Actually, there is likely no way to know either how many virus attacks were intercepted by anti-virus software. Or, how many of these attacks were reported. There are just too many sources to attempt to compile the data. Many sources like companies often do not share their infection rates.
You can get a clue as to which viruses are the most prevalent by looking at the list of viri that the Microsoft Malicious Software Removal tool looks for and removes.
Still, any report is going to be very incomplete. Many users turn off the reporting function so the AV providers do not get data from those systems. And, most corporate IT departments do not share attack rates with anyone outside of the company.
Mid September a sudden rush on a day or two, these match a report from Symantec on an increase in generic polymorphic malware variants which went from 18.5 percent to 72.0 percent of email borne malware for the month (http://www.symanteccloud.com/en/au/globalthreats/charts/virus_monthly)
End of the month a sudden surge in the amount of SPAM being dropped by reputations, along with an increase of mail getting delivered, suggesting that more SPAM was getting through our first line which is based on SPF, reputation, RAV, etc but no where near the levels from 8 months ago, let alone this time last year.
Besides those spikes another average month, mind you with the corleation between SPAM and email malware, and increase in one normaly means and increase in the other.