OUTBREAKS OF GASTROENTERITIS IN ELDERLY NURSING-HOMES AND RETIREMENT FACILITIES ASSOCIATED WITH HUMAN CALICIVIRUSES

Eleven outbreaks of acute gastroenteritis, eight of which were in nurs ing homes or retirement facilities, were reported in Virginia during t he winter of 1993-1994. Serum samples (four outbreaks) and stool sampl es (two outbreaks) from involved people were tested for human calicivi rus (HuCV) infection by enzyme immune assays (EIAs) using recombinant Norwalk virus (rNV) and Mexico virus (rMX) capsid antigens and reverse transcription-polymerase chain reaction (RT-PCR). Of the 31 pairs of acute and convalescent serum specimens tested, 24 had a fourfold or mo re titer increase to rMX and 4 responded to rNV. In all four outbreaks , the geometric mean titers (GMTs) against rMX were significantly high er than those against rNV in the covalescent, but not in the acute pha se of illness. The antibody response to rMX among these patients was a lso higher than to rNV (summary mean 32-fold increase vs. 0.7-fold inc rease, respectively, P<.001). Antigen was detected in 5 of 21 stool sp ecimens tested by the rMX EIA, RNA in 12 of 17 stool specimens tested by RT-PCR, and small round structured virus (SRSV) particles in 12 of 21 by electron microscopy (EM); none were positive by the rNV EIA. Seq uence analysis of the RT-PCR-amplified products from the viral RNA pol ymerase region revealed 92-93% amino acid identity with Snow Mountain agent (SMA), 86% with MX, 58-59% with NV, and 31-32% with Sapporo HuCV , suggesting that these viruses belong to the SMA HuCV genogroup. (C) 1996 Wiley-Liss, Inc.