Chickens can catch infections from wild birds and to prevent this you can add a natural antibiotic to their water. It is called Citricidal and is made from grapefruit seeds. Available from health food shops it is very effective at clearing up any respiratory difficulties such as sneezing, coughing or rasping breathing.
A Gingernut Ranger and Miss Pepperpot perching on top of their Eglu Run
Often if the chickens poo is runny and yellow this is a sign of just such an infection and should be treated as described, the symptoms should clear up in a week. You can continue eating the eggs, because Citricidal is 100% natural.