Seafood Safety
Contaminated Species
The following seafoods have been implicated in cases of cholera in the U.S.:
oysters (Klontz et al., 1987), crabs (Davis and Sizemore, 1982), and shrimp
(MMWR, 1986).
Laboratory experiments, using shellfish naturally infected with Vibrios
demonstrate that the bacteria do not depurate well from shellfish (Eyles and
Davey, 1984). The following case of cholera in Colorado supports these
laboratory results. A Colorado resident become ill with cholera after consuming
oysters which were harvested from approved Gulf of Mexico waters, trucked to
Colorado, and stored for several days in recirculation, disinfected artificial
seawater (MMWR, 1989).
Geographic Area
Outbreaks of cholera have been associated with seafood harvested from the
Gulf of Mexico. The type endemic to the Gulf of Mexico (V. cholerae 01,
serotype Inaba, biotype El Tor), is far less pathogenic than its Asian
counterpart (Morris and Black, 1985). The bacterium has been recovered from
Chesapeake Bay water (Colwell et al., 1981), although no illness has been
reported from this area.
Symptoms & Treatment
Symptoms of cholera can begin within 6 hours to 5 days of contact with
bacteria (Morris and Black, 1985). Victims initially experience anorexia,
abdominal discomfort and mild diarrhea. As the illness progresses, the symptoms
may include: watery diarrhea, often grey in color with mucus (called "rice
water"), abdominal cramps, vomiting and dehydration (Shandera et al., 1983;
Klontz et al., 1987). Victims may have as many as 16 stools/day.
Ingestion of 10,000 - 100,000,000 Vibrio cholerae bacteria has been
shown to cause illness in humans (Cash et al., 1979, as cited in Davis and
Sizemore, 1982). Susceptibility to cholera is enhanced in persons who have had
gastric surgery or take antacids, and person who have type O blood tend to
experience more severe cases (Morris and Black, 1985).
El Tor infections (the type endemic to the Gulf of Mexico) are less severe
than other strains (Morris and Black, 1985). For every El Tor case which
requires hospitalization, there are 40 other milder cases (Bart et al., 1970, as
cited in Morris and Black, 1985). Death can occur.
Cholera is treated by aggressive replacement of fluids and electrolytes,
orally and/or intravenously.
Statistics
Cholera was first recognized in the U.S. in 1832. Since there were no
reported cases of cholera between 1911 and 1973, it was believed to be
eradicated. However, in 1973 a case of cholera was reported in the U.S., the
first in over 60 years (Shandera et al., 1983). There were 31 cases of
seafood-borne cholera reported to the CDC from 1973 to 1986 (Adams et al.,
1988). The first outbreak, involving 11 cases, occurred in Louisiana in 1978 and
was associated with eating undercooked crabs (Blake et al., 1980, as cited in
Shandera et al., 1983).
Detection & Prevention
Vibrio cholerae is a naturally occurring bacterium and is not detected
by the presence of traditional indicator bacteria (Hood and Ness, 1982; Colwell
et al., 1981). Prevention of illness can be accomplished by cooking seafood
thoroughly (Boutin et al., 1982). Freezing is ineffective in killing the
bacteria.
Vibrio cholerae, a bacterium which primarily causes
gastroenteritis, is biochemically similar to the epidemic strains of V.
cholerae, but does not agglutinate in V. cholerae 0-group 1 antiserum
(Morris et al., 1981). (This bacterium has also been referred to as,
non-agglutinable vibrio and non-cholerae vibrio.) Some strains of non-01 produce
an enterotoxin similar to cholerae toxin, and some strains appear to produce
more than one toxin (Yasumoto et al., 1983, as cited in Morris and Black, 1985).
Non-01 V. cholerae is commonly found in estuaries, bays and brackish
waters (Blake et al., 1980; Hood and Ness, 1982). Bacterial numbers usually
increase during the summer months (DePaola et al., 1983; Blake et al., 1980). A
survey in the Chesapeake Bay recovered non-01 V. cholerae from water with
salinities between 4 and 17 ppt (Kaper et al., 1979). In contrast, a study of
non-01 Vibrio cholerae levels in the Gulf of Mexico showed an inverse
relationship between salinity and a direct relationship with water temperature
(DePaola et al., 1983). In the gulf study, V. cholerae was recovered from
seawater samples with salinities ranging from 0 to 30 ppt, with highest levels
found at salinities less than or equal to 5 ppt.
Contaminated Species
Non-01 V. cholerae illness is usually associated with consumption of
raw oysters (Morris et al., 1981), and the bacterium has also been isolated from
crabs (Davis and Sizemore, 1982). A 1979 Food and Drug Administration study
found non-01
V. cholera in 14% of the raw oysters screened (Twedt et al.,
1981, as cited in Morris and Black, 1985).
Geographic Area
Non-01 Vibrio cholerae is primarily found in the Gulf of Mexico
(Colwell et al., 1981), but has also been recovered from the Atlantic (Colwell,
et al., 1981) and Pacific Oceans (Blake et al., 1980).
Symptoms & Treatment
Non-01 V. cholerae primarily causes gastroenteritis. Symptoms can
begin within 48 hours of consuming contaminated shellfish (Blake et al., 1908).
The most common symptoms include: diarrhea (as many as 20-30 stools/day),
abdominal cramps and fever. Nausea, vomiting and bloody diarrhea have also been
reported (Morris et al., 1981; Morris and Black, 1985; Blake et al., 1980).
Symptoms can persist for 2 to 12 days (Morris et al., 1981). Patients with
toxigenic isolates have more severe illness that nontoxigenic isolates. Most
strains isolated from ill persons in the U.S. are nontoxigenic (Morris et al.,
1981). Gastroenteritis is treated by oral and/or intravenous rehydration.
Non-01 V. cholerae can also cause septicemia and wound and ear
infections (Blake et al., 1980). Cases of septicemia usually involve individuals
with a preexisting immunocompromising disease. Although the significance is
unknown, non-01 V. cholerae has been isolated from a number of human
sources other than feces including: bile/gallbladder, sputum, appendix,
peritoneal fluid, and cerebrospinal fluid (Blake et al., 1980).
Statistics
In 1979, there were 9 cases of seafood-borne non-01 Vibrio cholerae
gastroenteritis acquired in the U.S. reported to the CDC (Morris et al., 1981).
Detection & Prevention
Since non-01 V. cholerae is a naturally occurring bacterium, it cannot
be detected by the presence of traditional indicator species (Hood and Ness,
1983; Colwell et al., 1981; Eyles and Davey, 1984). Illness can be prevented by
thoroughly cooking shellfish. Freezing shellfish before consumption is
ineffective in preventing illness.
Vibrio parahaemolyticus
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