Snow Mountain Agent Gastroenteritis From Clams

Abstract

A 1983 investigation of two clambake-related gastroenteritis outbreaks in Rochester, New York, showed that 84 (43%) of 196 persons interviewed had an acute illness characterized by watery diarrhea, vomiting, and abdominal cramps. None of the ill persons were hospitalized or had complications. Illness was associated with eating raw (p = 0.002) or baked (p less than 0.01) hard-shell clams, with the risk of illness increasing with the total number of clams consumed (p less than 0.01). The median incubation period and duration of illness were 36 and 44 hours, respectively. Stool samples obtained 2-4 days after onset of illness were negative for commonly recognized bacterial and viral pathogens. However, of 31 persons whose stools were tested, the stool of only one ill person was positive by enzyme-linked immunosorbent assay for the Snow Mountain agent, one of the Norwalk-like viruses. Paired serum specimens from six (67%) of nine ill and two (29%) of seven well persons showed a fourfold or greater rise in antibody titer to Snow Mountain agent. Persons who ate clams were more likely to seroconvert to Snow Mountain agent (eight of 12) than were those who did not eat clams (zero of four) (p = 0.04). The clams were harvested off the coast of southern Massachusetts in late October, when harvest waters were documented to be contaminated by untreated municipal sewage. This report describes the first documented outbreak of shellfish-associated gastroenteritis attributed to Snow Mountain agent of which we are aware.

Outbreaks of food-borne and waterborne viral gastroenteritis

“…In contrast, an outbreak of food-borne Snow Mountain virus in a nursing home was accompanied by the sudden onset of illness among 41 residents within 48 h of an implicated meal, with subsequent person-to-person transmission to over 100 other residents and staff (37). In another study, a similar epidemiologic appearance was reported for sequential outbreaks of astrovirus type 1-and rotavirus-caused gastroenteritis among geriatric residents of a large psychiatric hospital in which transmission by food was not implicated but could not be thoroughly assessed (81 (47,49,98,110). Oysters, clams, and other shellfish filter virus particles from contaminated water and accumulate them in their tissues.…”

“…Serologic rises in antibody titer to Norwalk-like viruses have been demonstrated by IEM, RIA, and EIA (8,36,37,46,93,110). An immunoblot assay has recently been developed for one Norwalk-like virus (SRSV-9) in Japan (52).…”

“…Similarly, Norwalklike viruses were detected in fecal specimens by IEM in outbreaks from Marin County, California, and Snow Mountain, Colorado (28,93). An EIA for Snow Mountain virus detected virus particles in fecal specimens from a clamassociated outbreak and from an outbreak in a retirement home (37,110).…”

“…Norwalk virus was subsequently shown to be a frequent cause of outbreaks of food-borne and waterborne AING in the United States (20,40,69,76). From 1978 through 1982, the clinical and epidemiologic features of outbreaks of foodborne and waterborne Norwalk virus infection were characterized (4, 43, 44, 47, 48, 70-72, 74, 108, 115); also, during the 1980s, an increasing variety of viral agents were implicated as causing outbreaks of food-borne or waterborne illness (8,9,26,36,45,46,60,61,73,86,105,110). The clinical aspects of these illnesses and the epidemiologic aspects of the outbreaks resembled those caused by Norwalk virus.…”

Production of a monoclonal antibody against the Snow Mountain agent of gastroenteritis by in vitro immunization of murine spleen cells.

“…The Norwalk agent has been established through the use of these assays as an important cause of gastroenteritis throughout the world, and serologic surveys have shown a high prevalence of Norwalk antibody in both developed and developing countries (9). More limited studies with SMA have associated this agent with outbreaks of gastroenteritis in various areas of the continental United States (10)(11)(12) and have shown that >50% of adults who have been tested have serum antibody to this virus (7).…”