From early August 1998 through January 6, 1999, at least 50 illnesses caused by a rare strain of the bacterium Listeria monocytogenes, serotype 4b, have been reported to CDC by 11 states. Six adults have died and two pregnant women have had spontaneous abortions. Reported illness onset dates were during August 2-December 13, 1998. CDC and state and local health departments have identified the vehicle for transmission as hot dogs and possibly deli meats produced under many brand names by one manufacturer. This report updates the investigation of this outbreak.