Cat scratch fever (formally called cat scratch disease) affects roughly 4.5 out of every 100,000 people in the United States each year, making it relatively uncommon but far from rare. Based on population-scaled estimates, that translates to tens of thousands of cases annually. Because it isn’t a reportable condition, the true number is likely higher than what official databases capture.
How Many Cases Occur Each Year
The most comprehensive look at U.S. case numbers comes from a study of national health insurance claims spanning 2005 to 2013. It found an overall incidence of about 4.5 cases per 100,000 people, with significant variation by region and age. An earlier 1993 analysis estimated about 9.3 cases per 100,000 among outpatients, suggesting the disease has been a consistent, low-level presence in the population for decades.
These numbers almost certainly undercount the real burden. Cat scratch disease is not a condition that doctors are required to report to health authorities, so mild cases that resolve on their own never make it into any database. Many people with a swollen lymph node after a cat scratch recover without ever seeing a doctor.
Who Gets It Most Often
Children between ages 5 and 9 have the highest infection rate of any age group, at 9.4 cases per 100,000. This makes sense: young kids are more likely to play roughly with kittens, get scratched or bitten, and have immature immune systems that take longer to fight off the bacteria.
Geography matters too. Southern U.S. states report the highest rates, at 6.4 cases per 100,000, likely because warmer climates support larger flea populations. Fleas are the key middleman in transmission. Cats pick up the bacterium from infected fleas, and the bacteria can linger under a cat’s claws or in its saliva. When a cat scratches or bites you, the bacteria enter through broken skin.
Seasonal Patterns
Cat scratch disease follows a clear seasonal cycle. Most cases, roughly 87.5%, occur between September and April, with a peak in December. This pattern likely reflects kitten season. Cats born in spring and summer are young, playful, and more likely to scratch during the fall and winter months. Kittens are also more likely than adult cats to carry the bacterium in their bloodstream.
How Many Cats Carry the Bacteria
The bacterium responsible for cat scratch disease lives in cats’ blood, often without causing any symptoms in the cat itself. The percentage of cats carrying it varies enormously depending on location and whether they’re indoor pets or outdoor strays. Studies have found infection rates as low as 4% in some pet cat populations and higher than 60% in others, particularly among stray cats in warm, humid climates in the U.S., Europe, and Southeast Asia.
Kittens under one year old are more likely to be carriers than adult cats. Cats that have heavy flea infestations are also at higher risk, since fleas spread the bacterium from cat to cat. Indoor-only cats with good flea prevention have a much lower chance of being infected.
What a Typical Case Looks Like
The vast majority of cat scratch disease cases follow a predictable, mild course. A small bump or blister appears at the scratch or bite site within 3 to 10 days. One to three weeks later, lymph nodes near the wound swell up, sometimes dramatically. The nodes closest to the scratch are the ones affected, so a hand scratch typically leads to swollen glands in the armpit, while a face scratch might cause swelling in the neck.
Most people also feel generally unwell, with low-grade fever, fatigue, and headaches. The swollen lymph nodes can be tender and warm and may persist for weeks or even months before gradually shrinking. In the typical case, the infection clears on its own without treatment.
Atypical and Serious Cases
About 1.5% of all diagnosed cases are classified as atypical, meaning the infection spreads beyond the lymph nodes. While that percentage sounds small, it adds up. Roughly 25% of children who are hospitalized for cat scratch disease are there because of these atypical complications.
The infection can occasionally affect the eyes, causing a condition where one eye becomes red and swollen alongside nearby lymph node enlargement. It can also reach the liver, bones, or nervous system. In rare cases, particularly in people with weakened immune systems, the bacterium can infect heart valves. These serious complications are uncommon in otherwise healthy people but are worth knowing about if symptoms seem unusually severe or widespread.
How Often People End Up in the Hospital
Hospitalization for cat scratch disease is uncommon. Early national data estimated that fewer than 1 per 100,000 people were discharged from hospitals with this diagnosis each year, while the outpatient rate was about 9.3 per 100,000. That ratio suggests roughly 1 in 10 diagnosed cases was serious enough to require hospital care, though many mild cases likely went undiagnosed entirely, which would make the true hospitalization percentage even smaller.
For those who do need hospital care, it’s typically because of unusually large or painful lymph node swelling that needs to be drained, or because of one of the atypical complications affecting the eyes, liver, or nervous system.
Reducing Your Risk
Flea control is the single most effective way to lower the chance of cat scratch disease. Keeping cats on regular flea prevention breaks the transmission cycle that puts the bacterium on their claws and in their mouths in the first place. Washing cat scratches and bites promptly with soap and water also helps. Avoiding rough play with kittens, especially for young children, reduces the chance of getting scratched. And since the bacterium lives in cat saliva, it’s best not to let cats lick open wounds or broken skin.