Then I wouldn't worry about worms unless you are seeing weight loss. I know some like to worm their chickens yearly or more often, but I've kept chickens for almost 15 years and wormed with a wormer twice - once the whole flock and once a single hen.
Boost their immune system with garlic cloves, in feed or water, add herbs like oregano to their feed, and throw some ACV in the water when you can (not in galvinized waterers, though).
Some parasite load is probably normal and can be handled by your chickens. I wouldn't worry about worms as much as things like lice or mites which can take a chicken down quickly.