Investigation into an outbreak of gastroenteritis associated with a shellfish harvesting area

At the beginning of 2010, more than 70 cases of gastroenteritis were notified to the Irish Authorities from a number of restaurants in Ireland and the United Kingdom. These cases were associated with the consumption of oysters originating from the same harvesting area. As a result, two producers operating in the harvest area concerned voluntarily agreed to cease production on 10th February and recalled shellfish already on the market.

Oyster directly linked to two illness incidents in Ireland during the outbreak period were sent to the Marine Institute from two restaurants. The levels detected in restaurant samples were 2040 and 2350 NoV GII genome copies per g, respectively. NoV GI was not detected in these samples.

Following the closure of the harvest area samples of oysters were analysed for NoVs in the Marine Institute. The levels of NoV GII detected in oysters sampled on 14th of February from two sites in the harvest area were 1920 virus genome copies per gram and 2880 virus genome copies per gram (table.1).  NoV GI was not detected in these samples.

A faecal sample from an infected consumers received by the National Reference Virus Laboratory in Dublin on 11th of February 2010 was positive for the presence of NoV. Sequencing analysis demonstrated the presence of NoV GII.13 in the faecal sample.

Sequencing analysis conducted in the Marine Institute demonstrated that NoV GII.13 was also present in one of the samples of oysters from the restaurant and in oysters from both sampling points within the harvest area. In addition to GII.13, analysis demonstrated that GII.

Table 1. NoV levels and genotypes detected in oysters during the outbreak period. 

Summary

Levels of NoV in all shellfish samples were significantly higher than background levels normally found in the implicated harvest area.

Sample analysis demonstrated NoV GII.13 contamination in the one faecal sample available, in oysters from one of the restaurant meals and in oysters in the suspected harvest area.

Other genotypes of NoV were also detected in oyster samples from the restaurant meals (GII.3 & GII.4) and in the harvest area (GII.3, GII.4 & GII.12). It is therefore possible that multiple infections may have occurred in infected individuals. 

For further information please contact Bill Dore (bill.dore@marine.ie)