Several issues need to be considered regarding our fi nding of low virus isolation rates compared with realtime RT-PCR-positive rates. Virus isolation detects viable virus, whereas real-time RT-PCR detects small stretches of nucleic acid, even if the larger genomic RNA is inactivated. This makes real-time RT-PCR a more sensitive detection tool but does not provide information about virus viability. Samples obtained from the environment may be less suitable than animal samples for virus isolation techniques. Organic matter, duration and temperature of exposure, and humidity can all affect virus survival outside the animal host (22) . Three studies conducted in LBMs tested environmental samples and bird samples by using virus isolation (8, 10, 23) . Only 1 of these studies stratifi ed the avian infl uenza detection rates by type of sample (bird vs. environment) (8) ; that study found that from 12 LBMs, 11 were positive for avian infl uenza in bird samples compared with only 5 positive in environmental samples. These results were based on a small sample of LBMs, and real-time RT-PCR was not conducted. Therefore, to determine the suitability of virus isolation for environmental samples, we recommend that future studies compare real-time RT-PCR-positive rates to virus isolation rates in both environmental swab and bird samples.