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By Carol Christian | November 12, 2013 | Updated: November 12, 2013 4:31pm

Half-dollar size tar balls found washed ashore, Monday, May 20, 2013, at Bermuda Beach. Small, thick, wet oil masses were also visible in the seaweed over a roughly 2.5-mile span. (AP Photo/The Galveston County Daily News, Chris Paschenko)

The number of people contracting the warm-water bacteria that can cause illnesses ranging from tummy upsets to potentially fatal skin lesions has increased in recent years, according to federal data. Records kept by the U.S. Centers for Disease Control and Prevention show that the number of cases of Vibriosis nearly doubled between 2008 and 2012 – rising from 588 to 1,111. Vibriosis includes “Vibrio vulnificus,” the bacteria commonly dubbed “flesh-eating.” It’s rare but tends to be underreported, the CDC says on its website.

The CDC data on vibriosis includes all vibrio species except cholera, so it’s unclear how much of the increase in the past five years is due to infection by the flesh-eating bacteria that can cause death. One researcher who studies Vibrio vulnificus found it highly concentrated in tar balls that appeared along the Gulf Coast after the 2010 BP Deepwater Horizon oil spill. Covadonga Arias, a professor of microbial genomics at Auburn University in Alabama, found that Vibrio vulnificus was 10 times higher in tar balls than in sand and up to 10 times higher than in seawater.

Her research, conducted with colleagues Zhen Tao and Stephen Bullard, was published Nov. 23, 2011, in EcoHealth. It marked the first analysis of bacteria found on the large amounts of “weathered oil” (such as tar balls) from the BP Deepwater Horizon spill that ended up on the shoreline, the researchers said. For the study, samples of sand, seawater and tar balls were collected from July through October, 2010, from a beach in Alabama and two beaches in Mississippi. The authors said their findings have epidemological relevance since many people have stepped on tar balls or picked them up on the beach.

However, in a June 2012 letter to BP, Dr. Thomas Miller, the deputy director for medical affairs at the Alabama Department of Public Health stated, “There is no epidemiological evidence to indicate increased rates of Vv (Vibriosis vulnificus) infections. Analysis of current and previous years’ Vv case numbers indicates there is no increase in the number of cases for years 2010 – 2012.”

BP spokesman Jason Ryan said in an emailed statement: “The Auburn study does not support a conclusion that tar balls may represent a new or important route of human exposure for Vibrio infection, or that the detection of Vibrio in tar balls would impact the overall public health risk, since there are other far more common sources of Vibrio, such as seawater and oysters.
“This is a naturally occurring bacteria found in the Gulf of Mexico. Neither the Alabama Department of Health nor the Centers for Disease Control have reported any significant increase in cases in the last three years and no individual case of vibrio infection has been linked to tar ball exposure.”

While there is no proof that tar balls can infect humans, Arias said it’s a concern because the bacteria concentration is so high in the samples her team studied. “At a concentration as high as 1 million Vibrio vulnificus cells/g (per gram) of tar ball, I think the potential risk is there,” she said by email. Concentrations in oysters and seawater are typically much lower, she said. To prove that tar balls can infect humans will require more study, which takes a lot of money, she said.