Use of Local Community Hospital Data for Surveillance of Antimicrobial Resistance
We sought to determine whether antimicrobial susceptibility data from a nonteaching community hospital could be used to detect statistically significant local increases in resistance among Streptococcus pneumoniae over a 5‐year period. Minimum inhibitory concentrations (MICs) of penicillin and ceftriaxone from 1997‐1998 were compared with those from 2000‐2001. MICs of penicillin and ceftriaxone for organisms collected in a nonteaching community hospital in central Illinois were used for analysis. The hospital has 224 beds and a catchment area of approximately 40 miles. There were significant increases in MICs of penicillin and ceftriaxone between 1997‐1998 and 2000‐2001. The MIC of penicillin increased from 0.042 to 0.121 μg/mL (
; 95% confidence interval, −1.713 to −0.388), and the MIC of ceftriaxone increased from 0.028 to 0.071 μg/mL (
; 95% confidence interval, −1.353 to −0.188). There were no significant changes in the percentage of S. pneumoniae isolates that were resistant, intermediate, or susceptible to penicillin and ceftriaxone. MIC data from a community hospital can be used to detect local increases in the rate of resistance before antibiogram data show significant changes. This information is important for demonstrating to physicians the need to review local antibiotic use in the attempt to slow the development of resistant organisms in the community.
Received September 14, 2005; accepted January 26, 2006; electronically published February 24, 2006.
The Centers for Disease Control and Prevention (CDC) has listed antibiotic resistance as one of the world’s most pressing public health problems.1 Increased prescribing and inappropriate use of antibiotics have facilitated the spread of resistant pathogens at a rate at which that they would not have spread otherwise.2‐4 Surveillance of susceptibility patterns conducted by the CDC has shown large variations throughout the country, which make the data less effective in demonstrating the best antimicrobial agent for use in a local area.5,6 Because of the overall increase in antibiotic resistance and the variation in resistance patterns by geographic location, effective affordable strategies for the surveillance of these organisms are needed at the local level to monitor trends in susceptibility levels and to guide empirical therapy.7
The data from the CDC were collected from large teaching hospitals.5 This information may not be applicable to smaller, nonteaching, community‐based hospitals, because of differences in practices.8‐12 This problem is further exacerbated by the lack of infectious diseases consultants in smaller nonteaching hospitals.13 These differences in practice make hospital‐specific data to monitor local susceptibility levels immensely important for the proper use of antibiotics. Several studies have found that summaries of local patterns of susceptibility (ie, antibiograms) provide useful information for the empirical treatment of infections.14‐17 However, antibiograms cannot be used to detect changes in the minimum inhibitory concentration (MIC) through each susceptibility category (ie, susceptible, intermediate, and resistance).17 Analysis of MICs would provide local information concerning the trends within each level of susceptibility. These trends in decreasing susceptibility according to MICs have not been previously studied as a tool in a community hospital for the customization of antibiotic use to address the local resistance problem. The present study examined the use of MICs from a community hospital in the Midwest to determine whether trends in resistance could be detected before antibiogram data changed, using a 5‐year period as the time frame of analysis.
Methods
The MICs were for organisms collected in a nonteaching community hospital in central Illinois that has 224 beds and a catchment area of approximately 40 miles. The data collected from January 2000 through December 2001 (
) were compared with data from a previous study conducted during 1997‐1998 (
). All testing was performed before the changes in break points for the susceptibility categories were made.18 Streptococcus pneumoniae was used as the test organism because of the rapidly increasing resistance seen in the organism during the mid‐to‐late 1990s.19 The Etest (AB Biodisk) was used to test susceptibility of the organisms to penicillin and ceftriaxone in both studies.20,21 The gradient of MICs covered a discrete concentration range of either 0.016 to 256 μg/mL for penicillin or 0.002 to 32 μg/mL for ceftriaxone. MICs reported for S. pneumoniae from both the inpatient and outpatient population and from any anatomical site were included in the study. The identification of the organisms as S. pneumoniae was verified by the optochin susceptibility test and the bile solubility test.22
Because of the large range of MICs, geometric means were determined for the MICs of each antibiotic. The use of geometric means has been found previously to be a more accurate measurement of the central tendency of MICs.23
The MICs were used to categorize the organisms as susceptible, intermediate, or resistant to the antibiotics. These categories are determined according to standards set by the Clinical and Laboratory Standards Institute (formerly referred to as the NCCLS) for analysis.24 The categories for the 2 groups were analyzed by the χ2 test for statistical difference. The 2 groups were also compared for significant increases in overall mean MICs for penicillin and ceftriaxone and the increase in mean MICs within susceptible, intermediate, and resistant categories by the Student's t test.
Results
In the present study, 100 specimens were collected. A total of 52 specimens were collected in the previous study. The patients ranged in age from less than 1 year to 93 years. The specimens obtained for culture were primarily blood and sputum. There was no statistical difference between the 2 groups with respect to age and types of specimens from which organisms were recovered.
The susceptibility patterns for both groups of organisms revealed that, although there was not a statistical difference between the groups, there was a trend toward an increasing rate of resistance for both of the antibiotics tested. For penicillin, the percentage of susceptible organisms decreased from 63.5% to 51%, and for ceftriaxone, the percentage decreased from 94.2% to 87%. The analysis of penicillin revealed an increase from 32.7% to 37% in the percentage of pathogens in the intermediate group and an increase from 3.8% to 12% in the percentage of pathogens in the resistant group. The data for ceftriaxone resistance revealed an increase from 5.8% to 13% in intermediate resistance during the testing period.
The geometric means for the MICs of each antibiotic for each group were determined. The MIC of penicillin increased from 0.042 to 0.121 μg/mL (
; 95% confidence interval, −1.713 to −0.388), and the MIC of ceftriaxone increased from 0.028 to 0.071 μg/mL (
; 95% confidence interval, −1.353 to −0.188). To expand the analysis of MICs, the parameters of the susceptibility categories were analyzed to determine whether there was a shift in mean MICs within the categories. The increase of MICs within the susceptibility category from 0.012 to 0.021 μg/mL for penicillin (
; 95% confidence interval, −0.779 to −0.409) and from 0.023 to 0.040 μg/mL for ceftriaxone (
; 95% confidence interval, −1.110 to −0.006) revealed a trend of decreasing susceptibility, even though there was insufficient change to place the organisms into the intermediate category.
Discussion
It has previously been noted that use of a local monitoring system may allow for better control of the prescribing of antibiotics, to decrease the pressure that induces the development of resistance in different bacteria.7,17,25‐32 The present study has shown that the analysis of MICs allows community hospitals to use small numbers of organisms to detect trends in susceptibility patterns before changes in antibiogram data are observed. Early detection of increasing susceptibility, even before antibiogram changes are noted, will allow time to allow antibiotic prescribing patterns and halt the progression of resistance to a particular class of antibiotics.
The need to provide physicians with current information about trends in local susceptibility patterns is crucial for quality patient care. This information can be provided by local community hospitals in statistically significant form through information already available, with little additional analysis and reporting. These data need to be incorporated in the continuing‐medical‐education system for physicians. In the absence of an infectious diseases specialist, a physician leader needs to be identified within the medical community to promote the use of this information. To provide evidence that this information will change prescribing patterns, a prospective study needs to be conducted in a community hospital after a physician education program has been implemented.
Acknowledgment
I thank the Institutional Review Board and Microbiology Department of the BroMenn Regional Medical Center, Normal, Illinois, for their help in securing the specimens for this project.
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