Inaccurate reporting of cat bite dangers

Friday February 7 2014

“Why even a tiny cat bite could leave you in hospital: Cats’ teeth ‘inject bacteria deep into the joints and tissue’, doctors warn”. The Daily Mail inaccurately claims that one in three people bitten by cats need to go into hospital, and that two-thirds of those people need surgery.

The paper reports on a US study that reviewed the records of 193 people who presented to their hospital (the Mayo Clinic) with a cat bite to the hand during a three year period. They wanted to look at how well they’d recovered, and what factors were associated with them being admitted to hospital.

Overall the majority were middle-aged women, and they found that 30% needed hospital admission and 20% needed surgical treatment to clean out the wound. The important thing to be aware of is that these figures relate only to this specific group of people who presented to the clinic with a hand bite.

However it is important to point out that this may not be a representative sample of cat bite ‘victims’. It cannot tell us what proportion of people who are bitten by a cat but do not feel the need to seek medical attention.

Neither can it tell us anything about bites elsewhere on the body, as this was not assessed.

If you were hypercritical you could make the case that this is not a particularly useful study in terms of analysing the outcomes of cat bites. Perhaps a better approach would have been a survey of cat owners.

Where did the story come from?

The study was carried out by three researchers from Mayo Medical School and the Department of Plastic Surgery at the Mayo Clinic, Rochester, US. No sources of funding were received.

The study was published in the peer-reviewedopen access American Journal of Hand Surgery.

The Mail has vastly over-interpreted the findings of this research and applied them to all people with cats.

For example, they say that one in three people bitten need to go into hospital. The actual finding is that of the people who presented to this specific hospital with a cat bite to the hand over this three year period, one third of them needed to be admitted to the hospital.

It does not mean that of everyone who gets a cat bite in the outside world, a third would need to be admitted. A US study estimated that only 6% of people bitten by a cat require hospital admission.

The research is also only looking at bites to the hand, not elsewhere. 

What kind of research was this?

The authors of this study reviewed the records for their hospital (the Department of Plastic Surgery at the Mayo Clinic) for the three year period between January 2009 and December 2011 to look at all people treated for cat bites to the hand. They wanted to look at how well they’d recovered, and what factors were associated with them being admitted into hospital.

In the US, animal bites are said to account for approximately 1% to 2% of emergency room visits each year. Most bites (60% to 90%) come from dogs, while a smaller proportion come from cat bites (10% to 15%). As the researchers say, while a dog can be mechanically destructive because of the stronger jaws, the sharp teeth of cats can deeply penetrate the tissues with bacteria. The most common bacteria involved in animal bites is said to be Pasteurella multocida which is part of the normal mouth bacteria of many animals, including dogs and cats.

The important thing to realise with such a study is that it is only the experience of a single US hospital, and the people who were treated there. The many other people who may have received cat bites or nips and not sought medical treatment are not included. Neither can it inform about bites elsewhere on the body apart from the hand; nor tell us how common cat bites are, and the likelihood of needing hospital treatment for them. The results also cannot be assumed to reflect the situation in the thousands of other hospitals across the US or in other countries.

What did the research involve?

During the three-year study period, 196 people presented to the hospital with domestic cat bites to the hand or wrist. People with bites above the wrist were excluded, as were those with bites from wild cats (such as lynx and bobcat). Patient characteristics, laboratory findings and follow-up data were collected for each. Not all patients had full data available.

What were the basic results?

The results are presented for 193 people (presumably because data was missing for the other three). Of these people, 69% were female and their average age was 49 years. Half of the presentations came straight to accident and emergency, while the remainder went to their family doctor first. They usually sought medical care around one day after the bite.

Just under 20% of people were admitted to hospital straight away as soon as they presented, while the remaining 80% were initially treated as outpatients with antibiotics (three people received no treatment). Outpatient antibiotic treatment did not work in 21 patients and these patients had to be hospitalised. Overall 30% of all presentations were admitted into hospital, and were then in hospital for an average three days.

The majority of those admitted straight away, and over half of those later admitted after failing antibiotic treatment received surgical treatment to wash out the wound and remove any infected or damaged tissue (overall one fifth of all 193 people).

Complications from infection included abscesses (in six people), involvement of tendons (14 people), involvement of nerves (two people), and loss of joint mobility (14 people).

The researchers’ analyses found that location of the bite over a joint or tendon sheath, and examination findings of redness and swelling, were associated with increased likelihood of hospitalisation.

How did the researchers interpret the results?

The researchers conclude: “Cat bite injuries to the hand can progress to serious infection. The treatment of such infections often requires hospitalization, intravenous antibiotic therapy, and operative treatment. Clinical findings suggestive of the need for hospitalization include location of the bite over a joint or tendon sheath, [redness], pain, and swelling. These findings should increase concern for a severe infection and warrant hospitalization and urgent consultation with a hand surgeon.”

Conclusion

This study reports the experience of the Mayo Clinic in the US over a three year period, during which time 193 people presented with a cat bite to the hand.

Therefore all figures – for example 69% being women, 30% needing hospital admission and 20% needing surgical treatment to clean out the wound – relate only to this specific group of people who presented to the clinic with a hand bite.

  • They cannot tell us how common cat bites are, or what proportion of people who receive a cat bite or nip to the hand in the outside world seek medical attention (as those who did not present to hospital are not included), nor what proportion of all people who have a cat bite to the hand need to have surgical treatment.
  • Even of people who present to hospital with a cat bite to the hand, we don’t know that the findings of this one hospital clinic in the US would be the same as hospitals elsewhere.
  • Neither can it tell us anything about bites elsewhere on the body, as this was not assessed.
  • Though it only looked at domestic cats and excluded wild cats, we don’t know what proportion of these were actually the person’s own cat, or were strays. 

However, despite the media errors in interpretation of the figures, this does not take away from the fact that animal bites can indeed cause serious infection. Aside from minor scratches or nips that have not broken the skin, if you have been bitten it is important to seek medical attention, particularly if there is bleeding or significant pain, swelling or redness.

The wound needs to be thoroughly washed out, and antibiotics are often needed, particularly if the wound is to the hand or face or the wound is deep or needs stitching. Tetanus cover is often needed as well. More severe bites can need surgical treatment to wash out the wound and remove damaged tissues.

Due to the very limited nature of the study population it is difficult to see what relevance this has to UK cat owners.

It is estimated that the majority of cat bites in the UK involve stray, female cats. Only one-in-five cat bites are caused by a pet cat, so hopefully, your pet moggy won’t cause you to spend time in a hospital bed.

Analysis by Bazian
Edited by NHS Choices