphpad software , inc . participating hospitals reported data on 9,090 cases of e. coli bacteremia during the study period , corresponding to the same number of patients ; 4,526 ( 49.8% ) were male patients and 4,564 ( 50.2% ) were female patients . a total of 1,531 cases ( 16.8% ) were diagnosed in 2003 ; 2,526 ( 27.8% ) in 2004 ; 2,438 ( 26.8% ) in 2005 ; and 2,597 ( 28.6% ) in 2006 . of the total number of isolates , 328 ( 3.6% ) were obtained from children < 14 years of age ; 2,857 ( 31.4% ) were obtained from patients > 15 and < 64 years of age ; and 5,909 ( 65% ) were obtained from patients > 64 years of age . there were 3,384 ( 37.9% ) isolates implicated in hospital - acquired infections and 5,540 ( 62.1% ) in community - acquired infections ; information was missing for 166 cases . of the 9,090 e. coli isolates tested , 1,136 ( 12.5% ) were nonsusceptible to amc , 5.1% were resistant , and 7.4% were intermediate . the prevalence of amoxicillin / clavulanic acid nonsusceptibility in relation to gender , age , infection origin , and resistance to other antibimicrobial drugs is detailed in the table . * the most prevalent phenotypes included multidrug resistance to ciprofloxacin , cotrimoxazole , and gentamicin , which was detected in 73 nonsusceptible amc isolates ( 36.9% of multiresistant isolates and 6.4% of isolates overall ) , and resistance to ciprofloxacin , cotrimoxazole , and cefotaxime was detected in 55 isolates ( 27.8% of multiresistant isolates ; 4.9% of isolates overall ) . multidrug resistance was more prevalent in nosocomial ( 23.5% ) than in community - acquired isolates ( 15.1% ; or 1.99 , 95% ci 1.462.72 ; p<0.0001 ) . among nonsusceptible amc isolates , susceptibility to other antimicrobial drugs , including ciprofloxacin , gentamicin , cefotaxime , and cotrimoxazole , was more frequent in community- ( 28.7% ) than in hospital - acquired isolates ( 13.3% ; or 1.68 , 95% ci 1.272.22 ; p = 0.0003 ) . the overall rate of invasive e. coli nonsusceptibility to amc increased from 9.3% ( 2003 ) to 15.4% ( 2006 ) (  test for trend 36.51 ; p<0.0001 ) ( figure 1 ) ; this increase was observed in 64.3% of the participant hospitals . this increase was also detected in both intermediate and resistant isolates , with annual distributions of 5.6% and 3.8% , respectively , in 2003 ; 6.8% and 4.8% in 2004 ; 7.5% and 5.4% in 2005 ; and 9.4% and 6% in 2006 . evolution of amoxicillin - clavulanic acid nonsusceptibility of escherichia coli from blood isolates , spain , 20032006 . amc nonsusceptibility according to age groups increased over the study period as follows : children < 14 years of age ( 10.6% in 2003 , 14.6% in 2004 , 14.3% in 2005 , and 16.3% in 2006 ) ; patients > 15 and < 64 years 9.6% in 2003 , 11.2% in 2004 , 11.7% in 2005 , and 13.3% in 2006 ) ; patients > 64 years ( 8.8% in 2002 , 11.3% in 2004 , 15.9% in 2005 , and 16.3% in 2006 ) . the prevalence of amc nonsusceptibility in community - acquired infections increased from 8.9% ( 2003 ) to 15.6% ( 2006 ) (  test for trend 29.43 ; p<0.0001 ) . amc nonsusceptibility in nosocomial infections increased from 9.2% ( 2003 ) to 15.2% ( 2006 ) (  test for trend 11.94 ; p = 0.0006 ) . in the final 2 years of the study period ( 20052006 ) this increase was due to community - acquired e. coli isolates only ; the nonsusceptible proportion varied from 11.5% ( 2005 ) to 15.6% ( 2006 ) ( or 1.42 , 95% ci 1.161.74 ; p = 0.0009 ) in community - acquired isolates compared with 15.4% ( 2005 ) to 15.2% ( 2006 ) in hospital - acquired isolates ( figure 1 ) . community - acquired infection probably included healthcare - associated infections , a recently described epidemiologic category distinct from both community - acquired and nosocomial status . in this study , the number of blood isolates of e. coli producing extended - spectrum -lactamase ( esbl ) was 614 ( 6.7% ) ; 188 of them ( 30.6% ) were nonsusceptible to amc . when esbl - producing e. coli isolates were excluded from analysis , amc nonsusceptibility increased from 8.4% ( 2003 ) to 14.3% ( 2006 ) (  test for trend 34.39 ; p<0.0001 ) in total isolates ; from 8.2% ( 2003 ) to 14.5% ( 2006 ) (  test or trend 25.23 ; p<0.0001 ) in community - acquired isolates ; and from 8.9% ( 2003 ) to 13.3% ( 2006 ) (  test for trend 6.35 ; p = 0.012 ) in hospital - acquired isolates ( figure 1 ) . the proportion of isolates highly susceptible to amc ( mic < 4 mg / l ) steadily decreased over the study period as follows : 70.2% ( 2003 ) , 70% ( 2004 ) , 64.8% ( 2005 ) , and 57.4% ( 2006 ) (  test for trend 99.36 ; p<0.0001 ) . community consumption of penicillin/-lactamase inhibitors , predominantly amc , increased 34.7% from 2000 to 2006 ( figure 2 ) , whereas total antimicrobial drug consumption remained relatively constant ( 19.6 dids in 2000 compared with 19.1 dids in 2006 ) . after amc , the most used -lactam antimicrobial agents in the community in spain were amoxicillin , cefuroxime , and cefixime ; their consumption did not vary or slightly decreased from 2002 through 2005 ( 6 ) . evolution of consumption of outpatient penicillin/-lactamase inhibitors ( world health organization code j01cr02 ) , spain , 20002006 . the increased amc resistance of e. coli isolates from blood observed in this study is of serious concern from clinical and epidemiologic standpoints because amc is the first - choice antimicrobial treatment for many invasive e. coli infections . increased amc resistance coincided with growing amc consumption at the community level . in urinary infections , previous treatment with amc is a risk factor for the development of amc resistance ( 10 ) . amc resistance mechanisms ( -lactamase overproduction , ampc cephalosporinase hyperproduction , and inhibitor - resistant penicillinases ) ( 11 ) might be favored by strong amc consumption .
to determine the evolution and trends of amoxicillin  clavulanic acid resistance among escherichia coli isolates in spain , we tested 9,090 blood isolates from 42 spanish hospitals and compared resistance with trends in outpatient consumption . 
 these isolates were collected by spanish hospitals that participated in the european antimicrobial resistance surveillance system network from april 2003 through december 2006 .