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In recent weeks, California, home to the largest number of dairy cows in the country, became the 14th state to report infected herds. It is possible that H5N1 may be even more widespread, including in states without reported infections among dairy cows, but a lack of testing has made it difficult to know where the virus is circulating. This bottleneck could be resolved by sampling wastewater as close to dairy farms as possible and using genomic sequencing to confirm the presence of H5N1. Sequencing could also assess any detected virus for mutations possibly conducive for human transmission and enable phylogenetic analyses that can help determine from which species it may have originated. The more H5N1 is allowed to circulate, especially among dairy cows that are clustered closely together in large numbers and with close human contact, the greater the chance the virus could evolve for efficient human spread.
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