Researchers have discovered the first U.S. cases of whooping cough caused by a germ that may be resistant to the vaccine.
Health officials are looking into whether cases like the dozen found in Philadelphia might be one reason the nation just had its worst year for whooping cough in six decades. The new bug was previously reported in Japan, France and Finland.
"It's quite intriguing. It's the first time we've seen this here," said Dr. Tom Clark of the Centers for Disease Control and Prevention.
The U.S. cases are detailed in a brief report from the CDC and other researchers in Thursday's New England Journal of Medicine...
