Antimicrobial susceptibility testing trends and accuracy in the United States. A review of the College of American Pathologists Microbiology Surveys, 1972-1989. Microbiology Resource Committee of the College of American Pathologists.

The ability of the College of American Pathologists Microbiology Surveys subscriber laboratories to perform antimicrobial susceptibility testing accurately has improved slightly since 1984. Currently (1989 surveys), the accuracies for disk diffusion and minimum inhibitory concentration antimicrobial susceptibility testing were 98.2% and 96.1%, respectively. Disk diffusion testing has recently (since 1986) become more popular, along with rapid automated systems, such as the AMS-Vitek System (St Louis, Mo). Rapid tests for beta-lactamase and chloramphenicol acetyltransferase have performed well. Quality control procedures have switched to a cost-effective weekly frequency pattern for nearly 70% of laboratories. Some antimicrobial susceptibility testing problems still exist among anaerobic bacterial methods, procedures for fastidious organisms (Haemophilus, Streptococcus species, Moraxella, pneumococci, gonococci), tests for oxacillin-resistant staphylococci, and the methods for use against nonenteric gram-negative or gram-positive bacilli. Antimicrobial susceptibility testing users subscribing to the College of American Pathologists surveys should strictly follow the National Committee for Clinical Laboratory Standards interpretive and quality control criteria to assure the best performance with the Clinical Laboratory Improvement Act, 1988, compliant College of American Pathologists proficiency sample program.

The identification and antimicrobial susceptibility testing of Neisseria gonorrhoeae, 1980-1987. Results from the College of American Pathologists Microbiology Surveys Program.

The results of the College of American Pathologists (Skokie, III) Microbiology Surveys from 1980 through 1987 indicate subscriber laboratories have continued to improve their ability to identify and test the antimicrobial susceptibility of Neisseria gonorrhoeae. Bacteriology and Comprehensive Surveys participants correctly identified this organism more frequently (95% to 96%) than did the Basic Surveys Laboratories. Neisseria gonorrhoeae samples in mixed cultures were slightly more difficult (3% to 5% decreased accuracy) to identify. Antimicrobial susceptibility testing by the disk-diffusion and beta-lactamase tests were more accurate (98% to 99%) than minimum inhibitory concentration-dilution methods (92%). Currently, most laboratories use the commercially prepared beta-lactamase reagents and the disk-diffusion test. The National Committee for Clinical Laboratory Standards is currently standardizing methods for the susceptibility testing of several antibiotics against gonococci. The College of American Pathologists Microbiology Surveys will continue to monitor participant accuracy for the identification and resistance recognition of this epidemiologically important pathogen.

Latex agglutination test for rubella antibodies: report based on data from the College of American Pathologists surveys, 1983 to 1985.

In the College of American Pathologists (CAP) rubella survey program, 45% of laboratories rely on the latex agglutination (LA) card assay for detecting rubella immunoglobulin G (IgG) antibodies. By using CAP survey data over a 3-year period, we compared LA results with hemagglutination inhibition (HI) and enzyme immunoassay (EIA) results. EIA indices were used to classify results into three categories: nonimmune, EIA index of 0.300 or less; borderline, EIA index of 0.300 to 0.619; and immune, EIA index of 1.700 or greater. There was 91% or more agreement between LA, HI, and EIA for categories i and iii. In category ii, the response from LA users varied, depending on the level of antibody present in the survey samples; at an EIA index of 0.346, 81% reported nonimmune status, whereas at an EIA index of 0.619, 48% reported nonimmune status. Less than 10% indicated borderline status. In testing of samples in the same category, approximately 40%, using the HI method, reported titers of less than 1:8 (nonimmune status). Among EIA users, 97 to 99% regarded the specimens as nonimmune. On analysis of specimens in the borderline category, the LA test showed a pattern of sensitivity and specificity comparable to that reported with the HI technique, whereas the EIA method showed a greater degree of precision. The LA card assay provides a rapid screening test in which LA is read macroscopically, and the procedure differs considerably from the fully quantitative HI and EIA methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotic susceptibility testing accuracy. Review of the College of American Pathologists Microbiology Survey, 1972-1983.

The antibiotic susceptibility testing results for the College of American Pathologists' Microbiology Surveys subscribers for 1981 to 1983 were compared for accuracy and problem areas with earlier data dating back to 1972. Disk diffusion (Kirby-Bauer) test accuracy was 96.3%, 96.4%, and 95.0% for the Bacteriology, Comprehensive, and Basic Surveys participants, respectively. The overall dilution test and automated system (Autobac I) accuracy was 95.8% and 93.8%, respectively. More laboratories (more than 40% of bacteriology and comprehensive laboratories) were using dilution minimum inhibitory concentration tests, usually frozen-form commercial systems. The current test accuracy was comparable with data for previous years, but the Basic Survey subscribers have demonstrated improvement since mid-1981. Several testing problems were identified, principally in the interpretive criteria available in national consensus publications such as the National Committee for Clinical Laboratory Standards M2-A3. Many of these problems have recently been resolved through the cooperation of the National Committee for Clinical Laboratory Standards' subcommittees and the College of American Pathologists' surveys.

Evaluation of enzyme immunosorbent rubella assays.

Rubella enzyme-linked immunosorbent assays [( EIAs] Abbott Laboratories) were compared with hemagglutination inhibition methods in a national survey of clinical laboratories. Rubella EIAs demonstrated greater interlaboratory precision in screening for antibodies and better agreement among participants in quantification of antibody levels. From the viewpoint of interlaboratory surveys, EIA is well suited for routine use in clinical laboratories. The requirement for proper standardization of EIA was discussed.

Special topics in antimicrobial susceptibility testing: test accuracy against methicillin-resistant Staphylococcus aureus, pneumococci, and the sensitivity of beta-lactamase methods.

Three contemporary problems in antimicrobial susceptibility testing were assessed by the CAP-Microbiology Surveys Program in 1982. A penicillin-resistant Streptococcus pneumoniae was categorized correctly as resistant by nearly 78% of Infectious Disease Survey subscribers. This rate compares with a 15% accuracy in the 1981 Surveys challenge, and all results reported from the NCCLS recommended 1 microgram oxacillin screening test correctly found penicillin resistance. Further improvement in the microbiology laboratories' ability to recognize pneumococcal penicillin resistance is critical to good patient care. A methicillin-resistant Staphylococcus aureus (MRSA) strain was assessed accurately by 96.8% of NCCLS disk diffusion test users (methicillin, nafcillin, and oxacillin disks). The microdilution broth method using methicillin as the representative of the penicillinase-stable penicillins performed well. Only nafcillin and oxacillin broth microdilution tests and the automated MIC methods had reduced accuracy. Automated systems also failed to recognize an associated erythromycin resistance in the MRSA strain. Suggestions for improved microdilution test accuracy are made. Three survey challenges have evaluated the sensitivity and specificity of commercial and other beta-lactamase test methods. The false-positive rates for staphylococci range from 3.9 to 4.5%. The false-negative results on a Haemophilus paraphrophilus (beta-lactamase producer) were highest for the iodometric technic (8.7%) and lowest for the chromogenic cephalosporins (1.9%) such as nitrocefin and PADAC. Recommendations for their more limited use in generally emergent clinical settings are offered.

Evaluation of assays for the detection of antibodies to rubella. A report based on data from the College of American Pathologists Surveys of 1982.

Data from laboratories participating in the College of American Pathologists Surveys in 1982 provided information on the trends in testing for antibodies to rubella. Methods used by participants included: passive hemagglutination, 29%; latex agglutination card assay test, 25%; hemagglutination inhibition, 19%; enzyme immunosorbent assays, 13%; indirect fluorescent antibody assays, 11%; and radioimmunoassay, 3%. The results from these methods generally agreed well with the standard HI test, particularly for detection of immunity in negative and strongly positive samples. Laboratories should use caution, however, that the tests they use give satisfactory results with low titered sera. Compared to laboratories using the one to three-day-old chick cells with Heparin-MnCl2 for HI, laboratories using Human O Cells tended to get higher titers, and laboratories using Fixed Chick cell or Kaolin methods tended to get lower titers.

Contemporary quality control practices for antimicrobial susceptibility tests: a report from the microbiology portion of the College of American Pathologists (CAP) surveys program.

The evaluation of quality control (QC) practices from the College of American Pathologists (CAP) Microbiology Surveys demonstrates a trend away from daily controls similar to that first noted in 1980. Previous recommendations for more relevant cost-containment oriented weekly QC procedures are discussed, and the 1982 CAP Surveys statistics confirm earlier comparability between the daily and weekly QC participant groups. Each QC practice subgroup (daily or weekly) had nearly identical mean disk inhibitory zone diameters, and the performance accuracy on two 1982 challenge strains were very similar. Generally, disk zone diameter from those laboratories using weekly QC were smaller, but the frequency of minor and major (false-resistant) errors was only slightly increased. The authors recommend the conversion to weekly QC of disk or dilution antimicrobial susceptibility tests after an acceptable daily QC performance has been established (See criteria in discussion).

Interlaboratory performance of disk agar diffusion and dilution antimicrobial susceptibility tests, 1979-1981. A summary of the microbiology portion of the College of American Pathologists (CAP) surveys.

The antimicrobial susceptibility test results of the 1979-1981 College of American Pathologists (CAP) Microbiology Surveys are summarized for the disk diffusion and dilution test methods. Improved interpretive accuracy (97.5%) was detected for the Special Bacteriology participants compared with those reported for 1972 and 1977-1978. The performance accuracy rates for the Comprehensive and Basic Surveys subscribers was 95.8% and 93.7%, respectively (all surveys accuracy rates was 95.2% from 196,775 responses). The dilution methods were graded since 1980 and showed an acceptable or good performance rate of 98.0%. Most reported MICs were from commercial systems, especially those performed in frozen broth microdilution systems. Eighteen per cent of all susceptibility tests are now reported as MICs. Quality control data shows a trend away from costly daily control practices without compromise of test accuracy. Several problem areas continue to plague these methods: (1) poor predictive value of disk results for enterococci; (2) availability of low potency disks with suboptimal accuracy rates, e.g., the 50 micrograms carbenicillin disk; (3) the release of more new drugs requiring individual testing beyond the capacity of the test systems; (4) vague recommendations for reporting and testing certain bacterial species, e.g., methicillin-resistant staphylococci and penicillin-resistant pneumococci; and (5) the lack of contemporary modification in FDA package insert quality control and interpretive criteria guidelines that might reflect new test or therapeutic information. Overall, the 1979-1981 surveys results show improved performance to a high level of predictive and interpretive accuracy among all subscriber groups coupled with a shift toward the more informative quantitative dilution methodologies.

Comparison of concentration procedures for detection of Schistosoma mansoni eggs in a CAP Parasitology Survey specimen.

A comparison of concentration procedures for the detection of Schistosoma mansoni is presented. Ethyl-acetate or formalin-ether centrifugal sedimentation technics are not only the most commonly used, they also lead to more accurate identification of the organism's eggs.

The ability of participant laboratories to detect penicillin-resistant Pneumococci. A report from the microbiology portion of the College of American Pathologists (CAP) surveys.

To assess the ability of clinical laboratories to identify penicillin-resistant Streptococcus pneumoniae, a challenge sample was distributed to CAP Special Bacteriology surveys participants in 1981. Their performance was excellent (greater than 99%) for organism identification, but less than 15% of surveys subscribers that use the standardized disk diffusion test detected penicillin resistance. The recommendations of the NCCLS M2-A2S for 1-microgram oxacillin disk screening are discussed. The screening and dilution tests for detecting drug resistant S. pneumoniae seem to be accurate and the use of other disks, such as methicillin and nafcillin, also appear efficacious. Due to the clinical frequency of serious pneumococcal disease, all microbiology laboratories should be applying these screening procedures to appropriate patient isolates.

Evaluations of antimicrobial susceptibility test proficiency by the College of American Pathologists Survey program. A clarification of quality control recommendations.

The College of American Pathologists (CAP) Interlaboratory Survey Program in microbiology was reviewed for quality control practices of the Special Bacteriology participants (907 laboratories) using the disk agar diffusion antimicrobial susceptibility test method. Data from a questionnaire was compared to performance results on two well recognized quality control strains, e.g., Pseudomonas aeruginosa ATCC 27853 and Streptococcus faecalis ATCC 29212. The results show no significant difference in survey performance between those participants using daily controls (97.78 and 96.99% acceptable results) and those using weekly controls (97.33 and 96.67% acceptable results). Similarly, the number of tests done per work day had little influence on the reported mean zone diameter and subscriber results were comparable to published means from the reference literature. Recommendations are made to use weekly quality control after test proficiency has been repeatedly demonstrated by daily or batch control results. More frequent testing would be required if any reagent lot were replaced or altered. Comparable data on quality control intervals of greater than 7 days was not evaluated due to small numbers of test results.

Prevalence of antibodies to Legionnaires' disease. A seroepidemiologic survey of Michigan residents using the hemagglutination test.

The indirect fluorescent antibody test and a microhemagglutination technique detected antibodies in human sera to Legionnaires' disease antigen about equally. Since the hemagglutination technique was simpler, more rapid, and less expensive, we used it to ascertain the prevalence of antibody in 1200 sera from apparently healthy, nonhospitalized Michigan residents. Prevalence was analyzed by age, sex, geographic location (county or residence), and season of the year. There was a significant difference in prevalence between seasons: 91 of 600 sera (15.2%) from February to March 1978 had a titer equal to or greater than 1.16, contrasted with 179 of 600 sera (29.8%) from August to September 1978. This difference was independent of age and sex. There was no significant difference by geographic location, sex, or age except for decreased prevalence for persons 60 years or older.