A wide variety of bacteria can cause the disease. The most common is group A streptococcus, the same germs responsible for strep throat. This is the only type of necrotizing fasciitis that is formally tracked, and 700 to 1,100 cases are recorded in the United States each year, according to the Centers for Disease Control and Prevention. Other culprits include E. coli, Staphylococcus aureus, Aeromonas hydrophila, and members of the Clostridium and Klebsiella genera.

When The New York Times organized testing in Houston after the hurricane, floodwaters in two neighborhoods showed extremely high levels of E. coli: in one home, 135 times the level considered safe.

The sample in that home also tested positive for Vibrio bacteria. It was not possible to identify the specific strain, but one — Vibrio vulnificus — is known to cause necrotizing fasciitis, said Charlotte Smith, an environmental health expert at the University of California, Berkeley’s School of Public Health who helped The Times analyze the data.

Dr. Smith said she was not surprised that necrotizing fasciitis infections had occurred. Cases were also recorded after Hurricane Katrina, she noted, because of the confluence of two factors.

“One is the breakdown of the infrastructure as a whole, which brings more microbes into the environment,” Dr. Smith said. “The second is the conditions of people that are in that environment: They have high potential for cuts and scrapes that would make one more susceptible.”

Activities like taking furniture to the curb or removing drywall can easily cause the cuts and abrasions that allow bacteria in.