MICROBIOLOGY

• Small, non-enveloped, single-stranded positive-sense RNA virus.
• Noroviruses are 1 of 5 genera in the Caliciviridae family.
  
  • Sapoviruses are another genus in the family that also cause acute gastroenteritis.
• Noroviruses are grouped into genogroups, numbering six currently known (I, II, and IV cause human infections), further divided into genetic clusters.
  
  • Genogroup II, genotype 4 (II.4) is most commonly associated with outbreaks and severe disease.
  • Genogroup I generally causes less severe disease and a lower attack rate partly because of an association between ABO blood type and infection.
  • Total 25 genotypes known among GI, GII and GIV.
• Previously known as "Norwalk-like viruses."