Diagnostic electron microscopy is still a timely and rewarding method

Background: Parallel to its technical development starting in the 1930s, el ectron microscopy (EM) became an important tool in basic and clinical virol ogy. First utilized in the rapid diagnosis of smallpox, it developed to a d iagnostic routine in the early 1960s using the negative staining technique. ERI was applied to infected cell-cultures and also to 'dirty' specimens in cluding urine, feces, vesicle fluid, liquor. With the implementation of mol ecular biological and genetic techniques, the use of diagnostic EM decrease d. Objectives: (1) To give a perspective on future indications and possible uses by discussing the past and the present of diagnostic EM, (2) To descr ibe the system of External Quality Assessment on EM virus diagnosis (EQA-EM V) established in 1994 by our laboratory and its achievements. Study design : EQA-EMV is run to evaluate, to confirm and to improve the quality of diag nostic EM. Two different types of specimen are sent out: (1) prepared grids to assess and train the diagnostic skills of the participants, (2) stabili zed virus particle suspensions to assess preparation efficiency. Results: D iagnostic EM differs from other diagnostic tests in its rapidity and its un directed 'open view'. To emphasize these advantages, the indications for di agnostic EM are discussed, fundamental for a continuing future adaptation. Besides appropriate techniques, quality control measures are required to ac hieve and keep high diagnostic standards. The results from 6 years of EQA-E MV are presented. Conclusions: In the history of diagnostic EM in virology, a change in use has been seen. Starting in the 1990s:and coincident with t he broad introduction of 'modern' diagnostic techniques, the number of EM d iagnostic labs has decreased considerably-in spite of the obvious advantage s of this technique. To guarantee the continuing performance of diagnostic EM in the future, EQA runs have to be performed as with other techniques in the diagnostic armament. The growing number of participants and participat ing countries indicates an interest in as well as a need for this program. (C) 1999 Elsevier Science B.V. All rights reserved.