Background Sapporo-like human caliciviruses (Sapp HuCVs) constitute one genus in the virus family Caliciviridae. Recently, an antigenically distinct variant within Sapp HuCVs was characterized.Aim To describe the virologic features of an outbreak of infection by this Sapp HuCV in a Houston, TX, child care center (CCC).Methods Attendance and occurrence of diarrhea and vomiting were recorded daily. Stool specimens were collected weekly and when diarrhea occurred. Viral RNA was extracted from stool specimens and the presence of the Sapp HuCV was determined by reverse transcriptase-polymerase chain reaction(RT-PCR) using type-specific primers in the RNA-dependent RNA-polymerase region. Results A total of 254 stool specimens were collected in the outbreak period (12/89-1/90) from 35 children in the 3-room CCC. 77 (30%) of the 254 specimens and 30 (86%) of the 35 children were positive for excretion of the Sapp HuCV. 7 (23%) of the excreting children had diarrhea with the Sapp HuCV infection episode. Duration of virus excretion ranged from 1 to 34 days (mean=5.2d), although infection-related diarrhea persisted 1 to 4 days (mean=1.8d). 17 children had two infections in the outbreak period. The pattern of excretion suggested that movement of children from one room to another might be involved in virus spread. Sequencing of one RT-PCR product confirmed the identity of the outbreak strain (99% nt identity with prototype HuCV/Houston/27/90/US). Conclusions In this outbreak studied by RT-PCR, a high infection rate and longer virus excretion was found in comparison with previous descriptions of Sapp HuCV outbreaks characterized by EIA (mean 5.2d and longer duration of 34d vs. 1.5d and 17d, respectively previously). Asymptomatic, persistent virus excretion might be responsible for the high prevalence and early age of Sapp HuCV antibody acquisition in children attending child care centers. Our findings suggest that person-to-person spread rather than single source exposure was involved in virus transmission.
