The national picture from 1990 to 1994 is graphed below. Additionally, outbreaks are more likely to promote investigation than sporadic cases. Liquid stool is required for demonstration of virus. Outbreaks of human calicivirus and astrovirus infection tend to affect infants, schoolchildren and the elderly while SRSV outbreaks tend to affect adults. Transmission is principally faecal-oral.
Stored viruses can remain viable for years.
It is thought that infection can be transmitted by aerosols of vomit or faeces, though even in this instance replication is in the gastrointestinal tract and not the respiratory tract. The bivalves then concentrate the viruses within themselves as they filter the contaminated material. All present similarly but vomiting is a more frequent feature of human calicivirus and SRSV infection. Illness lasts 1-4 days and viral excretion generally ceases with recovery, though the immunosuppressed may excrete longterm. You need to submit liquid stool for viral studies.