730 Modern Food Microbiology
cases in 1988, 7.3% were either foodborne or waterborne.
25 Among 88 elementary school students and
their teachers in 1990 in the state of Georgia, 15 came down with hepatitis A. Among 641 residents
and staff at an institution for the disabled in Montana, 13 contracted hepatitis A. Strawberry shortcake
was the vehicle in both outbreaks. The frozen strawberries came from the same processing plant in
California.
81
The largest foodborne outbreak of hepatitis A ever recorded in the United States occurred in November 2003, and there were ca. 600 victims with 3 deaths. The vehicle food was imported green onions
(scallions) served by a fast-food restaurant chain. Between 1992 and 2001, an estimated 230,000 cases
of hepatitis A were reported to the CDCP. In 2001, an outbreak of >46 cases occurred in Massachusetts
and it was associated with the consumption of sandwiches, which apparently were contaminated by a
food handler.
16
Noroviruses
The former Norwalk, Norwalk-like,and small-round-structured viruses (SRSV) have been placed
in this group as the genus Norovirus of the human caliciviruses (HuCV). The noroviruses are in two
genogroups, I and II. The former Norwalk group is the prototype for genogroup I, and the former
Snow Mounain viruses are in genogroup II. All of these viruses are unenveloped and ssRNA with a
diameter of 27–40 nm and their genome consists of 7,300 to 8,300 base pairs. The caliciviruses also
include the genus Sapovirus. For more information, see references 40, 86, 96.
The Norwalk virus was first recognized in a school outbreak in Norwalk, Ohio in 1968, and water
was suspected, but not proven, as the source. It is the most prevalent of the noroviruses in foods.
The virus is more resistant to destruction by chlorine than other enteric viruses. In volunteers, 3.75
ppm chlorine in drinking water failed to inactivate the virus, whereas poliovirus type 1 and human and simian rotaviruses were inactivated.
58 Some Norwalk viruses remained infective at residual chlorine levels of 5–6 ppm. Hepatitis A viruses are not as resistant as Norwalk, but both are
clearly more resistant to chlorine than the rotaviruses. The exposure of noroviruses to 0.37 mg/l of
ozone at pH 7 and 5
◦ C for up to 5 minutes in water effected a >3 log 10 reduction after a 10 second
exposure.
97
Of 430 foodborne outbreaks in the United States in 1979, 4% displayed the pattern of Norwalk
gastroenteritis.
57 This virus was thought to be the cause of more foodborne gastroenteritis than any
single bacterium in the state of Minnesota in 1985.
65 Noroviruses are now the leading cause of
gastroenteritis in the United States with an estimated 23 million cases per year.
17 From several cruise
ship outbreaks in 2002, there were at least 1,786 victims. Up to 21 ship outbreaks occurred during the
same general time period, and the virus appeared to come from unspecified environmental sources.
Of 1,412 outbreaks of foodborne intestinal diseases in England and Wales for the years 1992–1999,
82 (5.8%) were caused by noroviruses (all previously designated SRSVs). From the same survey, 12
of 60 (20%) were traced to fruits and vegetables.
96 Since they have yet to be cultured in the laboratory,
the method of choice is RT–PCR (see Chapter 11).
During the fall of 2001, a rare waterborne outbreak of norovirus gastroenteritis occurred in the state
of Wyoming, and there were around 84 victims. Ground water was contaminated with sewage, which
was the source of the human HuCV. The etiologic agents were identified by use of RT–PCR, which
demonstrated mainly genogroup I, subtype 3; but one stool sample yielded a genogroup II, subtype 6
strain.
86
Among the earliest reported outbreaks that involved noroviruses is one that occurred in 1976 in
England. Between December 21, 1976, and January 10, 1977, 33 outbreaks and 797 cases occurred,
cases in 1988, 7.3% were either foodborne or waterborne.
25 Among 88 elementary school students and
their teachers in 1990 in the state of Georgia, 15 came down with hepatitis A. Among 641 residents
and staff at an institution for the disabled in Montana, 13 contracted hepatitis A. Strawberry shortcake
was the vehicle in both outbreaks. The frozen strawberries came from the same processing plant in
California.
81
The largest foodborne outbreak of hepatitis A ever recorded in the United States occurred in November 2003, and there were ca. 600 victims with 3 deaths. The vehicle food was imported green onions
(scallions) served by a fast-food restaurant chain. Between 1992 and 2001, an estimated 230,000 cases
of hepatitis A were reported to the CDCP. In 2001, an outbreak of >46 cases occurred in Massachusetts
and it was associated with the consumption of sandwiches, which apparently were contaminated by a
food handler.
16
Noroviruses
The former Norwalk, Norwalk-like,and small-round-structured viruses (SRSV) have been placed
in this group as the genus Norovirus of the human caliciviruses (HuCV). The noroviruses are in two
genogroups, I and II. The former Norwalk group is the prototype for genogroup I, and the former
Snow Mounain viruses are in genogroup II. All of these viruses are unenveloped and ssRNA with a
diameter of 27–40 nm and their genome consists of 7,300 to 8,300 base pairs. The caliciviruses also
include the genus Sapovirus. For more information, see references 40, 86, 96.
The Norwalk virus was first recognized in a school outbreak in Norwalk, Ohio in 1968, and water
was suspected, but not proven, as the source. It is the most prevalent of the noroviruses in foods.
The virus is more resistant to destruction by chlorine than other enteric viruses. In volunteers, 3.75
ppm chlorine in drinking water failed to inactivate the virus, whereas poliovirus type 1 and human and simian rotaviruses were inactivated.
58 Some Norwalk viruses remained infective at residual chlorine levels of 5–6 ppm. Hepatitis A viruses are not as resistant as Norwalk, but both are
clearly more resistant to chlorine than the rotaviruses. The exposure of noroviruses to 0.37 mg/l of
ozone at pH 7 and 5
◦ C for up to 5 minutes in water effected a >3 log 10 reduction after a 10 second
exposure.
97
Of 430 foodborne outbreaks in the United States in 1979, 4% displayed the pattern of Norwalk
gastroenteritis.
57 This virus was thought to be the cause of more foodborne gastroenteritis than any
single bacterium in the state of Minnesota in 1985.
65 Noroviruses are now the leading cause of
gastroenteritis in the United States with an estimated 23 million cases per year.
17 From several cruise
ship outbreaks in 2002, there were at least 1,786 victims. Up to 21 ship outbreaks occurred during the
same general time period, and the virus appeared to come from unspecified environmental sources.
Of 1,412 outbreaks of foodborne intestinal diseases in England and Wales for the years 1992–1999,
82 (5.8%) were caused by noroviruses (all previously designated SRSVs). From the same survey, 12
of 60 (20%) were traced to fruits and vegetables.
96 Since they have yet to be cultured in the laboratory,
the method of choice is RT–PCR (see Chapter 11).
During the fall of 2001, a rare waterborne outbreak of norovirus gastroenteritis occurred in the state
of Wyoming, and there were around 84 victims. Ground water was contaminated with sewage, which
was the source of the human HuCV. The etiologic agents were identified by use of RT–PCR, which
demonstrated mainly genogroup I, subtype 3; but one stool sample yielded a genogroup II, subtype 6
strain.
86
Among the earliest reported outbreaks that involved noroviruses is one that occurred in 1976 in
England. Between December 21, 1976, and January 10, 1977, 33 outbreaks and 797 cases occurred,