Molecular epidemiology of calicivirus infections in Norway

The national reference laboratory for calicivirus diagnostics monitors the epidemiology of calicivirus infections in Norway. During winter 1998-1999, 406 fecal samples were received from patients with suspected calicivirus infection. Of these, 76 (19%) were calicivirus positive by a nested reverse transcription-polymerase chain reaction. A number of alternative PCR designs were employed to disclose false negatives, but none were found. One half of the PCR positive samples were sequenced in order to investigate whether various cases represented the same outbreak, and to what extent a single or multiple subtypes were responsible for the morbidity during this season. The sequence data revealed that the majority of cases represented a genotype related to the Lordsdale strain, whereas the remaining cases seemed more sporadic. Most often, samples from particular outbreaks were highly homogeneous. However, in a few cases, samples connected with the same outbreak proved to contain epidemiologically independent strains.