Are cells with a high passage number sensitive in virus isolation studies?

Hi,
I was wondering, is it really a good idea to use cell cultures at a high passage number for  virus isolation from clinical specimens?  What would be an appropriate stage of cell passage for virus isolation (in general)?  Would greatly appreciate your comments.

This really depends on the cell line and virus in question.
Some cell lines do not respond to virus at a low passage, and cell lines tend to have a finite passage level after which they will not grow well themselves let alone take up virus.

I would suggest cell cultures that are a couple of passages old at least before testing with virus but beyond that it depends on the lifespan of the cell line in question. Perhaps if you had a known virus culture, you could trial it on the cells at different passages to see when/where the  virus is best detected.

What virus are you attempting to isolate, and on which cells?

Thanx for that; I have had experiences with rabies virus and BHK-21 cells when the virus adpated for growth in the same cell line would give only low yields sometimes (the passage numbers of the cells I had were well over 100).  This is when I was preparing virus stock for my experiments.  The cells would grow well at high passage numbers, though.
At other times, I have seen similar issues with herpesvirus 1 in vero cells, when the vero cells would not take infection at all, beyond passage numbers 130 or so. 
The issue is, the cells grow well at the high passage numbers, but do not seem to get infected much. 
These were the experiences with culture-adapted viruses; and I was wondering whether it would be the same situation if I use a highly passaged cell line for virus isolation from clinical specimens. (Say, for arboviruses, rotaviruses etc.)

It may also depend on the rate at which you are trying to infect them (eg multiplicity of infection). When the cells are at a lower passage and perhaps growing slower, it will be easier for the virus to infect. Perhaps at a higher passage the cells are growing so well that they overwhelm the virus in your samples. I would try infecting the cells at various levels of confluence to see if that helps. Our assays involve infecting cells at an optimal cell seeding level, and this can vary between viruses even when using the same cell line.