The state lab that tests the blood of suspected intoxicated drivers for drugs is facing a backlog of nearly 1,000 samples – and mounting – that threatens public safety, prosecutors and lab officials say. Delays at the Wisconsin State Laboratory of Hygiene mean both innocent drivers and serial offenders at risk of harming other motorists are waiting several months longer than needed to receive justice. The hygiene lab, which is part of UW-Madison, does a variety of tests, from testing for swine flu to screenings of newborns for genetic diseases. The drug testing delays at the hygiene lab are similar to a DNA testing backlog at the state Crime Laboratory that drew headlines in recent years.