Norovirus is among the most efficient pathogens, and its success is far from accidental.

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First, it takes very few viral particles to cause infection, often fewer than 20.  That means even minimal contamination can be enough to make someone sick.  A microscopic amount left behind on a surface, a hand, or a shared object can still be infectious.

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Second, norovirus is exceptionally stable in the environment.  It tolerates drying, survives on hard surfaces for days to weeks, and is resistant to many common disinfectants.  Routine disinfection that works well for other viruses often isn't enough to inactivate it.  As infection preventionists, we were taught to use bleach to decontaminate surfaces.

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Third, norovirus spreads through multiple transmission routes at once.  It moves via direct person-to-person contact, contaminated food or water, surfaces, and aerosols generated during vomiting.  This makes containment difficult once symptoms begin, especially in shared indoor spaces.  

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Fourth, people are most contagious before they realize what's happening, and many continue shedding virus after symptoms improve.  Add in the fact that immunity is short-lived and strain-specific, and the same person can be infected again.

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Put together, norovirus doesn't need a large outbreak or a dramatic failure to spread.  It thrives on normal human behavior, such as shared bathrooms, busy kitchens, crowded rooms, and imperfect hand hygiene, which is why it resurfaces again and again.

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This combination of low infectious dose, environmental durability, and efficient spread explains why norovirus repeatedly causes outbreaks in various settings.