Maybe there wasn't anything in the water after all.
The Southern Nevada Health District still can't say what caused some runners to become ill during the Rock 'n' Roll Las Vegas marathon, but water served during the race does not appear to be the culprit, according to preliminary findings issued Thursday.
All the evidence collected so far points instead to a virus that runners were exposed to before the race, said Brian Labus, senior epidemiologist for the health district.
"For us, it looks like something infectious," Labus said. "We don't have any evidence that it was the water."
The findings are based on the answers runners gave in an online survey and on tests conducted of stool samples supplied by 11 people who got sick during and after the Dec. 4 race.
Labus said tests of the stool samples ruled out "the usual suspects" such as norovirus, salmonella and E-coli.
The samples have been sent to the Centers for Disease Control and Prevention for additional testing.
Over the past week and a half, Competitor Group, the San Diego-based company that owns and operates all the Rock 'n' Roll events, took the brunt of complaints about the water issue, particularly on Facebook and other social media outlets. The company released a statement after the health district's preliminary findings.
"Competitor Group has cooperated with the Southern Nevada Health District's investigation into the concerns of runners following the Las Vegas Marathon," the statement read. "We are pleased that Dr. Lawrence Sands, chief health officer, concluded, 'At this time, our investigation does not point to water given to runners as the likely source of the infection.' We will continue to support the health district in its ongoing efforts."
It's unclear how many runners were sickened, but dozens have posted their stories about falling ill on the event's Facebook page. Many have threatened to boycott future races organized by San Diego-based Competitor Group.
Some runners blamed the water, which was pumped from hydrants along the race course. Others pointed to the plastic-lined garbage cans where the water was stored and at event volunteers wearing plastic gloves who dipped cups into the garbage cans before passing the water to runners.
Of the almost 1,000 race participants who completed the health district's online survey, 531 reported illnesses. Roughly three-quarters of them said they fell ill during the race, with complaints that included vomiting, stomach cramps and diarrhea.
Labus said that last symptom strongly points to infection sometime before the race because diarrhea is not something that typically develops within minutes of exposure to a chemical, toxin or virus.
He added that runners who were given a sports energy drink during the race reported no elevated risk of illness, though the drink was made with the same water that was handed out along the course.
Las Vegas Valley Water District officials were not surprised by the findings.
They have said water from the fire hydrants was potable and tested clean days before the race. The health district's preliminary report bears that out.
"It was very unlikely that this was a water-borne illness," said J.C. Davis, spokesman for the water district.
Labus said the survey results also appear to rule out training and environmental factors because runners fell ill at about the same rate regardless of their experience level or their familiarity with running in dry, desert climates.
The investigation continues, he said.
"If it's not the water, it's got to be something else common to all these people," Labus said.
Review-Journal writers Lynnette Curtis and Patrick Everson contributed to this report. Contact reporter Henry Brean at firstname.lastname@example.org or 702-383-0350.