Report: Multistate Salmonella outbreak linked to hummus, tahini

December 3, 2012

Sesame seed paste containing a rare strain of Salmonella sickened 23 people in 7 states and the District of Columbia in 2011, reveals a new report from the U.S. Centers for Disease Control and Prevention (CDC). The report summarizes the investigation led by the District of Columbia Dept. of Health.

On Sept. 27, 2011, three clinical isolates of Salmonella enterica serotype Bovismorbificans with indistinguishable pulsed-field gel electrophoresis (PFGE) patterns were identified by the Washington, D.C. Public Health Laboratory (PHL). Through query of PulseNet, the national molecular subtyping network for foodborne disease surveillance, six additional cases were identified in three states (Maryland, Michigan, and Virginia) during the prior 60 days. All nine patients had eaten at restaurants in D.C. or northern Virginia less than 2 weeks before illness onset.

PulseNet was used throughout the investigation to monitor the outbreak PFGE pattern. Cases were defined as laboratory-confirmed Salmonella Bovismorbificans infection with the PFGE pattern of the outbreak strain in a person anywhere in the United States with illness onset during August 2011–Jan. 23, 2012. State and local health departments, the CDC, and the Food and Drug Administration (FDA) collaboratively investigated the outbreak. A total of 23 culture-confirmed cases with PFGE patterns indistinguishable from the outbreak strain were identified. Illness onsets occurred during August 19–Nov. 21, 2011, and peaked during Sept. 8–Oct. 12. The majority of cases were identified in the mid-Atlantic region of the United States: D.C. (eight), Maryland (seven), and Virginia (three). One case per state was identified in California, Delaware, Michigan, New Hampshire, and New Jersey. All 23 patients received outpatient medical care. No hospitalizations or deaths were reported.

On May 30, 2012, traceback indicated that contaminated tahini (sesame seed paste) used in hummus prepared at a Mediterranean-style restaurant in D.C. was a plausible source of Salmonella infections. The D.C. Dept. of Health restricted the sale of hummus and prohibited the use of hummus ingredients in other food items at implicated restaurants to prevent further illness. The traceback revealed tahini used at the different restaurants in the D.C. metropolitan area came from a common foreign manufacturer from Lebanon associated with recent Salmonella outbreaks in Canada. The FDA issued a mandate that all products imported from this manufacturer undergo Salmonella testing before entry into the United States. At the time of this report, the FDA recommended coordination with Canadian officials to conduct a foreign inspection of the tahini manufacturing plant.

This is the first report of Salmonella Bovismorbificans associated with tahini in the United States. Sesame seeds used to make tahini are high in fats, similar to peanuts. Salmonella species can survive for long periods in high fat foods (e.g., peanut butter), and if seeds or nuts are improperly processed (e.g., roasted at inadequate temperatures). Recalls of tahini for possible Salmonella contamination have occurred in the United States, but an outbreak as a result of tahini consumption has never been reported.