As Australia reviews its ban on raw milk cheese – with the usual arguments about good and bad bacteria and artisinal crafsmanship  — the Institute of Health in France reports that on Oct 1, 2012, six human cases of Lm infection with the AscI/ApaI PFGE pattern 210792-210792 over the previous 6 weeks were identified by the National reference center for Listeria. PFGE-typing using restriction enzyme SmaI identified 2 distinct profiles, D and Q.

On Oct 22, additional PFGE-matching cases were identified. An outbreak investigation was initiated to identify the source of contamination and guide public health actions. We defined a case as a Lm infection with a PCR-genoserogroup IVb and the PFGE AscI/ApaI 210792-210792 profile diagnosed in France between Aug 1, 2012 and Feb 11, 2013. SmaI Q-associated cases were considered epidemic whereas SmaI non-Q-associated cases were considered non-epidemic. Cases’ food consumption history was collected using a standard questionnaire. We conducted a case-case study, aiming at comparing the food consumption history of both epidemic and sporadic listeriosis cases identified during the same period, as well as traceback and traceforward investigations.

The implicated cheese factory was inspected. Food and environmental samples were collected.

Twenty-five cases were identified (11 epidemic cases). Dates of diagnosis ranged from Sep 4, 2012 to Nov 20, 2012. Consumption of raw milk brie cheese was significantly associated with the outbreak SmaI Q strain (Odds Ratio 35, IC_95% [5-366]). Traceback and traceforward investigations identified Cheesemaker. A as the likely source of infection. Cheesemaker inspection did not identify any hygiene violation. Food and environmental samples did not yield the outbreak strain. A point-source contamination of the raw milk is suspected to have occurred.

(Thanks to Albert Amgar for forwarding the document.)