How Do I Know If I Have Salmonella? When you get sick, it can be hard to know what you have picked up or from where. Many illnesses share the same basic symptoms, especially gastrointestinal conditions, or infections. If you are experiencing fever, diarrhea, and stomach cramps, you might have the stomach flu, or you may have contracted salmonella, one of the most common types of food poisoning. Salmonella is a bacterium that infects the ...