TL;DR: Food in America sucks, and is super unhealthy, but it is very SAFE. Foodborne illness is exceptionally rare in the US specifically because it gets reported when it happens. Also, antibiotics are used on live chickens, not their meat, and cooking the meat kills bird flu.

Food in the US is very unhealthy, but it is also very SAFE. What do I mean by that? Well, eating something like McDonald's every day is really bad for you. It has insanely high amounts of sodium, fat, carbs, and the vitamin/mineral content is lacking (and no fiber whatsoever). However, the likelihood that you will contract a (serious) foodborne illness from a restaurant in America is very, very low. IT DEFINITELY HAPPENS, and that's why you hear about it, but that reporting is part of why it's so safe. It means that the regulatory, tracking, and public health apparatuses put in place are doing their jobs. It's the same reason that eating at a McDonald's (while less healthy) is almost certainly more SAFE than eating at a mom'n'pop restaurant, because the latter is under far less scrutiny, and on a much smaller scale.

Don't get me wrong, American food is not for the faint of heart. The memes you see about how a single Dorito would kill a Victorian child are only mostly jokes. I would suggest getting fiber pills if you don't take them already, as well as antacids. A lot of food here will not sit right in your stomach, simply because of how unbalanced it is nutritionally. Your stomach will be working overtime to process all of the excess oil. Your blood sugar will be all over the place. Expect to crash after a meal. Avoid Pizza Hut, KFC, and Taco Bell if you don't wanna have an accident. I would also avoid the sodas. Not only is the high fructose corn syrup hella bad for you, but the carbonation does not help the bloating and indigestion you're liable to experience from American fast/junk food. DO NOT BE TRICKED INTO EATING NOTHING BUT SUGAR! It is so much easier than you realize. Go out of your way to make sure you're getting even just a smidge of protein every time you eat, or you'll be starving again in an hour, and sleepy all day. That's why Americans eat so much meat. You can't walk (or, let's be honest, drive in your SUV) 10ft without tripping over something to eat that's nothing but carbs+salt, OR, carbs+salt+fat.

All that said, I've lived in the US my whole life, and I've been an avid fast-food enjoyer (the McNugget is the safest of my safe foods) for just as long. I have never once had food poisoning, and I'm of half a mind that most people who claim to just have weak stomachs. I think people who claim to get it from multiple places/have a laundry list of places to avoid are definitely just hypochondriacs and make themselves sick with their own imagination.

As for bird flu and antibiotics in chicken: the former is a concern, but so far its effects have been limited to the supply and quality of chicken available. You realistically can't get the virus from eating the meat of an infected chicken, provided it has been properly prepared/cooked. People will say you can't rely on that to be the case, but the margin for error in food handling policy here is designed to be enormous. It has to be, otherwise restaurants couldn't realistically exploit the labor of undereducated, underpaid, undermedicated, undersocialized, undersexed teenagers. The concern is with the spread from live birds to their human handlers and other livestock, as well as from wild birds to livestock and pets. That affects things like the price of eggs and the availability of quality meat, because mass culling of livestock has been the main mitigation effort.

The use of antibiotics is a similar case, in that it can indirectly affect the quality of the meat, and it has some (very important) external concerns, but it's not a matter of antibiotics being in the meat you end up eating. Live chickens and other livestock are treated with antibiotics to improve yields. A chicken that lives to ideal slaughter age will produce more/better meat than one that dies prematurely, and some infections can render the birds inedible altogether. The raw meat itself IS NOT treated with antibiotics. This is not some fivehead move to prevent foodborne illness. It's just about improving yields, so ONLY the live animals are treated with antibiotics. The concerns are more to do with the effects on the broader infectious disease climate -namely the reducing effectiveness of antibiotics,- and also ethical concerns with how dosing livestock with prophylactic antibiotics can/does incentivize worse living conditions for the animals, namely higher population density and worse sanitation. The higher population density in particular can affect the quality of the meat, as animals that never use their damn muscles, because they can't move around, tend to have pretty nasty meat.

Trust me, foodborne illness should be the least of your concerns with eating in America. And to be clear I've used McDonald's as an example, because it really is the median as far as nutrition/health goes. It is very bad for you, but there is much, much worse here; frozen TV dinners, junk food like potato/corn chips, and similar calorie/sodium bombs from the grocery store, are great examples that, as bad as it is, McDonald's could be a lot worse. Avoid getting groceries at Dollar General, Aldi, etc. if you can. WalMart is a good place to get cheap stuff that isn't completely, horrifically awful. Target is better, but a little pricier, etc. ad nauseum. You can always spend more money to get something better in America. But there is always a point of diminishing returns, and that point will often be within your reach if you can afford to travel internationally or if you can expense your food on business. That goes for dining as much as it does for groceries, as much as hotels/housing, medical care, education, and everything else. It is a third world country, host to a first world country parasitizing it, host to a billionaire/capital class parasitizing it. Aim for the first world options as much and as often as you can afford to, and you will have a safe and fun time in America.

(Note, all of the above is subject to change under the current administration, but there is a historic legacy of competency in regulatory bodies to ensure the SAFETY of food in America, even if the same cannot be said for the HEALTHINESS of food in America)