According to the DC Department of Health, the Food Safety & Hygiene Inspection Services Division (FSHISD) shut down the Wendy's at 3900 Georgia Avenue NW on Thursday, March 17th for a health violation. Not a happy St. Patty's Day for Wendy.
According to information from the Dept of Health, Wendy's was closed due to "Failing to minimize the presence of insects, rodents and other pests on the premises." The official report will probably be posted on the DoH website in the next week or two.
No word on when Wendy's may reopen, but it could be as early as tomorrow depending on the specific reason for the closure and what the restaurant needs to do for remediation and gets permission from DoH to reopen. There were employees working in the store on Thursday evening after it was shutdown.
Update 3/20: I believe the store reopened the next day.
Side note, I met Dave Thomas, owner of Wendy's, when I was in college. He was an awesome guy, dedicated to working with orphans (he himself was an orphan). He was a very kind fellow to put up with a college student. He passed away in 2002. Read more about Dave.
(h/t Tim Regan)