Norovirus gastroenteritis general outbreak associated with raw shellfish consumption in south Italy.

Rosa Prato,Pier Luigi Lopalco,Maria Chironna,Michele Quarto,Giovanna Barbuti,Cinzia Germinario

doi:10.1186/1471-2334-4-37

Abstract

BackgroundDespite Noroviruses (NV, previously "Norwalk-like viruses") being a leading cause of acute gastroenteritis outbreaks, the impact of NV infection is at present unknown and little information is available about strains circulating in Italy. In April 2002 an outbreak of gastroenteritis occurred in the province of Bari (South-east Italy), involving several households.MethodsA retrospective cohort study was performed in order to assess risk factors associated with illness. All households where a case occurred were included in the study. Faecal specimens were collected from ill individuals. NV-specific RT-PCR was performed. Eleven samples of mussels were collected from fish-markets involved in the outbreak. A nested PCR was used for mussel samples.ResultsOne hundred and three cases, detected by means of active surveillance, met the case definition. Raw shellfish eating was the principal risk factor for the disease, as indicated by the analytic issues (Risk Ratio: 1.50; IC 95%: 1.18 – 1.89; p < 0.001). NVs were found by means of RT-PCR of all the stool specimens from the 24 patients tested. Eleven samples of shellfish from local markets were tested for the presence or NVs; six were positive by nested PCR and genotypes were related to that found in patients' stools.ConclusionThis is the first community outbreak caused by NVs related to sea-food consumption described in Italy. The study confirms that the present standards for human faecal contamination do not seem to be a reliable indicator of viral contaminants in mussels.

Highlights

Despite Noroviruses (NV, previously "Norwalk-like viruses") being a leading cause of acute gastroenteritis outbreaks, the impact of NV infection is at present unknown and little information is available about strains circulating in Italy
Descriptive and analytical studies The outbreak occurred during the Easter holidays, between March 31st and April 7th 2002, in the province of Bari (Puglia region, South Italy)
The clinical pattern of the disease was characterised by the presence of vomiting (84.5%), nausea (58.3%), diarrhoea (53.4%), abdominal pain (47.6%), fever (16.5%)

Summary

Methods

Descriptive and analytical studies The outbreak occurred during the Easter holidays, between March 31st and April 7th 2002, in the province of Bari (Puglia region, South Italy). Information, collected by means of a standardised questionnaire, included: 1) demographic individual characteristics such as age, gender, occupation; 2) type of food consumed during the last 72 hours before onset of symptoms; 3) if ill, type, date and time of onset of symptoms. Mussel samples were processed within 12 hours to detect common bacteria by standard methods. Nested PCR was carried out with the use of the primers SR33 for negative strand DNA synthesis and SR48. The 333-bp or 123-bp amplification products from cases and from mussels were subjected to sequencing with PCR primers. The association between raw mussel consumption and illness was significant (RR: 1.50; 95% CI: 1.18 – 1.89; p < 0.001). The attack rate according to raw mussel consumption was 86.3% (69/80)

Results

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