I sit here right now doing this writeup for you because I have been stricken with a thankfully mild case of food poisoning from something I ate yesterday. Normally I eat things that are cooked but I saw a caesar salad on the menu and because I like those so much I figured I would go for it. Nothing else about my day was different other than that. While I don't know for sure what it is that gave me food poisoning, this does seem the likely suspect and as it turns our, salads are one of the most common ways in which food poisoning is spread.
This higher-than-average probability of getting poisoned by this stuff is compounded when it is served with some sort of meat in it such as chicken, which is common and is what I had in mine last night. If the person making your food uses the same utensils to prepare the raw chicken as they do to handled the cooked chicken, there are a wide array of bad bacterias that they can transfer to your "healthy" meal.
Salmonella and E.coli are just a couple of the wonderful things that you could be accidentally adding to your belly along with the wonderful flavors or romaine lettuce, cheese, and croutons. Also, since salads just generally speaking involved a high amount of uncooked raw veg and fruit, the handling methods of the people preparing it can introduce bacteria from normal human activities that I'd rather not discuss but involves poor bathroom hygiene.
This probability of getting bacteria introduced to your food increases if you are visiting countries where they might not have the same cleanliness standards as in the west, if they have any at all.
Food poisoning is something that I get over very quickly and even though I woke up last night physically shaking from the fever and was barely capable of opening a bottle of water and some paracetamol I am on the mend just a mere 8 hours later. People with less exposure to "overseas bacteria" might not be so lucky though and I have known people that have been laid out for days who couldn't eat anything, struggled to keep even water in their system, and couldn't be further than 10 feet from a bathroom at all times.
It is truly a terrible state to find yourself in.
If you do get an extreme case of food poisoning from a salad or anything else. You might struggle to keep anything in your belly and if that happens it is quite important that you get your hands on some electrolyte powder.
The manufacturer doesn't really matter because they all contain essentially the same thing with a mixture of salts and sugar to expedite the process of getting the hydration into your body that it desperately needs during this time.
At the moment I am just drinking water because after I foolishly had a morning coffee instead, thinking that i am some sort of superhero, I was straight back to the bathroom to do what people do when they are food poisoned. Just stay hydrated and enjoy the weight loss from some mandatory dieting. In my mind this is one of the worst things that can happen to a person while traveling, and when it comes from something so harmless sounding like a salad, it is extra frustrating. A good rule of thumb as far as fruits and veg are concerned overseas is to only get the ones that are still inside of their shell or casing, such as a banana or an orange. Also, maybe just stay away from salads altogether. This is the 2nd time that this has happened to me because of a salad and you'd think I would have learned my lesson.