Transmission of Salmonella Bacteria
Human cases of Salmonella are typically acquired through the consumption of Salmonella-contaminated food.
Food is the most common vehicle for the spread of Salmonella, and eggs are the most common food implicated.  As one authority points out, “Studies showed that the internal contents of eggs can be contaminated with [Salmonella], and this contamination has been identified as a major risk factor in the emergence of human illness.” . Part of this risk stems from the variety of ways that Salmonella can contaminate an egg. For example, the FDA has documented the following:
Bacteria can be on the outside of a shell egg. That’s because the egg exits the hen’s body through the same passageway as feces is excreted. That’s why eggs are required to be washed at the processing plant. All USDA graded eggs and most large volume processors follow the washing step with a sanitizing rinse at the processing plant. It is also possible for eggs to become infected by Salmonella Enteritidis fecal contamination through the pores of the shells after they’re laid. SE also can be inside an uncracked, whole egg. Contamination of eggs may be due to bacteria within the hen’s reproductive tract before the shell forms around the yolk and white. SE doesn’t make the hen sick. 
Chicken is also a major cause of Salmonella. Beginning in 1998, the publisher of Consumer Reports magazine has conducted surveys and tested chicken at retail for Salmonella and Campylobacter. Its 2009 study found 14% of broiler chickens at grocery stores to contain Salmonella.  A USDA Baseline Data Collection Program report done in 1994 documented Salmonella contamination on 20.0% of broiler-chicken carcasses . However, in 2009 the same USDA data collection survey showed the prevalence of Salmonella in broiler chickens at 7.5%.  Additionally, turkey carries a lower risk with a prevalence of 1.66%.
While Salmonella comes from animal feces, fruits and vegetables can become contaminated. A common source is raw sprouts, which have been the subject of at least 30 reported outbreaks of foodborne illnesses since 1996.  The U.S. Department of Health and Human Services cautions against consuming raw sprouts under any circumstances: “Unlike other fresh produce, seeds and beans need warm and humid conditions to sprout and grow. These conditions are also ideal for the growth of bacteria, including Salmonella, Listeria, and E. coli.”