Epidemiology of calicivirus infections in Sweden, 1994-1998

Outbreaks of acute gastroenteritis are frequently caused by caliciviruses. Electron microscopy was used to search for these viruses in fecal samples f rom patients with acute gastroenteritis. Of 5800 samples collected and anal yzed from November 1994 to June 1998, 3700 were associated with outbreaks. A total of 676 outbreaks were analyzed, and viruses were found in 67%. Cali civiruses, usually Norwalk-like viruses (NLVs), were found in 407 (89%) of 455 outbreaks, while Sapporo-like viruses were identified in nine outbreaks , including six that were suspected to include foodborne transmission. Sixt y percent of the 1041 patients with calicivirus infections were between 70 and 90 years of age. Food- and waterborne infections were associated with 6 6 calicivirus outbreaks. Virus-positive outbreaks were documented mainly du ring winter and spring. The longitudinal survey showed that caliciviruses, and especially the NLVs, cause most nosocomial and community-associated out breaks in Sweden.