Some frogs have been alive, but the majority of frogs they are finding in the bags have been dead. In the last week, there have been over 1,700 consumer complaints filed on USA.gov.
There is no one particular brand to blame, although the majority of frogs have been found in products sold at Walmart.
One theory of why there has been an increase of frogs in the vegetation sold in grocery stores, is due to the droughts. It seems the frogs are migrating to areas where there is moisture, then hiding within the lettuce leafs.
It is a big concern for consumers, considering frogs frequently carry the germ salmonella that can cause serious illnesses in people. The CDC suggests that you inspect your vegetation thoroughly before you eat it.
If you find a contaminated bag, do not attempt to wash the vegetables! You cannot simply wash away salmonella.
Return it to the store, or simply throw it away.