Characterization of 80 Listeria monocytogenes isolates from urban and natural environments differentiated 7 and 26 EcoRI ribotypes, respectively. Whereas the majority of isolates from the natural environment represented L. monocytogenes lineage II (12 of 13 isolates), urban isolates grouped evenly into lineages I and II (32 and 33 isolates, respectively) and included two lineage III isolates. Multilocus sequence typing of all natural isolates and a randomly selected subset of 30 urban isolates showed a higher overall diversity (Simpson index of discrimination [D] of 0.987 and 0.920, respectively) than did EcoRI ribotyping (D = 0.872 and 0.911, respectively). Combined analysis with ribotype and lineage data for 414 isolates from farm sources, 165 isolates from foods and food-processing environments, and 342 human clinical isolates revealed that lineage I was significantly more common among human (P < 0.0001) isolates, whereas lineage II was more common among isolates from the natural environment, farms, and foods (P < or = 0.05). Among a total of 92 ribotypes, 31 showed significant associations with specific isolate sources. One ribotype (DUP-1039C) was significantly associated with both natural environments and farms. A spatial analysis showed a marginal association between locations in the natural environment positive for L. monocytogenes and a proximity to farms. Our data indicate that (i) L. monocytogenes strains from different sources show a high level of diversity; (ii) L. monocytogenes subtypes differ significantly in their associations with different environments, even though populations overlap; and (iii) a higher proportion of isolates from environmental sources than from human clinical cases can be classified into L. monocytogenes lineage II, which supports the classification of this lineage as an environmentally adapted subgroup.

Results suggest that an important factor contributing to rapid early spread of AI virus infection among commercial poultry farms during this outbreak was disposal of dead birds via rendering off-farm. Because of the highly infectious nature of AI virus and the devastating economic impact of outbreaks, poultry farmers should consider carcass disposal techniques that do not require off-farm movement, such as burial, composting, or incineration.

An outbreak of low-pathogenicity H7N2 avian influenza virus (AIV) in the Shenandoah Valley of Virginia during the spring and summer of 2002 affected 197 farms and resulted in the destruction of over 4.7 million birds. The outbreak affected primarily turkey farms (28 breeders, 125 grow out) with some spillover into chicken farms (29 breeders, 13 grow out, 2 table-egg layers). Although no direct link was established, the strain of H7N2 AIV in this outbreak had a molecular fingerprint that was essentially identical to the H7N2 AIV strain that has circulated in the live bird markets of the northeastern United States for the last 8 yr. After an initial delay caused by lack of viable disposal options, depopulation and disposal, primarily in sanitary landfills, was carried out within 24 hr of detection of a positive flock. Increased surveillance efforts included once-a-week testing of the daily mortality of all poultry farms in the region, testing of all breeder farms every 2 wk, and testing of all flocks prior to movement for any reason. A statistical sampling of backyard flocks and wild birds found no evidence of the virus. The successful eradication of this outbreak was the result of the efforts of a highly effective task force of industry, state, and federal personnel.

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