External quality assessment of antimicrobial susceptibility testing in Europe.

Comparability of results of antimicrobial susceptibility testing is essential for resistance surveillance studies. As different methods may be used in different countries, there may be particular problems with international comparisons of resistance rates. Data from external quality assessment (EQA) surveys participated in by laboratories from several European countries allow comparison of performance between countries. In this study, success rates with organism-antimicrobial agent combinations known to be difficult to test were examined. With penicillin resistance in pneumococci; vancomycin and high-level gentamicin resistance in enterococci; ampicillin, co-amoxiclav and chloramphenicol resistance in Haemophilus influenzae and methicillin resistance in staphylococci there were differences between countries in success rates for discrimination of resistant strains. This study suggests that differences between countries in rates of resistance for some organism-antimicrobial agent combinations should be interpreted with caution. International EQA is useful in the demonstration and clarification of such differences.

Sistema internacional de la OMS para evaluar la calidad de las pruebas detectoras de anticuerpos contra el VIH: resultados de la segunda distribución de sueros / WHO international quality assessment scheme for HIV antibody testing: results from the second distribution of sera

El sistema internacional de la OMS para evaluar la calidad de las pruebas detectoras de anticuerpos contra el virus de la inmunodeficiencia humana (VIH) se estableció para controlar la calidad de la labor desempeñada por los laboratorios en este campo. Después de la distribución de unos cuantos especímenes con fines experimentales a comienzos de 1989, una segunda distribución se hizo en febrero de 1990. En total se enviaron 20 especímenes de suero, 10 con anticuerpos contra el VIH-1, a 103 laboratorios en las seis regiones de la OMS. Se pidió a los participantes que aplicaran a los especímenes sus pruebas estandarizadas y que para cada uno notificaran a la OMS los resultados obtenidos con cada tipo de prueba diagnóstica y su interpretación con respecto ala presencia o ausencia de anticuerpos contra el VIH. En lo concerniente a los especímenes con anticuerpos, los resultados se consideraron positivos en 98,2 por ciento de los casos e indeterminados en 1,8 por ciento; no se notificaron resultados negativos falsos. En el caso de los especímenes sin anticuerpos, 90,3 por ciento de los resultados se consideraron negativos, 1,3 por ciento positivos y 8,4 por ciento indeterminados. La mayor parte de los informes con resultados indeterminados correspondieron a un espécimen en particular. Se uso una amplia variedad de pruebas diagnósticas solas y combinadas. Si se tienen en cuenta los resultados técnicos, más que su interpretación, la confiabilidad de las pruebas fue muy buena en lo que respecta a los especímenes positivos: 99,5 por ciento de los resultados registrados fueron positivos, 0,17 por ciento negativos y 0,34 por ciento indeterminados. Los especímenes negativos se asociaron con un mayor número de errores: 93,5 por ciento de los resultados registrados fueron negativos, 3,5 positivos y 3 por ciento indeterminados. Sin embargo, 61 por ciento de los resultados positivos falsos e indeterminados que se obtuvieron al aplicar las pruebas a especímenes negativos correspondieron a dos especímenes solamente. La prueba western blot dio resultados muy variados, a los que se aplicaron distintos criterios de interpretación

Sistema internacional de la OMS para evaluar la calidad de las pruebas detectoras de anticuerpos contra el VIH: resultados de la segunda distribución de sueros / WHO international quality assessment scheme for HIV antibody testing: results from the second distribution of sera

El sistema internacional de la OMS para evaluar la calidad de las pruebas detectoras de anticuerpos contra el virus de la inmunodeficiencia humana (VIH) se estableció para controlar la calidad de la labor desempeñada por los laboratorios en este campo. Después de la distribución de unos cuantos especímenes con fines experimentales a comienzos de 1989, una segunda distribución se hizo en febrero de 1990. En total se enviaron 20 especímenes de suero, 10 con anticuerpos contra el VIH-1, a 103 laboratorios en las seis regiones de la OMS. Se pidió a los participantes que aplicaran a los especímenes sus pruebas estandarizadas y que para cada uno notificaran a la OMS los resultados obtenidos con cada tipo de prueba diagnóstica y su interpretación con respecto ala presencia o ausencia de anticuerpos contra el VIH. En lo concerniente a los especímenes con anticuerpos, los resultados se consideraron positivos en 98,2 por ciento de los casos e indeterminados en 1,8 por ciento; no se notificaron resultados negativos falsos. En el caso de los especímenes sin anticuerpos, 90,3 por ciento de los resultados se consideraron negativos, 1,3 por ciento positivos y 8,4 por ciento indeterminados. La mayor parte de los informes con resultados indeterminados correspondieron a un espécimen en particular. Se uso una amplia variedad de pruebas diagnósticas solas y combinadas. Si se tienen en cuenta los resultados técnicos, más que su interpretación, la confiabilidad de las pruebas fue muy buena en lo que respecta a los especímenes positivos: 99,5 por ciento de los resultados registrados fueron positivos, 0,17 por ciento negativos y 0,34 por ciento indeterminados. Los especímenes negativos se asociaron con un mayor número de errores: 93,5 por ciento de los resultados registrados fueron negativos, 3,5 positivos y 3 por ciento indeterminados. Sin embargo, 61 por ciento de los resultados positivos falsos e indeterminados que se obtuvieron al aplicar las pruebas a especímenes negativos correspondieron a dos especímenes solamente. La prueba western blot dio resultados muy variados, a los que se aplicaron distintos criterios de interpretación

Publicado en inglés en el Bull. Pan Am. Health Organ. 70(5), 1992

Antimicrobial susceptibility testing of enterococci: results of a survey conducted by the United Kingdom National External Quality Assessment Scheme for Microbiology.

Six strains of enterococci were distributed to participants in the United Kingdom National External Quality Assessment Scheme for Microbiology with a request that they be tested for susceptibility to ampicillin/penicillin and vancomycin and for high-level resistance to gentamicin. More than 98% of laboratories correctly reported the resistant strains as resistant to penicillin and ampicillin. However, there was a poorer correlation for the susceptible strains, with only 1-6% and 69-83% of laboratories reporting the strains as susceptible to penicillin and ampicillin respectively. Those laboratories which used 5-25 micrograms ampicillin discs or breakpoint methods reported proportionally more results correctly for the susceptible strains than those using 2 micrograms discs. Participants using Escherichia coli or an enterococcus as a control and those not using a control at all were more likely to report ampicillin-susceptible strains correctly than those using Staphylococcus aureus NCTC 6571 (Oxford strain). For vancomycin-susceptible and high-level vancomycin-resistant strains, 93-96% and 96-99% of reports respectively were correct. For the low-level vancomycin-resistant strains, only 50-54% of reports were correct. Participants using a 5 micrograms vancomycin disc reported proportionally more of the low-level resistant strains correctly than those using 10, 20, 25, 30 or 100 micrograms discs. Participants not using controls were proportionally more likely to report the low-level resistant strains as susceptible than those using an enterococcus or S. aureus NCTC 6571 as a control. For the high-level gentamicin-resistant (HLGR) strains, 96-98% of reports were correct. Depending on the strain, between 12% and 41% of participants also reported high-level resistance for the strains which were not HLGR. Those using low-content discs (< or = 30 micrograms) and breakpoint or MIC methods were more likely to report strains which were not HLGR as HLGR than those using high-content discs. Those using an enterococcus as a control were less likely to report strains which were not HLGR as HLGR than those using either S. aureus NCTC 6571 or E. coli as a control and those not using a control.

Parasitology: United Kingdom National Quality Assessment Scheme.

AIMS: To assess the results from parasitology laboratories taking part in a quality assessment scheme between 1986 and 1991; and to compare performance with repeat specimens. METHODS: Quality assessment of blood parasitology, including tissue parasites (n = 444; 358 UK, 86 overseas), and faecal parasitology, including extra-intestinal parasites (n = 205; 141 UK, 64 overseas), was performed. RESULTS: Overall, the standard of performance was poor. A questionnaire distributed to participants showed that a wide range of methods was used, some of which were considered inadequate to achieve reliable results. Teaching material was distributed to participants from time to time in an attempt to improve standards. CONCLUSIONS: Since the closure of the IMLS fellowship course in 1972, fewer opportunities for specialised training in parasitology are available: more training is needed. Poor performance in the detection of malarial parasites is mainly attributable to incorrect speciation, misidentification, and lack of equipment such as an eyepiece graticule.

WHO international quality assessment scheme for HIV antibody testing: results from the second distribution of sera.

The WHO international quality assessment scheme for human immunodeficiency virus (HIV) antibody testing has been established to monitor the quality of laboratory performance in testing for antibodies to HIV. Following a small trial distribution of specimens early in 1989, the second distribution was made in February 1990. A total of 20 specimens of sera, 10 of which contained antibodies to HIV-1, were sent to 103 laboratories located in the six WHO Regions. Participants were asked to test the specimens using their routine methods and to report to WHO their findings on each specimen for each diagnostic assay used and their interpretation of the HIV antibody status of each specimen. For the antibody-positive specimens, 98.2% of the results were interpreted as positive and 1.8% as indeterminate; no false-negative interpretations were reported. For the antibody-negative specimens, 90.3% of the results were interpreted as negative, 1.3% as positive, and 8.4% as indeterminate. Most of the indeterminate reports were associated with one particular specimen. A wide variety of diagnostic assays and combinations of assays were used. In terms of the technical results obtained rather than their interpretation, the assays appeared extremely reliable for the positive specimens, with 99.5% of assay results being recorded as positive, 0.17% as negative, and 0.34% as indeterminate.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of chloramphenicol resistance in Haemophilus influenzae.

An average of 358 (13%) of United Kingdom laboratories failed to detect resistance to chloramphenicol in strains of Haemophilus influenzae distributed by the United Kingdom National External Quality Assessment Scheme for Microbiology. Clear associations between methods used and results obtained show that error rates are minimised by the use of low content (10 micrograms) disc and a sensitive control strain of H influenzae.

World Health Organization quality assessment programme on HIV testing.

A serum panel comprising 19 samples of known (five positives and 14 negatives) but undisclosed HIV-1-antibody content was distributed to 30 national reference laboratories for HIV serology. In order to simulate normal circumstances of referral, participants were asked to test the panel for HIV-1-antibody status using their normal procedures. Results of testing were returned by 28 participants. There were great variations in the number and combinations of tests used. The number used ranged from one to five assays per laboratory and none of the 24 laboratories using two or more tests employed the same combination. A high average success rate of 99% was seen with the positive samples. More errors occurred with the negative samples, with an average of 87% correct negative reports. Only four of the 14 negative specimens were reported as negative by all participants.

Mycology quality assessment: United Kingdom national scheme.

A mycology quality assessment scheme introduced in 1986 was assessed: 289 laboratories participated in the scheme, and six distributions, each containing four specimens, were made. Levels of performance varied considerably among participating laboratories: performance was highest with the commoner organisms distributed, but some laboratories, encouragingly, achieved a consistently high level of species identification. A questionnaire distributed to participants showed that a wide range of methods are commonly used, some of which are contrary to good practice. As the scheme continues, selection of organisms considered to be relevant and of use to participants will become difficult.

Antimicrobial susceptibility testing of Streptococcus pneumoniae: quality assessment results.

Six strains of Streptococcus pneumoniae were distributed to 405 United Kingdom laboratories who were asked to test the susceptibility of the strains to penicillin, tetracycline, chloramphenicol and erythromycin and to provide details of methodology to test the standards of susceptibility testing. High error rates were seen only in failure to detect moderate resistance to penicillin (12%) and resistance to chloramphenicol (16%). Increased error rates were associated with several methods or practices. These included the use of certain culture media; failure to standardise the inoculum; inoculation by loop rather than by swab; failure to use control organisms; failure to measure zone sizes; the use of discs containing a high content of penicillin to test susceptibility to penicillin, and the use of high content discs for testing erythromycin, tetracycline, and chloramphenicol.

Antimicrobial susceptibility testing of Neisseria gonorrhoeae: a trial organised as part of the United Kingdom national external quality assessment scheme for microbiology.

Six strains of Neisseria gonorrhoeae were distributed to 411 United Kingdom laboratories who were asked to test the susceptibility of the strains to penicillin, cefuroxime, tetracycline and spectinomycin and to test for production of beta-lactamase. Details of methods used were requested by means of a questionnaire. The number of reports recording sensitive strains as resistant was 5% for penicillin, 0.7% for cefuroxime, 3% for tetracycline and 4% for spectinomycin. The number of reports recording resistant strains as sensitive was 7% for penicillin (0.2% with beta-lactamase producing strains, 20% with non-beta-lactamase producing strains), 96% for cefuroxime, 76% for tetracycline and 8% for spectinomycin. There was an association between greater error rates and the use of high content discs for testing tetracycline, the use of low content discs for testing spectinomycin, failure to dilute the inoculum, and use of acidimetric methods rather than methods that use a chromogenic cephalosporin for detecting beta-lactamase.

Antimicrobial susceptibility testing of Haemophilus influenzae: trial organised as part of United Kingdom national external quality assessment scheme for microbiology.

Six strains of Haemophilus influenzae were distributed to 417 United Kingdom laboratories who were asked to test susceptibility of the strains to ampicillin, augmentin, tetracycline, chloramphenicol, and trimethoprim and to test for beta lactamase production. Laboratories were also asked to provide details of their methods by completing a questionnaire. The incidence of reports recording sensitive strains as resistant was 8% (ampicillin), 7% (augmentin), 3% (tetracycline), 1% (chloramphenicol), and 12% (trimethoprim). The incidence of reports recording resistant strains as sensitive was 9% (ampicillin), (2% with beta lactamase producing strains, 24% with non-beta lactamase producing strains), 51% (augmentin), 10% (tetracycline), 20% (chloramphenicol), and 3% (trimethoprim). High error rates were associated with several methods or practices. These included use of general purpose growth media rather than susceptibility testing media and failure to add lysed blood to the media when testing trimethoprim susceptibility; standardise the inoculum; use suitable control strains; and the use of high content discs for testing chloramphenicol, tetracycline, and ampicillin.

Preparation of simulated clinical material for bacteriological examination.

The preparation of mixtures of bacteria to mimic the flora found in pathological material is described. Such mixtures are useful for teaching, for practical examinations, for quality control of media and methods and for use in quality assessment schemes. The design of suitable mixtures is discussed and the stabilities of mixtures in transport media and in freeze-dried preparations are compared. Transport media provide short term storage for periods of several weeks and, with various modifications, are moderately successful with some, but not all, quite delicate pathogens. Freeze-drying however, provides greater stability over periods of months, allows preservation of delicate pathogens and is the preferred method where specimen quality is important.

United Kingdom scheme for external quality assessment in virology. Part I. General method of operation.

Developments in the United Kingdom national external quality assessment scheme for virology are described. There are about 198 participants (170 in the UK) who are enrolled for examination of any or all of five categories of specimen (distribution types). These are detection of rubella antibody (128 UK participants), detection of hepatitis B surface antigen (130 UK participants), general virus serology (86 UK participants), virus identification (85 UK participants), and electron microscopy (56 UK participants). Specimens of a sixth category (rubella IgM antibody), not yet formally established, have also been distributed to 67 UK participants. Specimens in each distribution type are sent out once or twice a year, and, except for rubella IgM antibody, participants have been given a score of 2, 1, 0 or -1 marks for their reports on each specimen. Their cumulative scores and performance ratings are calculated retrospectively over a 12 month period for each distribution type separately and for combined distributions. The performance rating is defined by the number of standard errors by which the individual's cumulative score differs from the mean for all participants and carries a + or - sign depending on whether the cumulative score lies above or below the mean. Performance ratings have been found generally to be close to the mean in rubella serology and detection of hepatitis B surface antigen but are more variable in virus identification and electron microscopy. Ratings of less than -1.96 are considered to be significantly worse than average and to constitute poor performance.