Unless you eat all organic meat, a CAFO, or Concentrated/Confined Animal Feeding Operation, was probably the source of all the animal products you've used recently. Meat, milk, cheese, eggs, gelatin and leather, all probably came from one of these factory farms.
You may have heard that the cruel and unsanitary conditions in these feedlots have contributed to the massive overuse of antibiotics. Stressed out animals fed an unnatural diet and living in filth on bare earth or concrete, or cramped into tiny cages, get sick very easily. Very easily. Only large and regular doses of powerful antibiotics make the business model viable.
You may have heard that the manure lagoons generated by too many animals in that small a space pose serious health and environmental risks. The excess nitrogen can poison water supplies and streams, while the pathogen threat is almost too obvious to mention. Manure that should be spread out over a large area to help build healthy soil has been turned into a poison.
Now, it seems that CAFOs may be crucial incubators for Avian Flu, from Worldwatch: