SYMPOSIUM
linked to raw oyster consumption, and about half of these case-patients die. When a case of V. vulnificus in- fection or similarly serious seafood- related illness is reported, the Sea- food Safety section investigates the establishment. Raw oysters, because of their risk for being the source of potentially serious food-borne illness, must, by law, bear tags indicating ex- actly when, where, and by whom they were harvested. These tags must be retained by the eating establishment for at least 90 days. This tag require- ment makes it possible to trace raw oysters consumed by an ill person back to the oysters’ source. Most con- taminated food items cannot be traced so readily.
MYSTERY SOLVED
The Seafood Safety director worked with the regional and local health de- partments with jurisdiction where the case-patients lived. The health depart- ment staff members contacted the res- taurants where the case-patients had reported eating and obtained copies of the oyster tags potentially relevant for the patients’ illnesses. (Because oys- ters can be sold for up to two weeks after harvest, and a restaurant might obtain raw oysters from several differ- ent sources, it isn’t always clear which oysters might have caused a patient’s illness.) The Seafood Safety direc- tor compiled the information into a spreadsheet and sent it to the de- partment’s epidemiologist. The table showed the answer they had all been looking for: All six case-patients had consumed raw oysters on at least one occasion that were harvested from the same area of the Gulf of Mexico, by the same raw oyster dealer, by the same boat and the same crew. The im- plicated oysters were harvested over a 12-day period. The mystery had been solved using advanced scientific de- tective skills and dogged perseverance. It remained to be determined if any
of the implicated oysters were still in commerce. By the time the mystery had been solved, at least two months
had passed since the oysters had been harvested. The TDH Seafood Safety director worked with the oyster dealer to determine where oysters harvested from the specific area of the Gulf dur- ing the period of harvest for the out- break case-patients had been shipped. All of these establishments were contacted, and none had any prod- uct remaining from that time period. It turned out that a different nearby dealer had purchased some oysters from the implicated dealer because he couldn’t harvest enough oysters to meet his customers’ demand. This second dealer sold only raw
oysters he treated using an approved post-harvest treatment process dem- onstrated to reduce V. vulnificus bac- teria to below-detectable levels. The process involved flash freezing and holding below freezing for a period of time. What this dealer didn’t know was that bacteria are not readily killed by freezing temperatures. In fact, all strains of Salmonella are quite hardy. The Seafood Safety director collected 30 samples of the implicated oys- ters, which had been comingled with other oysters, but none were found to contain S. Typhi. All workers still employed with the dealer provided clinical specimens for testing, but none grew S. Typhi. The director also required that the dealer destroy all remaining implicated product he pos- sessed. The source of the oyster contami- nation that caused the outbreak could not be identified. It could have oc- curred at the harvest site, which was near the Houston ship channel where many ships pass and one might have (illegally) discharged S. Typhi-con- taminated sewage. Or a worker on the harvesting boat might have dumped urine or sewage over the side of the boat. It most likely occurred while the oysters were still in the bay waters, as during and after harvest the oysters’ shells would remain closed until pried open for consumption. The best news was that no additional cases had been detected.
PROVIDING PROTECTION
This is an especially dramatic example of the protection that the high-tech, highly trained, and dedicated mem- bers of the public health community provide to Texans every day. We hope that the physician and
health care professional community will take special note of the fact that, in each case, this serious and poten- tially fatal communicable infectious disease only came to the attention of the public health response team because of the knowledge, skill, and diligence of the professionals involved. The treating physicians had to have an index of clinical suspicion sufficient to order testing, and the laboratories had to have the skill to identify the culprit and take the steps required to report their finding. Only then could public health take action to identify and rem- edy the source. The teamwork of professional acu- men, laboratory expertise, and public health investigation is the basis for all of our efforts to protect the public. Re- member: The public is all of us.
Linda Gaul, PhD, is the state epidemi- ologist. She was a faculty member in biological sciences at The University of Texas at Austin for 11 years.
John Hellerstedt, MD, is commission- er of the Texas Department of State Health Services. Before that he served as chief medical officer of the Seton Family of Hospitals.
February 2017 TEXAS MEDICINE 41
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