Generally speaking, the egg whites are mixed with liquor, some type of citrus(usually lemon or lime juice), and sugar. All three of these ingredients have the potential to kill bacteria. So emulsifying these ingredients in a cocktail shaker will kill the potential salmonella that could kill you.
Similarly, citric acid is used for dishes like ceviche, where raw seafood like shrimp is brined in lemon or lime juice.
Also, the risk for a healthy adult getting salmonella from raw egg is pretty low. IMO there is more risk in the garnish tray than anything else behind the bar.
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