In December, Zhi-Qiang Deng and his research team predicted the Cameron Parish oyster norovirus outbreaks 16 days before they occurred.
“This is the first time in the world that scientists have been able to predict a norovirus outbreak in advance,” Deng said.
Deng’s model — still in its preliminary stages — relies on science and mathematical probability to determine the likelihood that a norovirus is present in a particular Louisiana oyster harvest area.
And, thus, it has the potential to prevent such outbreaks in the population from occurring at all.
Symptoms of noroviruses usually begin 12 to 48 hours after consuming a diseased oyster and can include nausea, vomiting, diarrhea and stomach cramping, according to the state Department of Health and Hospitals. Sometimes people also experience low-grade fevers, chills, headaches, muscle aches and fatigue.
Cooking kills the virus. The illness usually is brief, with symptoms lasting one or two days.
Louisiana is the top producer of oysters in the nation, with around 1.3 million Louisiana oysters being consumed somewhere in the United States, DHH statistics show.
Mike Voisin, owner of Motivatit Seafoods in Houma and a member of the Governor’s Oyster Advisory Committee, says “anything that can be done to improve the predictability (of outbreaks) would be supported by the oyster community, because the last thing we want is for someone to have a problem after they consume our product.”
Not having yet heard of the model, though, Voisin also fears that misuse of such a predictor could lead to the unnecessary closure of oyster areas that would not have made anyone ill.
On Dec. 28, the Louisiana Department of Health and Hospital closed an oyster harvesting area in Cameron Parish after nine people became sick to their stomach after eating oysters harvested from that area. DHH also issued a recall for all oysters from that specific basin and harvest area, including shucked, frozen, breaded, post-harvest processed and oysters for the half shell market.
On Dec. 12, Deng’s model had correctly predicted that very norovirus outbreak.
The nine people who became sick were not hospitalized and their illnesses were not life threatening.
Deng met in January with DHH officials including Dr. Jimmy Guidry, the state health officer, to present his preliminary results.
“He has definitely piqued our interest,” Guidry said. “Next steps for us would be to get some other subject experts together to review his study.”
Basically, the model predicts future water quality conditions and bacteria levels by using water temperature, tidal levels, salinity, rainfall and state sampling data. Most of those variables are tallied from temperature and tidal gauges, but Deng also uses NASA imagery from the Terra and Aqua satellites. Colors from those satellites’ images can be converted to temperature using various algorithms.
The project is funded through a $225,000 NASA grant.
The DHH’s Molluscan Shellfish Program currently regulates state oyster harvesting areas. It has eight staff members, divided into four crews, who test all the oyster grounds in the state at least once a month, taking 10 to 15 samples in each oyster bed, Guidry said.
But the state hardly ever closes the grounds due to such sampling. And so other than during major environmental events such as hurricanes or oil spills, the process usually is retroactive. People get sick and report the illness and then a recall of area oysters is issued, and the oyster ground culprit is shut down, typically for about 21 days.
Also, DHH only is testing for elevated fecal coliform levels.
Those are used as a measure of contamination by bacteria and viruses found in the human gut. However, Deng points out, fecal coliform levels often are elevated in the summer but oysters hardly ever get the virus then.
That’s because cold water is one of the other factors needed for the disease to develop.
Deng has determined that a norovirus typically occurs when a variety of conditions occur. It normally occurs in oyster grounds about 10 to 14 days after an extremely low tide.
The grounds also need extremely low water temperatures and high bacteria levels for the virus to develop. And heavy rainfall after a long dry period typically transports bacteria from land to an oyster growing area, Deng says.
So, one factor alone often will not cause the virus. The model’s predictions are based on them all.
In addition to the predication model, Deng is partnering with Southern University of New Orleans scientists who will use the model and its data to develop a website showing real-time bacterial levels and norovirus predictions in oyster growing areas.
Deng also said he possibly can tweak the model down the line to predict vibrio vulnificus illness, a rare but deadly bacteria sometimes present in raw oysters, and red tide, which also can be deadly.
Voisin said that while shutting an oyster ground hurts business, the recalls and subsequent negative publicity are worse for harvesters’ pocketbooks. So, if contaminated oysters never go out into the market in the first place, it would be a win-win for oyster harvests and consumers.
“Some of the larger recalls have been in the millions of dollars,” Voisin said. “But if the model is obsessive, then you would not be able to harvest the resource because you are over-conservative.”
“What we need is the right mix, so we get to zero illnesses and still have a harvestable resource.”