MMWR article on 1997 vibrio infections linked to raw oysters
sak2 at cdc.gov
Fri Jun 12 12:53:04 PDT 1998
Hello. Below is the MMWR article (minus Figure 1) regarding
the 1997 Pacific Northwest outbreak of Vibrio parahaemolyticus
infections associated with eating raw oysters. Please refer to the
original website at http://www.cdc.gov/epo/mmwr/mmwr_wk.html
for an official copy of the article.
Public Health Nutritionist
Centers for Disease Control and Prevention
sak2 at cdc.gov
From: Morbidity and Mortality Weekly Report, Vol. 47
(22): 457-462, June 12, 1998.
Outbreak of Vibrio parahaemolyticus Infections
Associated with Eating Raw Oysters -- Pacific Northwest, 1997
During July-August 1997, the largest reported outbreak in North
America of culture-confirmed Vibrio parahaemolyticus infections
Illness in 209 persons was associated with eating raw oysters harvested
from California, Oregon, and Washington in the United States and from
British Columbia (BC) in Canada; one person died. This report summarizes
the investigations of the outbreak, which suggest that elevated water
temperatures may have contributed to increased cases of illness and
highlights the need for enhanced surveillance for human infections.
During July 1-19, the BC Provincial Laboratory received isolates of
parahaemolyticus from nine patients, more than twice the expected number
for July. Because of the high number of isolates identified, the BC
for Disease Control (BCCDC) conducted interviews with the eight patients
who could be contacted; seven had eaten raw oysters during the 24 hours
before illness onset, and one had eaten crabs. On July 30, the BC
of Health (BCMOH) issued a public health alert advising that molluscan
shellfish (e.g., oysters, clams, mussels, and scallops) should not be
raw or undercooked. On July 31, the Vancouver/Richmond Health Board
banned the sale of raw molluscan shellfish in restaurants in the cities
Vancouver and Richmond, BC. These actions were followed by a rapid
decline in the number of new cases. On August 19, the Federal Department
Fisheries and Oceans (DFO) closed all BC coastal waters to the
The BCMOH continued to interview BC residents with
V. parahaemolyticus infections; information was obtained from 42 of the
persons with illness reported during July 1-September 26. Of the 42, a
total of 39 (93%) had eaten molluscan shellfish and 35 (83%) had eaten
or undercooked oysters during the 4 days before onset of illness; 28 had
eaten oysters purchased at restaurants or other food establishments in
and seven had eaten oysters they had harvested. Oysters eaten by ill
persons were traced by BCCDC, the Canadian Food Inspection Agency
and BCMOH to harvesting areas along the BC coast. Samples of oysters
harvested from these areas contained multiple V. parahaemolyticus
at less than 200 colony-forming units (CFU) per gram of oyster tissue.
additional outbreak-related illnesses were reported in BC residents
DFO closed the coastal waters to the harvesting of oysters. The closure
remained in effect until September 12, after which no additional cases
On July 18, on the basis of reports of illness received from local
health departments and from ill persons, the Washington Department of
Health (WDOH) issued an advisory that persons eat only thoroughly cooked
oysters. On August 14, after additional cases had been reported, the
advised commercial harvesters to refrigerate oysters within 4 hours
harvesting, and on August 20, advised the public to thoroughly cook
molluscan shellfish from both commercial and noncommercial sources. On
August 23, the U.S. Food and Drug Administration (FDA) also issued a
statement regarding proper procedures for cooking oysters (1).
WDOH interviewed 54 of the 56 persons who had culture-confirmed V.
parahaemolyticus during May 26-September 9. Of the 54, a total of 48
had eaten molluscan shellfish before becoming ill; 42 (88%) reported
oysters. Product traceback by the WDOH's Shellfish Program determined
35 case-patients had eaten molluscan shellfish harvested in Washington.
August 20, members of the Pacific Coast Oyster Growers Association
voluntarily halted shipments of shell oysters from Washington, and on
August 28, WDOH closed oyster beds in major shellfish harvesting areas.
oyster beds were reopened on September 15, and no additional illnesses
On August 21, the Oregon Health Division (OHD) requested that local
county health departments and microbiology laboratories provide
notification of illnesses associated with or isolations of V.
parahaemolyticus. The request was prompted by an increased number of V.
parahaemolyticus cases detected by the Foodborne Disease Active
Surveillance Network (FoodNet) (a collaboration between CDC, the U.S.
Department of Agriculture, FDA, and seven states for surveillance of
foodborne diseases and related epidemiologic studies) and simultaneous
reports from BC and Washington of a V. parahaemolyticus outbreak
with eating raw or undercooked shellfish.
OHD interviewed the 13 persons reported with culture-confirmed V.
parahaemolyticus infections with onsets during July 19-September 27.
had eaten molluscan shellfish; 10 (77%) had eaten raw oysters. Traceback
the oysters that had been eaten indicated they had been harvested in
near BC (four cases), Washington (four), Oregon (one), and California
(one). On August 26, the implicated oyster harvest bed in Oregon was
by the Oregon Department of Agriculture; only oysters to be cooked could
harvested. On August 28, OHD, in conjunction with the Food Safety
of the Oregon Department of Agriculture, issued a press release warning
persons not to eat raw molluscan shellfish harvested along the Pacific
After closure of the implicated oyster harvest bed in Oregon, no
additional cases associated with eating raw oysters harvested from
waters were reported. The sale of oysters to be eaten raw was
on September 30.
During May-July, the City and County of San Francisco Department of
Public Health reported 11 culture-confirmed V. parahaemolyticus
to the California Department of Health Services (CDHS). On the basis of
these cases, on August 18, San Francisco health officials issued a
advisory recommending that persons not eat raw shellfish and advising
restaurants not to serve raw oysters, clams, or mussels. On August 19,
issued a warning about eating raw oysters, clams, and mussels harvested
the coasts of BC and Washington. CDHS interviewed each of the 83 persons
reported with culture-confirmed V. parahaemolyticus infections with
during June 9-December 9. Of the 83, a total of 68 (82%) reported eating
oysters during the week before onset of illness. Although 59 persons ate
oysters identified through traceback as having been harvested off the
of Washington and BC, nine persons with culture-confirmed illness ate
oysters harvested from Tomales Bay, California (40 miles north of San
During July 20-August 24, culture-confirmed cases of V.
parahaemolyticus infections associated with eating shellfish harvested
Washington or BC also were reported to the state health departments of
(three), Alaska (one), Maryland (one), and Hawaii (one). A total of 209
culture-confirmed V. parahaemolyticus infections were reported
North America during this outbreak. Dates of illness onset ranged from
26 through December 9 (median: August 8) ((|Figure_1|)). V.
parahaemolyticus isolates from ill persons included many different
serotypes, some of which matched serotypes found in oysters. The median
of patients was 39 years (range: 12-85 years); 141 (67%) were male.
Clinical histories were available for 196 persons with culture-confirmed
infection: 194 (99%) reported diarrhea; 172 (88%), abdominal cramps; 101
(52%), nausea; 77 (39%), vomiting; 64 (33%), fever; and 24 (12%), bloody
diarrhea. Of 137 persons providing information on underlying illnesses,
(12%) reported an underlying illness. Two patients were hospitalized;
with V. parahaemolyticus isolated from her bloodstream died.
Mean Pacific coastal sea surface temperatures recorded by the U.S.
Navy ranged from 54 F-66 F (12 C-19 C) during May 13-September 9, 1997
McKenzie, U.S. Navy, personal communication, 1998). These temperatures
2 F-9 F (1 C-5 C) above temperatures from the same period in 1996.
Oysters from implicated harvest sites contained V.
but the number of organisms per gram was often less than 200 CFU. The
highest levels were greater than 11,000 CFU in samples tested by CFIA.
Reported by: M Fyfe, MD, Communicable Disease Epidemiology; MT Kelly,
Provincial Laboratory, British Columbia Center for Disease Control; ST
Yeung, MBBS, Field Epidemiology Training Program, Health Canada; P Daly,
MD, Vancouver/Richmond Health Board; K Schallie, Canadian Food
Agency; S Buchanan, Food Protection Programs, British Columbia Ministry
Health. P Waller, MS; J Kobayashi, MD, Communicable Disease
N Therien, MPH, M Guichard, MS, S Lankford, Public Health Laboratories;
Stehr-Green, DrPH, State Epidemiologist, Washington Dept of Health. R
Harsch, MD, Oregon Health Sciences Univ, Portland; E DeBess, DVM, M
Cassidy, T McGivern, S Mauvais, D Fleming, MD, State Epidemiologist,
Health Div, Oregon Dept of Human Resources. M Lippmann, Communicable
Disease Control Unit; L Pong, Environmental Health Management Section,
and County of San Francisco Dept of Public Health. RW McKay, Food Safety
Div, Dept of Agriculture; DE Cannon, Environmental Health, Shellfish
Program; SB Werner, MD; S Abbott, Div of Communicable Disease Control; M
Hernandez, C Wojee, J Waddell, Div of Food, Drug, and Radiation Safety,
Waterman, MD, State Epidemiologist, California Dept of Health Svcs. J
Middaugh, MD, State Epidemiologist, State of Alaska Dept of Health and
Social Svcs. D Sasaki, DVM, Epidemiology Br, P Effler, MD, State
Epidemiologist, Hawaii Dept of Health. C Groves, MS, N Curtis, Maryland
State Epidemiology and Disease Control, D Dwyer, MD, State
Maryland State Dept of Health and Mental Hygiene. G Dowdle, MSPH,
Communicable Disease Control, C Nichols, MPA, State Epidemiologist, Utah
Dept of Health. Center for Food Safety and Applied Nutrition, US Food
Drug Administration. Foodborne and Diarrheal Diseases Br, Div of
and Mycotic Diseases, National Center for Infectious Diseases, CDC.
Editorial Note: The last large outbreak of V. parahaemolyticus
reported in North America occurred in 1982 and resulted in 10
culture-confirmed cases. Although V. parahaemolyticus outbreaks are
sporadic cases are not infrequent. Most infections are associated with
ingestion of raw or undercooked shellfish harvested from both the Gulf
Mexico and the Pacific Ocean.
V. parahaemolyticus is a gram-negative bacterium that naturally
inhabits U.S. and Canadian coastal waters and is found in higher
concentrations during the summer (2,3). The outbreak described in this
report may have been associated with elevated water temperatures.
V. parahaemolyticus concentrations in oysters and shellfish increase
warmer temperatures, enhanced surveillance at the beginning of summer
lead to earlier recognition and appropriate public health action. Water
temperature monitoring may help determine when oyster beds should be
to harvesting to prevent further outbreaks (4).
Epidemiologic and microbiologic studies conducted during this
primarily implicated eating raw oysters. On the basis of studies
that the infectious dose of V. parahaemolyticus might be greater than or
equal to 100,000 CFU (5), the United States and Canada allow the sale of
oysters if there are less than 10,000 CFU of V. parahaemolyticus per
of oyster. However, adherence to these guidelines did not prevent this
outbreak. Closure of implicated shellfish beds by health officials was
useful; in Canada, additional human illness rapidly declined following a
federally mandated suspension of harvesting of shellfish from BC waters
September. In the United States, shellfish-associated infections
to occur into December.
The mean incubation period for V. parahaemolyticus is 15 hours
4-96 hours). In immunocompetent persons, V. parahaemolyticus causes a
mild to moderate gastroenteritis with a mean duration of illness of 3
Infection can cause serious illness in persons with underlying disease
(e.g., persons who use alcohol excessively or have diabetes,
liver disease, iron overload states, compromised immune systems, or
gastrointestinal problems) (2,6). During this outbreak, most ill persons
had no underlying illness. To reduce the risk for V. parahaemolyticus
other shellfish-associated infections, persons should avoid eating raw
undercooked shellfish. If persons who eat raw or undercooked shellfish
develop gastroenteritis within 4 days of ingestion, they should consult
health-care provider and request a stool culture. Only three states
(California, Florida, and Louisiana) require visible posting of alerts
regarding the risks associated with eating raw oysters at point of
sale (2,7,8). Although assessment of these regulatory educational
strategies have indicated compliance is variable (7), other states might
consider posting such alerts.
V. parahaemolyticus is not a reportable disease in all states.
this outbreak, public health officials in Washington and California and
BC promptly became aware of the outbreak through routine reporting; in
Oregon, although V. parahaemolyticus is not reportable, the outbreak was
detected through an active surveillance program. All states should
making V. parahaemolyticus and other vibrioses reportable; standard
are available from CDC's Foodborne and Diarrheal Diseases Branch,
of Bacterial and Mycotic Diseases, National Center for Infectious
telephone (404) 639-2206; fax (404) 639-2205.
1. US Department of Health and Human Services. HHS news: statement
advising consumers about oysters from the Pacific. World-Wide Web
http://vm.cfsan.fda.gov/~lrd/hhsoyst.html. Accessed June 8, 1998.
2. Hlady WG, Klontz KC. The epidemiology of Vibrio infections in
1981-1993. J Infect Dis 1996;173:1176-83.
3. Morris JG Jr, Black RE. Cholera and other vibrioses in the United
States. N Engl J Med 1985;312:343-9.
4. Shapiro R, Altekruse S, Hutwagner L, et al. The role of Gulf Coast
oysters harvested in warmer months in Vibrio vulnificus infections
the United States, 1988-1996. J Infect Dis 1998 (in press).
5. Sanyal SC, Sen PC. Human volunteer study on the pathogenicity of
parahaemolyticus. In: Fujino T, Sakaguchi G, Sakazaki R, Takeda Y,
International Symposium on Vibrio parahaemolyticus. Tokyo, Japan:
Saikon Publishing Co., Ltd., 1974:227-30.
6. Blake PA, Merson MH, Weaver RE, Hollis DG, Heublein PC. Disease
by a marine vibrio: clinical characteristics and epidemiology. N
7. Mouzin E, Mascola L, Tormey MP, Dassey DE. Prevention of Vibrio
vulnificus infections: assessment of regulatory educational
8. CDC. Vibrio vulnificus infections associated with raw oyster
consumption -- Florida, 1981-1992. MMWR 1993;42:405-7.
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