Randomized, double-blinded clinical trial for human norovirus inactivation in oysters by high hydrostatic pressure processing

Abstract

Contamination of oysters with human noroviruses (HuNoV) constitutes a human health risk and may lead to severe economic losses in the shellfish industry. There is a need to identify a technology that can inactivate HuNoV in oysters. In this study, we conducted a randomized, double-blinded clinical trial to assess the effect of high hydrostatic pressure processing (HPP) on Norwalk virus (HuNoV genogroup I.1) inactivation in virus-seeded oysters ingested by subjects. Forty-four healthy, positive-secretor adults were divided into three study phases. Subjects in each phase were randomized into control and intervention groups. Subjects received Norwalk virus (8FIIb, 1.0 × 10(4) genomic equivalent copies) in artificially seeded oysters with or without HPP treatment (400 MPa at 25°C, 600 MPa at 6°C, or 400 MPa at 6°C for 5 min). HPP at 600 MPa, but not 400 MPa (at 6° or 25°C), completely inactivated HuNoV in seeded oysters and resulted in no HuNoV infection among these subjects, as determined by reverse transcription-PCR detection of HuNoV RNA in subjects' stool or vomitus samples. Interestingly, a white blood cell (granulocyte) shift was identified in 92% of the infected subjects and was significantly associated with infection (P = 0.0014). In summary, these data suggest that HPP is effective at inactivating HuNoV in contaminated whole oysters and suggest a potential intervention to inactivate infectious HuNoV in oysters for the commercial shellfish industry.

Fig. 1.

Temporal distribution of subject symptoms and HuNoV excretion. Open squares represent RT-PCR-detected HuNoV-positive stool samples collected from infected subjects during days 1 to 5 postchallenge while admitted to the GCRC and during weekly follow-up visits (days 8, 14, 21, 28, and 35 postchallenge). The distribution of squares (e.g., samples/follow-up visits) is the result of the sample collection time line and does not imply intermittent sample positivity or lack of sample positivity. All of the subjects, with the exception of one (11/12), completed all five follow-up visits and provided five stool specimens; one volunteer missed the day 8 follow-up appointment and provided four stool specimens. Filled diamonds represent self-reported and clinically assessed symptoms of infected subjects. The total number of infected subjects was 12 instead of 13 because one infected subject was not available for follow-up after day 8.