Environmental Engineering Reference
In-Depth Information
cases, resulting in at least two deaths and probably 12 related deaths. It was
estimated that 183,000 or more persons were infected. The outbreak had been
preceded by at least three smaller outbreaks. Evidence pointed to milk blending
via a cross-connection between a pasteurized milk transfer line and a raw milk
line. Other causes such as suction in a milk line that could draw raw milk past
two valves could not be ruled out. The cross-connection was an in-plant modi-
fication. Outbreaks such as this emphasize the complexity of modern processing
equipment, the importance of plan approval, the continual necessity for evaluation
of plant piping systems and controls, education and training of personnel, and
constant supervision and surveillance. According to a class-action suit reported
in the Baltimore Sun , the milk company must offer 2,100 people who “represent
about 15 percent of all those involved in the lawsuit ... up to $1000 plus medical
and employment compensation.” 51
Despite the ban on interstate sales of raw milk implemented in 1987, raw
milk has continued to cause numberous outbreaks. In 1995, 54 percent of states
permitted the intrastate sale of raw milk, although the estimated volume of raw
milk in states where sales was legal was less than 1 percent of the total milk
sold 48 . Of 46 raw-milk-associated outbreaks occurring from 1973 to 1992, 87
percent occurred in states where sales of raw milk were still legal at the time of
the outbreak. 48
Contamination of pasteurized milk has also been involved in several outbreaks,
likely due to contamination of milk products after pasteurization. At least 12
outbreaks occurred in the United States during 1960 to 2000 associated with the
consumption of pasteurized milk, including Salmonella typhimurium outbreaks
in Arizona in 1978 97 and Pennsylvania in 2000. 52 One of the first outbreaks of
yersiniosis associated with milk was reported in 1976, and was caused by milk to
which chocolate syrup had been added after pasteurization. A Yersinia outbreak
linked to postpasteurization contaminated milk affected 17,000 persons in Mem-
phis in 1982. 53 Salmonellosis has also been associated with the consumption of
nonfat powdered milk. 54
In addition to outbreaks caused by raw milk, soft cheeses made from raw milk
have been associated with Listeria monocytogenes infection. 55 Listeria grows
at below refrigeration temperatures, making it hazardous in raw milk products
(cheeses), unpasteurized milk, and pasteurized products that have been contam-
inated after pasteurization. A large outbreak, which included 142 cases with
48 deaths, occurred in California in 1985 and was linked to consumption of a
Mexican-style cheese made with raw milk. 56 Victims filed damage claims for
$100 million. The manufacturer of the cheese went out of business. A jury
found the manufacturer responsible, but the supplier of raw milk was exon-
erated. The federal investigators could not determine whether the raw milk,
improper pasteurization, or postpasteurization contamination was the cause. 57
Listeria monocytogenes has also been found in seafood and turkey franks. Other
outbreaks have been reported in Canada, Massachusetts, Los Angeles, California,
and Switzerland.
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