I've noticed several topics about cat attacks on chickens over the last few months here on BYC. This thread is not intended to talk about if cats attack, when they attack, how to prevent, etc... That is all discussion that is already happening in other threads. Check out the Predator and Pest forum if you want to discuss these issues. This is just some HEALTH information for those that have experienced an attack by a cat, or even have a nice cat that has gotten mischievous around your chickens or chicks. Or even if you have a kitty that 'grooms' your chickens...
Note: this thread isn't meant as a 'scare' thread, but simply to share some knowledge that is not always commonly known. As with all knowledge, use it or not, it is your choice!
It is very important to remember that 90% or more of domestic cats (which as a species includes feral cats too!) carry the Pasteurella bacteria in their mouths. Dogs can carry and transfer this bacteria too, but with much less frequency than cats. Small predators such as raccoons can also carry this bacteria.
Why is this important?
The Pasteurella bacteria, once transferred to a small animal (but especially birds) usually multiplies rapidly, can become systemic quite quickly (cause a serious infection), and for some birds is commonly fatal (approximately 50-60% of the time) unless a course of antibiotics is administered quickly (within 24 hours).
A large fowl, full grown hen or rooster might be able to fight off this infection if they are otherwise healthy, but it can cause serious problems for smaller birds, chicks, and birds with weakened immune systems. Even healthy, adult birds can succumb!!
In this way, even a small puncture from cat's teeth or a scratch can be quite harmful indeed. For some birds it can be fatal. Even if the scratch or bite is superficial is not in itself a bad injury!
Cats are especially deadly predators to small animals (especially wild birds), which often perish within two or three days of escaping a cat's attack, even if the cat did not injure it fatally or "only" had it in its mouth and didn't even bite at all.
Given this knowledge, it is important to monitor any birds that have been attacked (or groomed by/played with) by a cat, or other small predatory animal such as raccoons. If you have an antibiotic on hand, it would be wise to administer it immediately after such an attack. From an article below (emphasis mine):
Cat bites may range from tiny puncture wounds to lacerations. The muscle underneath a puncture wound may be lacerated due to the action of the teeth in immobile muscle (relative to the skin). Many wounds cannot be detected with the naked eye and the need for antibiotics may not be recognized in cases where there is no evidence of a puncture wound or scratch . Septicaemia is a common sequel to a cat bite, while other routes of infection have also been suggested. Birds may ingest organisms from cat saliva-coated feathers during preening leading to gastrointestinal disease and septicaemia . Cats carry Pasteurella multocida on their gingival tissue and teeth and antibiotics are therefore always indicated in any bird attacked by a cat , . In addition to Pasteurella spp, a mixed aerobic/anaerobic population has been recovered from the majority of cat bite wounds . Selecting the right antibiotic (or antibiotic combination) is therefore of vital importance. Penicillins have been cited as the antibiotic of choice due to their efficacy against P. multocida  and their broad spectrum of action. Fluoroquinolones, such as the much-favoured enrofloxacin (Baytril) should not be used on their own as they lack action against anaerobes and provide incomplete coverage against Streptococci spp. For infected bites clavulanate-amoxycillin or combination therapy with penicillin, or clindamycin, and a fluoroquinolone is recommended. Ideally culture and sensitivity testing should be performed, but this will often be impossible for time and cost reasons.
Bite wounds should be aggressively cleaned and flushed with saline or 0.05% chlorhexidine . Flushing may need to be repeated. Puncture wounds can be left open to drain but lacerations should be dressed to protect the underlying tissues. Some puncture wounds may need to be opened up to facilitate access to the underlying traumatized tissues.
Where the pectoral muscles have been lacerated, aggressive cleaning and debridement is indicated under general anaesthesia. Torn, necrotic muscle should be removed and the wound packed with a hydrogel. A hydrocolloid dressing (eg Duoderm Extra Thin) can be applied over the wounds to provide additional protection. The wounds should be reassessed after 24 to 48 hours and a decision made as to whether wound closure is appropriate (Figure 15 to Figure 18)."Even birds with trivial wounds caused by cats must be classified as emergency patients. The risk of an infection after a cat bite is about 56%. For treatment of a Pasteurella multocida infection Doxycycline should be used."
Dosage of antibiots depends on the weight of your bird-- follow label instructions or consult with a local vet. If you don't have one, many avian vets are understanding about home-care for chickens and will give the dosage for you, even if you are not a patient of theirs. As always, I am not a veterinarian and you should always consider the advice of a trained avian veterinarian over mine!!
(The Pasteurella bacteria is why some people have some bad reactions to cat bites/scratches as well. Many of us fight the bacteria off and see no ill effects, but those that do not can have symptoms ranging from mild swelling and pain to a serious infection. Infection is also more common in those with weakened immune systems).
Some sources, just so you don't think I'm nutters.
Please feel free to add any information you might have, or correct me if I'm wrong. Feel especially welcome to share this to anyone you know that has problem cats around their flock...!! This might save the life of some chickens out there.