All available rodent species known to be competent hosts for LCMV (capable of becoming chronically infected and shedding virus for up to 9 months)(6, 11, 12) were collected from the remaining rodent stock at the Rhode Island pet store. These species included Syrian hamsters (Mesocricetus auratus),“fancy” mice (M. musculus), and guinea pigs (Cavia porcellus). Although they have not been shown to be competent reservoirs for LCMV,“fancy” rats (Rattus norvegicus) and gerbils (Meriones unguiculatus) also were sampled because of their exposure to the infected rodents. Rodents were sampled and euthanized following approved CDC Animal Care and Use Committee protocols. With a known population size and a LCMV prevalence estimate, the hypergeometric probability distribution was used to determine the minimum sample size needed to provide a 95% chance of detecting at least 1 LCMV infected rodent at each site. The LCMV prevalence was estimated to be 4.7% in Ohio and 4.3% in Arkansas. The Ohio prevalence was based on 4 infected of 85 tested at the Rhode Island pet store; the revised prevalence for Arkansas was based on 9 of 211 positives after data from the Ohio samples were incorporated.

The population sizes (Table 1) included only dwarf hamsters and did not distinguish between the Chinese and Roborovsky dwarf hamsters (Cricetulus curtatus and Phodopus roborovskii, respectively). An agreement was reached with the owner in which≈ 10% of the total population of 140 Roborovsky’s dwarf hamsters was sampled. In this case, the probability of detecting at least 1 positive rodent was 36.5%.