norovirus infectious dose fewer than 100 particles

Norovirus can infect someone with an extraordinarily small dose

Norovirus spreads easily through contaminated food, water, surfaces and close contact. Experiments and outbreak investigations suggest that very small numbers of infectious particles can sometimes establish an infection. That helps explain why the virus spreads rapidly in places such as cruise ships, schools and care homes.

A royal wedding helped create Spain without immediately uniting its kingdoms

The marriage of Isabella of Castile and Ferdinand of Aragon linked two powerful Iberian crowns in the fifteenth century. But their kingdoms retained separate laws, institutions and political traditions. Spain developed through a long process of dynastic and administrative integration rather than becoming one unified state on the wedding day.

Cuba became the first country recognized for eliminating mother-to-child HIV transmission

In 2015, the World Health Organization recognized Cuba as the first country to achieve validated elimination of mother-to-child transmission of HIV and syphilis as public-health problems. This did not mean transmission had become biologically impossible or that no cases could occur. It meant prevention, testing and treatment had reduced transmission to very low levels under established public-health criteria.

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norovirus infectious dose fewer than 100 particles

Norovirus can infect someone with an extraordinarily small dose

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