Twenty-nine norovirus (NV) outbreaks that occurred in daycare centers in Suginami City, Tokyo between November 2004 and December 2005 were investigated. In total, 823 of 2,717 children developed symptoms of NV infection, with an average incidence rate of ca. 30%. Children younger than 2 years old showed higher a incidence of ca. 50%. Among the symptoms, vomiting was seen most frequently in 79% of children, while diarrhea and fever were observed in 43% and 14% of the children, respectively. Detection rates for NV were investigated using the stool specimens of 138 children obtained days after the onset of illness. High detection rates of around 90% were observed on the third to fourth day of illness, followed by a decrease in the rate during later periods. However, NV was detected in more than 50% of the patients even 10 days after the onset of illness. Outbreaks of NV GIIoccurred 3 times in a single daycare center within approximately 7 months. In these outbreaks, 3 children became ill 3 times, and 5 children became ill twice. Genotypes of causative viruses for each of the 3 outbreaks were GII/4, GII/6, and GII/2, respectively. All of the food handlers in the daycare centers where the outbreaks took place were tested for NV. NV was detected in 12 (12%) of 104 food handlers, who worked in 8 (28%) of 29 facilities. Of the 12 NV-positive cases, only 3 cases were symptomatic, whereas 9 cases were asymptomatic.
From the perspective of food safety and risk, we attempted to determine survivability of Newcastle Disease Virus (NDV) in egg products. We investigated the heat inactivation of NDV in egg yolk, and also the inactivation of NDV in mayonnaise. The egg yolks used in this study were SPF-(Specific Pathogen Free)-egg yolk and a typical commercially available type. SPF-egg was derived from un-vaccinated hens. Two types of model mayonnaise were made of salad oil, vinegar, egg yolk and salt, similar to commercial products, using either commercial-egg yolk or SPF-yolk. The NDV strain used in this experiment was the B1/47 (vaccine strain). NDV in commercial egg yolk was inactivated immediately. After model mayonnaise and NDV were mixed, NDV in mayonnaise with commercial egg yolk was inactivated after one day. However, with the SPF-egg yolk, it took 5 days for the virus titre to drop below the detection limit. These findings suggest that NDV in commercial egg yolk may be rapidly inactivated, in part because of antibodies derived from the vaccination of hens against NDV. In addition, these findings suggest that mayonnaise is not a vehicle for the import and export of NDV.