Uses and Pitfalls
Beyond Hot Topic is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.
The following questions were submitted by viewers and answered by the presenter, Bobbi Pritt, MD, Consultant in the Clinical Microbiology Division, Associate Professor of Laboratory Medicine and Pathology and Microbiology, and Director of the Clinical Virology and Parasitology Laboratory at Mayo Clinic in Rochester, MN.
Questions are presented as submitted (unedited).
Do we need a good amount of colony growth of a virus before using it for antiviral susceptibility testing?
Antiviral susceptibility testing using either molecular or culture-based techniques performs best when there is ample virus/viral nucleic acid present. However, even a small amount of virus may be sufficient and so it may still be worthwhile to attempt the susceptibility testing.
Is the list of viruses and the preferred method of testing available as a print-out?
While we don’t offer a handout of viruses and preferred testing method, the Hot Topic presentation is available as a handout, and similar lists have been published. I would recommend the following sources:
Diagnosis of Infections Caused by Viruses, Chlamydia, Rickettsia, and Related Organisms, In Koneman’s Color Atlas and Textbook of Diagnostic Microbiology, 6th Edition, Chapter 23, pages 1370-1371.
Landry et al. Algorithms for Detection and Identification of Viruses. In Manual of Clinical Microbiology, 10th Edition. Volume 2, pages 1297-1301.
Given the potential for severe, life-threatening HSV encephalitis, I would strongly recommend the use of HSV PCR rather than culture if PCR is available and the turn-around-time is as good as or faster than culture.
When we detect reproducible, unusual CPE, we refer the isolate to our state laboratory for additional testing. The state and local health laboratories often have additional resources at their disposal, beyond what is available at the local laboratory level. They can also send the isolate to the Centers for Disease Control and Prevention (CDC) if necessary. It is important to perform additional workup in cases of unusual CPE since this may indicate the presence of a new emerging virus (eg SARS) or unusual virus (eg measles). The additional resources available at the state health lab and/or CDC are essential for identifying these agents.
If methods such as PCR are so much better, why is Mayo still using tube culture?
We have switched most of our testing over to PCR due to its superior performance characteristics and faster turn-around-time. However, as I mentioned in my presentation, there are still some situations in which culture has its uses. As a reference lab serving the United States, we have chosen to continue our traditional tube culture so that we can best serve our patient population, even in unusual situations. Smaller laboratories, however, may choose to discontinue culture if routine testing needs can be met with molecular methods.