As of the time of this writing, Google does not provide a USB driver (for Windows) for the Nexus 5. The usual link (http://developer.android.com/sdk/win-usb.html) shows Wind
After trying the other solutions I was able to send ADB commands to the phone as long as it was booted into Android. However, when the phone was in recovery mode I encountered a new problem, and I would like to contribute my experience here.
While booted into Android the phone installed in Windows as a device named "Nexus 5". After the phone was powered down and booted into recovery mode, the phone was still installed as "Nexus 5", but ADB could not detect the device. I had to manually force the driver from "Nexus 5" to the Google USB driver provided with the SDK or available from Google USB Driver.
The .inf file has three devices available. I used "Android Composite ADB Interface" and everything seems to be working.