Salmonella infections in resource-rich countries are almost always acquired by ingestion of contaminated food. This is because:
- There is a large reservoir of Salmonella in animals, especially poultry.
- Salmonella is relatively sensitive to stomach acid, so only large numbers of bacteria can establish infection.
- Salmonella may be shed in the feces for several weeks after an infection has resolved, facilitating food contamination.
- Water treatment suppresses infection due to drinking contaminated water.
- All of the above statements are correct.
In resource poor countries, Salmonella can be spread by contaminated water. In discussing routes of infection, it is interesting to contrast Salmonella with Shigella infections. Shigella is much more resistant to stomach acid, and so infections can be caused by a small number of organisms. This greatly facilitates spread of shigellosis in settings such as day care centers, where fecal-oral transmission occurs via contaminated surfaces.
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