Fluctuation in contamination dynamics of L. monocytogenes in quargel (acid curd cheese) lots recalled during the multinational listeriosis outbreak 2009/2010

► Contamination level of L. monocytogenes in cheese lots that caused a multinational outbreak.. ► Challenge tests at 4, 15 and 22 °C were conducted; total number of analysed cheese samples 1045. ► Red smear type cheese lots were L. mono. positive (≤ log 8.1 CFU/g); white mold coated cheese negative. ► Smear process of red smear and mold coated quargel cheese took place in two different machines. ► Very probably contamination of cheese took place during the red smear process.