"Experts say such attacks are extremely rare—and instances where more than one person is attacked are even more rare.
'You are more likely to killed by a bolt of lightening than by a dog,' said Adam Goldfarb, a spokesman for the Humane Society of the United States. 'It's one in millions.'"
And the statistics actually back those statements up.
"In the United States, there are an estimated 25 million lightning flashes each year. During the past 30 years, lightning killed an average of 58 people per year. This is higher than 57 deaths per year caused by tornadoes and average 48 deaths to hurricanes. Yet because lightning usually claims only one or two victims at a time and does not cause mass destruction of property, it is underrated as a risk. While documented lightning injuries in the United States average about 300 per year, undocumented injuries are likely much higher." -- National Weather Service
Compared to;
"There have been at least 20 deadly dog attacks in the U.S. this year, 22 in 2008 and 33 in 2007, Goldfarb said, compared with about 75 million owned dogs. Many dogs that turn vicious aren't necessarily pets but kept for hunting or breeding, or as guard dogs." - The article in the link.