More than 30 harvest sites were closed over a two month period in France as part of outbreaks linked to eating oysters, according to recently released data.

Because of confirmed norovirus contamination, 31 harvest sites were closed between Dec. 21, 2019, and Jan. 10, 2020, affecting more than 400 companies. This compares to 11 in January 2018 and two in January 2019.

People were infected with norovirus and other enteric viruses such as rotavirus, sapovirus, enterovirus and Aichi virus, according to a study published in the journal Eurosurveillance.

In late December, Santé publique France identified, through its syndromic surveillance system, a large increase in gastrointestinal diseases, primarily acute gastroenteritis and vomiting. This was seen in emergency departments of the Organisation de la surveillance coordonnée des urgences (OSCOUR) network and emergency general practitioners’ associations that provide house calls, SOS Médecins.

Also, an unusually high number of foodborne outbreaks linked to consumption of raw shellfish were recorded by the agency through the mandatory reporting surveillance system.

Much higher numbers
Visits for acute gastroenteritis and vomiting for emergency departments and emergency GP house-calls increased drastically on Dec. 26 and 27 to  3,925 and 4,896 respectively in mainland France and Corsica for people 15 years of age and over, compared with the mean daily number from Dec. 1 to 25 of 1,161.

The 33,500 visits for these symptoms by the two groups in France and Corsica, from Dec. 26, 2019, to Jan. 5, 2020, was above the expected number of 19,750.

For people aged 15 and older, there were 8,957 registered emergency department trips for acute gastroenteritis and 3,386 for vomiting. For the house-call associations, 19,602 acute gastroenteritis visits and 1,553 for vomiting were registered for the same age group.

On Dec. 26 and 27, 2019, 43 outbreaks suspected to be caused by eating raw shellfish, primarily oysters, were reported to Santé publique France through the reporting surveillance system. This number was high compared with previous years. Since 2006, between three and 22 outbreaks linked to raw shellfish have been reported per year.

From Dec. 11, 2019, to Jan. 22, 2020, there were 197 outbreaks linked to consumption of raw shellfish were reported. They affected 1,121 people, of which 25 were hospitalized, but no one died.

Out of stool samples from 32 people, corresponding to 19 outbreaks, norovirus genogroups I (GI), II (GII) or GI/GII were confirmed in 26 cases. Co-infection between norovirus and other enteric viruses was found in 10 of 26 cases: rotavirus once, sapovirus five times, enterovirus three times and Aichi virus once. Enterovirus alone was identified in two cases.

Thirty five strains, isolated from 26 cases, were shown to belong to 10 different norovirus genotypes of both genogroups. A predominance of GI.1 and GII.17 was seen followed by GII.4 Sydney and GII.8.

International element
From Dec. 12, 2019, to Jan. 14, 2020, Luxembourg, Sweden, Denmark, Switzerland, Italy and the Netherlands reported food poisoning due to consumption of raw shellfish from France or norovirus-positive controls on raw shellfish batches, mostly bivalve shellfish, from France.

At least 180 people in Denmark were sickened since the start of the year and 70 were affected in Sweden, although some of these are thought to have eaten Swedish oysters.

Between Jan. 14 and Feb. 10, 18 RASFF notifications were published by Italy, Netherlands, Denmark, Sweden and Finland for norovirus contamination of live oysters from France and products were also recalled in Hong Kong and Singapore.

Previous studies have shown contamination of oysters by norovirus is usually linked to a combination of environmental conditions, including heavy rainfall before harvesting. This can lead to an overflow of sewage treatment stations and fecal contamination of the water.

During December 2019, unusually heavy rainfall was recorded across France and this may have contributed to the contamination of harvest sites by human norovirus.

Researchers also plan to estimate the excess number of cases of gastrointestinal illness during Christmas and New Year using health insurance data that will be available within three months.

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