Table 1.
Prevalence studies of norovirus (NoV) in bivalve mollusks.
| Country | Type of Shellfish | Production Areas | Dates of Sampling | NoV Prevalence (Total Number of Analyzed Samples) | Prevalence of NoV GI | Prevalence of NoV GII | Data on Viral Load a → % Positive Samples |
Ref. |
|---|---|---|---|---|---|---|---|---|
| EUROPE | ||||||||
| Belgium | Oysters, clams and mussels (raw and frozen) | Seafood company | 2012–2013 | 32.3% (n = 65) | 24.6% | 13.8% | 3.3 × 103–1.4 × 104 →42.6% | [44] |
| France | Oysters | ND | ND | 14% (n = 78) | ND | ND | ND | [13] |
| France | Mussels | Thermally-treated shellfish; imported from different countries as frozen | 2008 | 21.7% (n = 83) | 8.4% | 11.4% | ND | [42] |
| France | Oysters | A and B | 2010–2011 | 9% (n = 387) | 1.6% | 8.3% | Range: 9.3 × 101–2.2 × 102 | [27] |
| Ireland | Oysters | A and B | 2005–2007 | 37.1% (n = 167) | ND | ND | ND | [45] |
| Ireland | Oysters | A and B | 2009–2011 | 88.1% (Nov-March) 50.9% (April-Oct) (n = 113) |
ND | ND | Average Nov-March: 1.3 × 103 Average April-Oct: 2.1 × 102 |
[13] |
| Ireland | Oysters | Point of sale | 2015–2016 | 84% (n = 25) | ND | ND | Geometric mean (95% CI): 69 (40–120) | [30] |
| Italy | Clams and mussels (before and after depuration) | A and B | 2005–2006 | 8.3% (0% in depurated samples) (n = 120) | 3.3% | 5% | ND | [32] |
| Italy | Clams, mussels and oysters | B | 2008–2009 | 51.4% (n = 70) | 37.1% | 48.6% | ND | [46] |
| Italy | Clams, mussels, oysters and others | A and B | 2008–2012 | 51.5% (n = 336) | 26.5% | 45.4% | Average A area: 3.1 × 102 Average B area: 1.9 × 103 |
[47] |
| Italy | Mussels and razor shells | A and natural beds | 2011–2012 | 18.7% (n = 59) | 6.8% | 11.9% | ND | [48] |
| Italy | Clams, mussels, oysters and others | A and product at retail | 2003–2011 | 4.2% (n = 4359) | ND | ND | ND | [49] |
| Italy | Mussels and clams | A and B, as well as shellfish from registered and unregistered retailers (street vendors) | 2007–2010 | 57.5% (n = 163) | 29.4% | 56.4% | ND | [33] |
| Italy | Mussels | A and B | 2014–2015 | 23.1% (n = 108) | 9.3% | 20.4% | Average GI: 1.0 × 102 Average GII: 0.6 × 102 (range 1.2 × 102–5.8 × 107) |
[50] |
| Italy | Mussels, clams, oysters, and others | A and B | 2013–2015 | 14.2% (n = 253) | 1.6% | 12.2% | ND | [51] |
| Montenegro | Mussels | A and B | 2015–2016 | 43% (n = 72) | 19.4% | 37.5% | Range GI: 10–1.2 × 103 Range GII: 10–1.2 × 104 |
[31] |
| Netherlands | Oysters | Point of sale | 2015–2016 | 31% (n = 29) | ND | ND | Geometric mean (95% CI): 49 (40–91) | [30] |
| Spain (Galicia) | Clams, cockles, mussels | B and C | 2005 | 56% (n = 41) | 7.3% | 53.7% | Range: 5.6 × 101–1.5 × 104 | [52] |
| Spain (Galicia) | Mussels | B and C | 2010–2012 | 49.4% (n = 81) | 8.6% | 30.8% | Range: 5.9 × 103–1.6 × 109 | [34] |
| Spain (Galicia) | Clams, cockles, mussels | B | 2011–2012 | 45.2% (n = 168) | 32.1% | 25.6% | <102→9.5 % 102–103→31.6 % 103–104→37.9 % 104–105→20 % >105→1 % |
[35] |
| UK | Oysters | B | 2004–2006 | 48% (n = 14) | 41.4% | 40% | ND | [28] |
| UK and Scotland | Oysters | 39 areas, A, B and C | 2009–2011 | 76.2% (n = 844) | 67.4% | 54.5% | <102→63.5 % 102–103→21.9 % 103–104→13.5 % |
[29] |
| UK | Oysters | Point of sale | 2015–2016 | 71.7% (n = 434) | ND | ND | Geometric mean (95% CI): 78 (40–277) | [30] |
| ASIA AND AUSTRALIA | ||||||||
| Australia | Oysters | Growing areas with risk of pollution | 2010–2011 | 1.7% (n = 120) | 0% | 1.7% | ND | [53] |
| Australia | Oysters | All major oyster harvest areas within the country | 2014–2015 | <2% (n = 300) | 0% | 0% | ND | [54] |
| China | Clams, mussels, oysters and others | Retail | 2009–2011 | 13.3% (n = 840) | ND | ND | <102→37.4% 102–103→46.1% 103–104→13.9% >104→2.6% |
[55] |
| Japan | Oysters | A and B | 2002 | 9% (n = 191) | 7.4% | 1.6% | <102→35.3 % 102–103→41.2 % 103–104→17.6 % >104→5.9 % |
[56] |
| Vietnam | Oysters | ND | 2016–2016 | ND (n = 34) | 79% | 42% | Max GI: 2.4 × 105 Mas GII: 2.3 × 104 |
[18] |
| AFRICA | ||||||||
| Morocco | Clams, cockles and oysters | ND | 2006–2010 | 29.9% (n = 77) | 20.8% | 18.2% | Average clams: 2.1 × 102 Average cockles: 2.8 × 102 |
[57] |
| UNITED STATES (US) | ||||||||
| US (Louisiana) | Oysters | A and B | 2013 | 0.2% (n = 440) | 0% | 0.2% | 3.4 × 103 | [58] |
| US | Oysters | ND | 2007 | 3.9% (n = 338) | 1% | 2.9% | ND | [59] |
a Viral load is expressed as genome copies per gram of digestive tissue; ND: Not determined; CI: confidence interval.