Melanie B. Megginson, MPH¹, David Blythe, MD, MPH², and Patricia A. Ryan, MSc¹. (1) Emerging Infections Program, Maryland Department of Health and Mental Hygiene, 201 West Preston St., Baltimore, MD 21201, 410-767-6261, mmegginson@dhmh.state.md.us, (2) Epidemiology and Disease Control Program, Maryland Department of Health and Mental Hygiene, 201 West Preston Street, Baltimore, MD 21201

Background: Listeria monocytogenes (LM) can cause severe and sometimes fatal illness in humans. Historically, difficulty has occurred in recognizing common source outbreaks of LM quickly because of variable and often lengthy incubation periods, numerous contamination vehicles, and the lag time involved in molecular typing.

Methods: The Centers for Disease Control and Prevention and the Council of State and Territorial Epidemiologists collaborated to develop a standard Listeria case report form. The Maryland Department of Health and Mental Hygiene (DHMH) used this form to investigate a temporal cluster of LM in the fall of 2003.

Results: DHMH identified 8 laboratory confirmed cases of LM among Maryland residents with onset dates from 9/18/2003 to 10/03/2003, compared to the previous 5-year baseline average of approximately 19 cases/year. The case report form was used to collect demographic information and food consumption histories. Case report forms were completed for 7 of 8 cases prior to the availability of final Pulse Field Gel Electrophoresis (PFGE) molecular typing results. Four cases (50%) were male. Median age was 63 years (range 1 day – 80 years). Two deaths occurred. Cases were clustered in the Washington and Baltimore Metropolitan Areas. Food histories revealed no specific food items in common. PFGE was performed on all cluster isolates. Only 2 of 8 isolates matched; however no common food item linked these two cases.

Conclusions: While these cases were temporally and geographically clustered, the data suggested this was not a common source food-related outbreak. This finding was only later confirmed by PFGE.

Learning Objectives: At the conclusion, participants in this session will be able to

• Describe a cluster of listeriosis in Maryland in the fall of 2003.
• Discuss the advantages and disadvantages of collecting lenghty food histories for sporadic cases of listeriosis.
• Identify reasons why case report form information can be available more quickly than molecular typing.

Keywords: Epidemiology, Infectious Diseases

Presenting author's disclosure statement:
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.