The human caliciviruses have a worldwide distribution being detected in every country they have been sought. In a community-based study in Holland 20% of cases of gastroenteritis were due to noroviruses and 6% to sapoviruses. Noroviruses were detected in all age groups whereas sapoviruses were found only in children with 19% of cases being found in those under 6 months. Seroprevalence studies in developed countries indicate that antibodies to noroviruses are acquired gradually in childhood, and by adulthood 50% are seropositive.1-11-1 In contrast, in some developing countries norovirus seropositivity reaches 100% by 4 years of age. Virtually all adults have antibody to sapoviruses and in Kenya most children are seropositive by 2 years of age. Sapovirus infections appear to be endemic particularly in infants and, in temperate countries, predominate in the cooler winter months often before the rotavirus season. In contrast, noroviruses, while also able to cause sporadic disease, are frequently associated with explosive outbreaks of disease being responsible for up to 80% of outbreaks. These can be community-wide but cause particular problems in health-care institutions such as hospitals and nursing homes. Outbreaks on holiday cruise ships attract great publicity. Finally, food- and waterborne outbreaks occur frequently. Shellfish such as oysters and mussels, which are filter feeders and concentrate noroviruses discharged into the sea in human excreta, are particularly associated with outbreaks. However, other foodstuffs including raspberries and delicatessen food contaminated at source or during preparation also precipitate outbreaks.[14,17] There is recent evidence for a global epidemic of infection with a single GII-4 norovirus which was detected in 55% of unrelated outbreaks in the United States and in seven countries on five continents.1-18-1 Its emergence was related to an increase in the prevalence of norovirus gastroenteritis.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.