Quality Control in Microbiology: A Review and Bibliography

Internal quality assurance in a clinical virology laboratory. I. Internal quality assessment

AIMS

In April 1991 an internal quality assessment scheme (IQAS) was introduced into the virology section of the Clinical Microbiology and Public Health Laboratory, Cambridge. The IQAS was established to identify recurring technical and procedural problems, to check the adequacy of current techniques, and to calculate the frequency of errors.

METHODS

Between April 1991 and December 1993, 715 anonymous clinical serum samples were submitted to the laboratory to test 3245 individual procedures of diagnostic viral serology.

RESULTS

A total of 485 (14.9%) procedural and 61 (1.9%) technical discrepancies were observed, the technical discrepancies mainly being recorded in complement fixation tests. Twenty two (0.7% of total procedures) of the technical discrepancies were diagnostically significant.

CONCLUSIONS

Evaluation criteria developed with the introduction of IQAS to viral serology, and technical and procedural discrepancies are assessed. As yet, IQAS has not been introduced to other sections of the diagnostic virology laboratory (virus isolation, electron microscopy, immunofluorescence, and enzyme linked immunosorbent assays for viral and chlamydial antigens).

Laboratory identification and sensitivity testing of yeast isolates

Methods used for identification and sensitivity testing of yeasts are presented. Identification depends on both morphologic features and biochemical characteristics. The germ tube test is a simple test for the identification of the commonest yeast pathogen, Candida albicans. Species not identified by this method can be identified by means of several other tests, the most important being the carbohydrate assimilation test. Several kits are commercially available and most appear to be satisfactory. Antifungal susceptibility tests are not standardized, and results are often subject to considerable variation. Until improved methods are developed, it might be advisable that smaller laboratories only do a preliminary screening test for flucytosine susceptibility and, if indicated, also for amphotericin B susceptibility. Important isolates should be sent to laboratories with a special interest in antifungal susceptibility testing for more extensive testing.