Three elderly men have died and at least one pregnant woman has miscarried since last June after drinking listeria-contaminated pasteurized milk from Whittier Farms in Shrewsbury, Massachusetts. At least two others have been sickened as well. According to the Massachusetts Department of Health, tests have found no problems with the pasteurization process at the Whittier Farms plant, so investigators have turned their attention to the cooling and bottling machinery. So, the question really becomes where in the process did the milk become contaminated? Assuming that it really was not a problem in under-pasteurization, where, after heating, was the listeria bacteria introduced?

The families of victims of this outbreak have recently contacted us. One of the questions asked is how listeria survived pasteurization or how it was contaminated after pasteurization. Historically, there have been bacteria outbreaks tied to pasteurized milk, but the outbreaks seem tied to under-pasteurization or post-pasteurization contamination.

Date – Location – Species – Cases

1966 – Florida – Shigella flexneri – 97

1975 – Louisiana – Salmonella Newport – 49

1976 – New York – Y. enterocolitica – 38

1978 – Arizona – S. Typhimurium – 23

1979 – UK – Campylobacter jejuni – 3,500

1982 – Tenn., Ark., Miss. – Y. enterocolitica – 172

1983 – Massachusetts – Listeria monocytogenes – 49

1984 – Kentucky – S. Typhimurium – 16

1985 – Illinois – S. Typhimurium – >150,000

1986 – Vermont – Campylobacter jejuni – 35

1992 – UK – Campylobacter jejuni – 23

1992 – UK – Campylobacter sp. – 110

1994 – Illinois – L. monocytogenes – 45

1995 – UK – Campylobacter sp. – 12

1995 – Vermont, New Hampshire – Y. enterocolitica – 10

1999 – UK – E. coli O157:H7 – 114

2000 – Pennsylvania, New Jersey – S. Typhimurium – 93

2004 – Denmark – E. coli O157:H7 – 25

2005 – Colorado – Campylobacter jejuni – 40

2006 – California – Campylobacter jejuni – 1,644

Listeria monocytogenes (Listeria) is a foodborne disease-causing bacteria; the disease is called listeriosis. Listeria can invade the body through a normal and intact gastrointestinal tract. Once in the body, Listeria can travel through the blood stream but the bacteria are often found inside cells. Listeria also produces toxins that damage cells. Listeria invades and grows best in the central nervous system among immune compromised persons, causing meningitis and/or encephalitis (brain infection). In pregnant women, the fetus can become infected, leading to spontaneous abortion, stillbirths, or sepsis (blood infection) in infancy.