Vibrio bacteria, an infection that is often mild but can turn lethal, may be a bigger threat this summer than usual. Experts report the bacteria that causes the infection are showing up in unusual places.  The infection is caused by about a dozen species of vibrio bacteria, the CDC says. One, Vibrio vulnificus, is common along the Southeastern U.S. coast. However, experts have found it has traveled farther north, to Delaware Bay, which has slightly cooler waters than the usual locations…