A Wal-Mart in Germantown, a northern suburb of Milwaukee was shut down around 1pm local time with 47 people hospitalized from a strange odor in the store. A substance has been found in the store. They are not ventilating the store, as they do not want to contaminate the outside air and the store is still closed at this hour. Here's several stories on the incident....
Just as an update to this story, another SuperCenter Wal-Mart in West Bend, 16 miles from the Germantown store was closed for around 2 hours after reports of a strange odor which was investigated. The store was re-opened around 8:15am.
As for the Germantown store, as of 11:30am local time today, is still closed. They are cleaning up the area where they found a "substance" as well as the rest of the store. They don't even know if the samples they took last night are the cause of the throat irritation and breathing problems. There is no time-frame as to when the store will re-open.
UPDATE: The store opened at 5:30pm local time last night. After extensive cleaning and re-stocking including throwing out all the produce. They still are not releasing what this substance was inside. First doctors were told they were working with ammonia poisoning, then that was changed later on. All 47 people are expected to be just fine.