September 20, 2016 170
"Cuddling kittens can kill you," warns The Telegraph in one of the more alarming headlines to appear in the national press for some time.
But cat lovers can relax – deaths and serious illness from "killer kittens" with so-called cat scratch disease (CSD) are exceedingly rare.
In fact, the study on which this and other headlines are based did not report any deaths, although it estimated 500 people are admitted to hospital in the US each year with the disease.
CSD is caused by bacteria spread among cats by fleas, which can infect humans through scratches and possibly bites from cats.
It causes swollen lymph glands. Some people get more serious infections, leading to inflammation of the brain or the inner lining of the heart.
The study found CSD was most common among children and in southern areas of the US where cats are more likely to be flea-infected. However, it can happen "wherever cats and their fleas are found", the researchers report.
Commonsense measures, such as getting cats treated for fleas and washing hands after handling cats, are likely to reduce the risk of contracting CSD.
And while people with weakened immune systems do need to take extra care around animals, the risk of most people being killed by a kitten is up there with being killed by a falling meteoroid – technically possible, but not something to keep you up at night.
Where did the story come from?
The study was carried out by researchers from the US Centers for Disease Control and Emory University, and was funded by the US Centers for Disease Control.
It was published in the peer-reviewed journal Emerging Infectious Disease on an open access basis, so it's free to read online.
The Telegraph, Mail Online and Metro reported the study with glee, stating that the disease was "potentially fatal".
While this is true, CSD is usually mild and only about 4 in 100 people who contract it need to be admitted to hospital.
Oddly, Mail Online warned about a "rare bacteria" in cats' mouths called Capnocytophaga canimorsus. That bacterium is more commonly associated with dog bites and does not cause CSD, which is caused by the bacterium Bartonella henselae.
The Metro doesn't seem to take the study entirely seriously, complaining of "killjoy doctors" telling us "now we're not allowed to cuddle kittens", concluding that "we're getting tired of this planet".
What kind of research was this?
This epidemiological study used records from a US insurance companies claims database to look at how many people had been diagnosed with CSD between 2005 and 2013.
Database studies can show overall trends, but can't explain what's behind the trends. They are only as good as the accuracy of the records held in the database.
What did the research involve?
Researchers took all records of people diagnosed with CSD who made claims for treatment paid for by insurance companies between 2005 and 2013.
They compared how the numbers changed over time, and looked at which groups of people were most affected, whereabouts, and what proportion had to be treated in hospital.
They summarised the findings to give an overall picture of the disease in the US.
Importantly, the database only looked at people aged under 65 who were in employee-sponsored private health insurance schemes.
The figures don't tell us about people over 65 or those with no private health insurance. The figures only include people in the US, so they also don't tell us how common CSD is in the UK.
What were the basic results?
On average, there were 4.5 outpatient cases of CSD for every 100,000 people every year, and 0.19 cases per 100,000 people each year where patients needed to be admitted to hospital.
Children aged five to nine years were more likely to get the disease, which was also more common among women than men. Older women aged 60 to 64 were most likely to get the disease.
The number of cases fell over the years by about 1 per 100,000 from the start to the end of the study period.
However, the numbers being admitted to hospital as outpatients stayed the same.
The disease was more common in the south of the US, and the researchers found peaks during the autumn and in January.
How did the researchers interpret the results?
The researchers say CSD is "mostly preventable", but "causes a substantial burden of disease nationwide and disproportionately affects children".
They call for "comprehensive flea control for cats", saying that people should wash their hands after handling cats to remove traces of flea faeces that could infect any breaks in the skin.
They say educational efforts should be directed at cat owners, especially those with children in the household or where someone has an immune system deficiency.
The media headlines may sound ridiculous, but taking basic hygiene precautions when handling any animals, no matter how cute they are, is sensible advice.
Although CSD is unusual and does not often cause serious illness, it can be a threat to people with a compromised immune system – for example, those with HIV or taking immunosuppressant drugs.
Scratches and bites from any animal can get infected by bacteria carried by the animal. Even if it's not the bacteria that causes CSD, infected wounds can be painful and cause illness.
It makes sense to teach children in particular how to interact safely with animals to avoid scratches and bites that could get infected.
If the incidence of CSD was the same in the UK, there would be 2,907 outpatient cases in the UK each year.
But this study doesn't tell us whether the incidence is the same here as the US. As the incidence varies between different states in the US, the chances are it will be different in the UK.
There are also some questions about the validity of the figures – we don't know whether all the cases had been positively diagnosed using bacteria analysis, or whether they were probable diagnoses. It's also possible some cases were misdiagnosed as other illnesses.
While cat owners can be reassured that their pets are unlikely to kill them, everyone should know about hand washing and safety around pets.
Links To The Headlines
Cuddling kittens can kill you, warn scientists. The Telegraph, September 19 2016
Cuddling your kitten could KILL you: CDC warns adorable felines carry deadly bacteria that causes brain swelling and heart infection. Mail Online, September 19 2016
Snuggling and kissing kittens could actually kill you, scientists have warned. Metro, September 19 2016
Links To Science
Nelson CA, Saha S, Mead PS. Cat-Scratch Disease in the United States, 2005–2013. Emerging Infectious Diseases. Published online September 19 2016
by GetDoc Team
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