They were vaccinated against the illness when they were chicks; they are 5 months old. Can they still get it? How can I treat it? Also, can I still eat their eggs???
Cocci vaccines treat for three common types of cocci generally. Two things can happen: They're exposed to a different variety and come down with coccidiosis because of that. Or they can be overwhelmed with protazoa (or their immune system or healthy bacterial load are insufficient) and still get an infestation with cocci.
I personally would treat if I saw this more than once, if the birds were anything less than perky and active, and if they have diarrhea. I would use Corid rather than Sulmet.
There are also a number of things that can cause blood from the digestive tract, including cecal irritation. In the case where the birds appear healthy and active otherwise with normal droppings, I would just give them PRObiotics to help build up their gut bacteria and assure that the good bacteria are providing competition against fungi/yeast, bad bacteria, and protazoa. That's how they keep the gut healthy.
You have three choices.
My favorite is by using a prepared probiotic, either for human use or livestock. They all use the same basic blend of bacteria, usually lactobacilli and possibly a few other types like bifidobacteria.
My favorite brand is Probios dispersible powder from the feedstore. A small bottle goes for 8 dollars or so and lasts ages in the fridge. At 1/4 teaspoon per bird, it's economical in the long run and very easy to give.
Alternately, you can buy acidophilis capsules or tablets from the vitamin section of your grocery store, drug store, or Walmart. (See their bottom shelf usually.) The powder from breaking a capsule or crushing a tablet is also easy to give and can be used at once capsule/tablet per bird.
You can use either of those even while using -mycin or -cycline drugs.
You also have available the use of plain unflavored yogurt at 1 teaspoon per bird. Many birds love it. Those that don't, you can mix the yogurt with enough water to make a slurry, and then mix that with crumbles or soak bread. Some birds will eat it that way. The cons are that some birds don't like it and you have to feed more. The pros are that it's readily available, even in the middle of the night at 24-hour stores, and some birds LOVE it.. However you cannot use this if you're treating with -cycline or -mycin drugs as the active ingredient.
Unless the birds are lethargic and have diarrhea or you're seeing a lot more of these droppings, I'd just use probiotics daily for a week. Then every other day for a week. Monitor the droppings to make sure they improve or stay stable.
It's possible your birds have been exposed to a variety to which they hadn't developed an immunity before and are building that immunity now and won't need help. I always try to let that happen if possible as the priority. That's where the probiotics help - they won't interfere with the immunity; they'll only enhance it.
Please feel free to email me if you have any questions on my post, or just contact me via this thread. I hope this has helped.