January 21, 2018

Social Media Aids Las Vegas Marathon Sapovirus Outbreak Investigation

On December 4, 2011, the annual Rock ‘n Roll Las Vegas Marathon took place. More than 40,000 runners attended. Two days later, there were reports of illness to the Southern Nevada Health District (SNHD). And the event’s Facebook page started accumulating complaints of illness.

Food Poisoning Bulletin has reported before about the use of social media in outbreaks, how experts want to use these tools to track outbreaks, and how the government uses Twitter to keep people informed about recalls and outbreaks.

The water distributed at the race itself didn’t seem to be the source of the outbreak, despite many people focusing on that as the cause. The water was pumped from hydrants along the race course and stored in plastic-lined garbage cans.

Some runners reported that volunteers were dunking cups into the water with ungloved hands, and seeing some runners disposing used cups in the water containers. Both of these actions can spread illness. These are some Facebook comments from race participants.

“Such a bummer that this was my first half marathon 🙁 I’ve been sick with stomach problems for 8 days now,have lost considerable weight,and haven’t gotten to work out.”

“Day after race I had pain in my urinary track. Went to ER 2nd day with bacteria found. Now pain in stomach. Initial diagnosis is prostatitus (sp?). Said from infection caused by bacteria in stool. Coincidence? I have been on antibiotics since race and given month’s worth. CT scan next week to rule out kidney stones. Anyone with similar issues. I did drink the garbage can water.”

“I got sick at mile 12. Stomach cramps. Afterward i was stuck in the finishing area, on the verge of a panic attack because I began to feel claustrophobic. I shivered with chills for an hour AFTER I was in my heated car.”

Solving the Case

The SNHD just released a final report on the outbreak. The SNHD states they used Facebook and Twitter to investigate.

To try to solve this case, the Southern Nevada Health District posted an online survey to question those who were ill. Of the 1,082 people who completed the survey, 528 met the case definition, with reported symptoms of foodborne illness, including vomiting, cramps, and diarrhea.

The interim report did not identify the cause of the illness, except to say that diarrhea typically takes at least 12 hours to develop after infection. Since many runners reported symptoms while running the marathon, the “garbage can water” could not have been to blame.

Nine people submitted stool samples; two tested positive for sapovirus. The samples were cultured for Salmonella, Shigella, Campylobacter, E. coli 0157:H7, Yersinia, STEC E. coli, Cryptosporidium, and Norovirus.

The survey was shared on the marathon’s Facebook page, which had more than 25,000 followers at the time. And 22 people shared the link on Twitter, reaching almost 18,000 followers.

Most of the respondents, 85%, reported having diarrhea. Vomiting was reported by 56%, and fever by 31%. Most people became ill between 6 pm and midnight on December 4, 2011.

Investigation Results

The investigation points to exposure at the health and fitness expo that took place before the race as the most likely source of the sapovirus outbreak. That event fits into the exposure time frame.

A sports drink was handed out at the race; it was made from the same water handed out to runners. But the incubation time of the illness ruled out the drink as the source of the outbreak.

Sapovirus is similar to norovirus with a short incubation time and low infectious dose. This was the first outbreak of sapovirus in Southern Nevada, and the first time it has been identified in the local population.

The SNHD wasn’t able to conduct an on-site environmental investigation, since the race site was cleaned up before the investigation was launched. The race setup wasn’t investigated by the health department, since athletic events don’t need a permit.

Vendors at the expo were not required to obtain a permit to hand out samples, so no information about potential risks at the vendor booths was available. Investigators couldn’t pinpoint the source of the outbreak for this reason.

And since lab samples weren’t collected until week after illness onset, some people probably had sapovirus but had finished shedding it by the sampling time.

Another complication into the investigation was the fact that distance runners often exhibit symptoms of gastrointestinal illness after a run because of the stress placed on their bodies.

Looking Ahead

The SNHD said, “Using the active community of runners on Facebook and Twitter allowed for the rapid dissemination of the survey directly to the exposed population without a delay in requesting participant information from the race organizers. Comments posted to social media sites provided ongoing, real-time insight into the needs and concerns of the ill population, and provided a feel for the efficacy of health district investigation efforts.”

The SNHD recommends that large event planners may want to set up social media sites for that event, after careful planning. And the department has started thinking about developing regulations for oversight and monitoring large scale public events.

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