A chronological synopsis of the history of caliciviruses, from discovery to today 


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Nidhi Bhat

Stanford University

Class of 2008 


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Acute gastroenteritis outbreak in Norwalk, Ohio

October 1968: An outbreak of acute gastroenteritis takes place in an elementary school in Norwalk, Ohio. During a 2-day period, 50% of the students and teachers (116/232) developed a gastrointestinal illness, and there was a secondary attack rate of 32% among contacts of primary cases. Lab tests did not reveal an etiological agent.

LID searches for viral agent of gastroenteritis

1969-1972: The Laboratory of Infectious Diseases (LID) at the National Institutes of Health (NIH) embarks on an intense search for a non-bacterial (viral) etiological agent of acute gastroenteritis.

Norwalk Virus is discovered

June 1972: The 27-nm virus-like particle is discovered by the use of immune electron microscopy, from an infectious stool filtrate derived from an outbreak of gastroenteritis in an elementary school in Norwalk, Ohio. It is described as a “small round-structured virus” (SRSV).

CDC creates Vessel Sanitation Program

1975: the CDC creates the Vessel Sanitation Program (VSP) to minimize the risk for gastrointestinal disease among passengers and crew aboard ships by assisting the cruise ship industry in developing and implementing comprehensive environmental health programs. Today, the VSP is an important organization in the surveillance and prevention of norovirus outbreaks.

Sapporo virus first detected

October 1977: Sapporo virus is first detected during a gastroenteritis outbreak in a home for infants in Sapporo, Japan. It is distinguished by its typical surface morphology. 

Hepatitis E virus added to Caliciviridae

1988: Hepatitis E virus is only provisionally classified as a member of Caliciviridae. The virus was first isolated in the 1950's.

Norovirus classified in Caliciviridae

1990: The norovirus genome is finally cloned and sequenced, allowing its classification in the Caliciviridae family.  

Sapovirus genus identified as genetically distinct

1992: Sapoviruses are officially identified as genetically distinct from noroviruses. This is accomplished through the cloning and initial genetic characterization of a genome of human calicivirus with “classical” morphology and comparison with the cloned genome of Sapporo/82/Japan.

International outbreak of single Norovirus strain

1995-1996: “95/96-US” strain of ‘Norwalk-like viruses” cause 60 outbreaks in geographically distant locations within the US and are identified in an additional 7 countries on 5 continents during the same period. 

Hepatitis E virus removed from Caliciviridae

1998: Hepatitis E is removed from Caliciviridae family, after genomic sequencing reveals phylogenetic differences in the non-structural regions of the virus genome.  

Major norovirus outbreak on Mediterranean cruise

November 2003: Spanish authorities close the border with the British colony of Gibraltar before the arrival of a virus-stricken cruise ship carrying some 2,000 passengers. More than 400 passengers on the ship fell ill with a norovirus after the ship left Southampton, England, for a         Mediterranean voyage on Oct. 20. 

Major norovirus outbreak hits United Kingdom

Winter 2007: In the largest norovirus outbreak of the UK in five years, thousands contract viral infection. 100,000 people contract virus per week.