Infectious outbreaks associated with bivalve shellfish consumption: a worldwide perspective

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Infectious Outbreaks Associated With Bivalve Shellfish Consumption: A

Worldwide Perspective

Potasman I, Paz A, Odeh M

Clinical Infectious Diseases. 2002;35(8):921-928

Oysters, clams, and mussels appear to be increasing in popularity as a

delicacy worldwide, even in the face of bad publicity and diminishing oyster

harvests in North America. So say these investigators from Haifa, Israel.

They provide a useful review of the infections associated with the 8500

species of Bivalvia (phyllum Mollusca). Their key message is that

immunocompromised patients should avoid the risk of consuming raw or

undercooked bivalves, and outbreaks associated with sanitary or processing

breakdowns can be expected to continue despite public health interest.

The investigators conducted a MEDLINE review covering the years 1969-2000,

emphasizing outbreaks reported outside of United States CDC publications in

order to get a more global perspective. In the 27 years between 1970 and

1997, bivalve fisheries have doubled the global catch to 7.4 million tons

annually, with a remarkable 400-fold increase in consumption of clams in

China during this period. Outbreaks have been reported from 12 countries,

including 4 in Asia, but data are lacking from Africa. The largest outbreak

was in Shanghai, where 290,000 people acquired hepatitis A and 47 died after

eating clams. Other large outbreaks have occurred in Japan, the United

States, and Australia, but more worrisome has been the trend for more

outbreaks with time. Oysters account for the majority of outbreaks. Seasonal

distribution of outbreaks is dependent upon the organism involved.

Because bivalves are filter feeders in shallow coastal waters, they are

subject to human sewage. They will effectively concentrate pathogens in

their tissues. Control and monitoring of water contamination in growth beds

has been difficult, particularly for viruses such as hepatitis A and

Norwalk-like viruses (NLV). The general public health approach has been to

warn consumers and physicians of the risk of eating undercooked shellfish.

The most common viral infections are NLVs (calciviruses), hepatitis A,

hepatitis E, poliovirus, astrovirus, and coxsackievirus, and these

infections appear to defy steaming and freezing, are often difficult to

specifically diagnose, and may be hard to attribute specifically to

bivalves. The most important bacterial agents are Vibrio cholerae, V

vulnificus, V parahaemolyticus, and newly described V mimicus. These all

produce varying severity of toxin-mediated gastroenteritis, especially

diarrhea. V vulnificus is noteworthy in its propensity to produce

septicemia, shock, and necrotic bullae on the skin in moderately

immunocompromised patients such as those with diabetes or cirrhosis. Other

enteric bacterial infections such as Salmonella, Shigella, Campylobacter,

and E coli have rarely been attributed to shellfish in recent years, while

one organism gaining recognition has been Plesiomonas shigelloides. Although

Cryptosporidium parvum has been isolated from commercial oysters, there are

few infections linked to bivalves.

Clinicians caring for patients with unexplained gastrointestinal disease

should continue to ask patients specifically about oyster, clam, or mussel

ingestion or exposure. In so doing, they may not only identify the possible

cause of illness of the individual patient, but also alert public health

authorities to potential continuing risk. Certainly they should explicitly

warn their patients not to consume or risk contamination of food with

undercooked bivalves.

ABSTRACT

Clin Infect Dis 2002 Oct 15;35(8):921-8Related Articles, Links

Infectious outbreaks associated with bivalve shellfish consumption: a

worldwide perspective.

Potasman I, Paz A, Odeh M.

Infectious Diseases, Bnai Zion Medical Center, and the Rappaport Faculty of

Medicine, Technion, Haifa, Israel. I.Potasman@...

Outbreaks of shellfish-associated infection have been reported for more than

a century. Since the early 1970s, the global consumption of shellfish has

increased considerably--and with it, the reports of outbreaks of infection.

Most of these reports have originated from the United States, but Europe

and, to a lesser extent, Asia and Australia have also been represented. The

majority of outbreaks have been linked to oysters, followed by clams and

mussels. Hepatitis A virus caused the largest ever shellfish-associated

outbreak, but caliciviruses have caused the highest number of outbreaks;

Vibrio species lead the list of bacterial pathogens. The prognosis of

shellfish-associated infections is generally good, except for outbreaks of

Vibrio vulnificus infection, which have a mortality rate of up to 50% in

vulnerable people. Conventional and molecular techniques should be applied

to better identify the causative agents, thereby enabling more-targeted

control measures in growing, harvesting, and shipping bivalves.

PMID: 12355378 [PubMed - indexed for MEDLINE]