In the "Issue 60058: mmqcamera-daemon cpu usage", the person from Google posted that they have fixes for Nexus 5 current high CPU usage reports, due to the so called 'mm-qcamera-daemon' and that the fixes will be in the next maintenance update.
However, there was no specific date for that next maintenance update due to the tests that they have to do for the fixes. Until then, the only solution for the high CPU usage is rebooting the phone.
The IBTimes report that Android 4.4.2 Kitkat causes the battery drain issue. A software process in the OS allow apps to have camera access, and the mm-qcamera-daemon does not stop running even if the camera app has been closed. The camera uselessly running in the background leads to faster battery drain and persistent high CPU usage.
Another forum member complained he had the same experience, stating that a camera running in the background could use up to 50 percent of the battery, like most other smartphones. However, his Nexus 5 goes down up to one percent every two minutes and stands by while the camera is running. He observes that this did not happen with his previous Nexus running Android 4.4. He has had his Nexus 5 since November 17, 2013.
The Google project member admits they have received reports regarding the battery issue of Nexus 5 quite frequently, and claims it might have been related to the latest Skype update, which allows continuous access to the camera in the background and triggers a bug. Uninstalling Skype may give a temporary solution to the issue, though other applications that uses camera can also trigger the bug.
The camera issue has been affecting Qualcomm-powered and Kitkat-based devices. Google has a reputation of sending issue fixes quite fast. In December, some Nexus owners sent back their devices to the company due to certain issues including noisy buttons, protruding SIM-tray, and a cutting-edge screen frame. Google later rolled out new batch of Nexus 5 with more flush buttons to prevent noise, and the SIM-trays were fixed.