SYMPOSIUM Typhoid fever on the half shell BY LINDA GAUL, PHD, AND JOHN HELLERSTEDT, MD
Protecting the public from communi- cable infectious disease outbreaks is one of the most important, and most challenging, functions of public health. Foodborne outbreaks are not uncom- mon, and they can be especially dif- ficult. This true story of the epidemio- logic investigation into a typhoid fever outbreak illustrates the critical impor- tance of timely reporting by front-line clinicians, extensive interprofessional teamwork, and statewide coordination.
THE FIRST CALL
This is a story of first-rate scientific detective work. It demonstrates the benefits that can flow from combin- ing advanced science with tenacious dedication and hard work. The first call came to the lead
foodborne illness epidemiologist at the Austin headquarters of the Texas Department of Health (TDH, now the Texas Department of State Health Services) one morning in late August 2003. The caller was an epidemiolo- gist at the City of Houston Depart- ment of Health and Human Services.
“I’m investigating a case of typhoid fever, and I’ve been talking with the epidemiologist in the Montgomery County Department of Health and Human Services [MCHHS], who is also investigating a case of typhoid fever. We’re wondering which of the Centers for Disease Control and Pre- vention [CDC] forms we should use to report these cases.”
The call piqued the interest of the TDH epidemiologist because of the unusual occurrence of two cases of typhoid fever occurring in the same area of the state during the same time period. Typhoid fever, caused by Sal- monella enterica serotype Typhi bacte- ria, is rare and not endemic within the
United States. About three dozen cas- es are reported annually in Texas, and nearly all are linked to travel outside the United States. However, the two new case-patients had not traveled outside the country during their incu- bation periods, which average 33 days but can be as long as three months. The more stunning news: The organ- isms from the two case-patients had the same molecular fingerprint. That meant the cases were most likely caused by a contaminated food. Now, it would be up to the epidemiologists to determine what that food was. The molecular fingerprint used in
this case was PFGE, or pulsed-field gel electrophoresis, a method of bacte- rial molecular subtyping. The treating physicians had ordered tests to deter- mine the cause of the illness. Once the culprit has been isolated and grown in the lab, a series of tests, including PFGE and molecular subtyping, can be performed. The subtyping results are uploaded to the PulseNet labora- tory network, an electronic database maintained by CDC. Once in PulseNet, public health epidemiologists around the country can compare the organisms recovered in their jurisdictions with those from other areas. The epidemiologists are notified when their isolates match (or very closely resemble) PFGE patterns found in other cases. This matching function allows outbreaks to be iden- tified that previously would have gone undetected because the cases were few in number or located far apart. For this outbreak, there were no simi- lar isolates outside of Texas. During the first round of informa- tion gathering, the two Houston-area adult male case-patients were inter- viewed at length, but no common food
or other exposure was identified. Both reported eating most meals in their own residences. These two cases were not the end. A few days later, the TDH epide-
miologist was notified of a third case, also in Harris County but within the jurisdiction of the Harris County De- partment of Public Health and Envi- ronmental Services. The specimen from this adult female grew out S. Typhi with the same PFGE pattern as the first two cases. This individual had also not traveled outside the United States before her illness onset. Further in-depth interviews did not reveal a likely common source for the three illnesses. The TDH epidemiologist knew
there had to be a common exposure because the PFGE patterns were not only highly similar but also rare. She hypothesized that the food vehicle was an unusual food item — prob- ably a food that is normally eaten without being cooked. She suggested the epidemiologists reinterview the case-patients using a more extensive 14-page questionnaire. The question- naire gathered names of places where the individuals had eaten and food items of specific concern, such as con- diments (e.g., banana peppers), as well as raw animal protein items, including raw oysters. (Raw, protein-containing foods of animal origin — oysters, raw milk, and steak tartare — are consid- ered delicacies by some.) The female case-patient had espe-
cially good recall for the foods she ate and the names of the establishments where she dined during the several months before her illness. She was thorough. She checked her credit card receipts and confirmed dates for the meals eaten away from home. She reported consuming raw oysters on two occasions at the same establish- ment in her area. Neither of the two male case-patients reported they had consumed raw oysters or eaten at the same food establishment. Neither man reported eating raw oysters during the several months before illness on-
February 2017 TEXAS MEDICINE 39
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