Virus Classification

Noroviruses belong to the family Caliciviridae. They are a group of non-enveloped, single-stranded RNA viruses that primarily cause acute gastroenteritis (inflammation of the stomach and/or intestines).

Noroviruses were previously called Norwalk or Norwalk-like viruses. They were named after the original Norwalk strain, which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio in 1968.

The norovirus classificationexternal icon was updated in 2019 and includes the following changes:

  • Noroviruses are now classified into ten genogroups (GI-GX) and 48 genotypes.
  • Some genotypes were reclassified, for example, GII.15 became a new genogroup GIX.
  • The naming for ‘orphan’ P-types was updated to a numbering system, for example, GII.Pe was renamed GII.P31.
  • Dual-typing nomenclature (genotype and P-type) was also proposed; the genotype is reported first, followed by the P-type in brackets such as: GI.1[P1]

A full list of changes can be found on the Human Calicivirus Typing Tool.

Noroviruses were previously called Norwalk or Norwalk-like viruses. They were named after the original Norwalk strain, which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio in 1968.

Variants of the GII.4 genotype (such as GII.4 Sydney, GII.4 New Orleans, GII.4 Hong Kong, etc.) are the most common cause of norovirus illnesses worldwide.