Cat scratch fever is almost never deadly. Out of roughly 22,000 to 24,000 cases that occur in the United States each year, only one fatal infection has ever been reported in medical literature. The vast majority of people recover fully without any treatment. That said, the infection can become serious in specific circumstances, particularly for people with weakened immune systems.
What Cat Scratch Fever Actually Does
Cat scratch fever (formally called cat scratch disease) is caused by a bacterium called Bartonella henselae, which spreads through the scratch or bite of an infected cat. Cats pick up the bacterium from fleas, and even a shallow scratch that barely breaks the skin can transmit it.
The first sign is usually a small raised bump at the scratch site. Within one to two weeks, nearby lymph nodes swell, sometimes to the size of a golf ball. Most people also develop a low-grade fever, fatigue, and headache. The swollen lymph nodes can be tender and uncomfortable, but in otherwise healthy people the infection typically clears on its own within a few weeks to a couple of months.
When It Becomes Dangerous
About 2,000 of the roughly 24,000 annual U.S. cases require hospitalization. That happens when the bacteria spread beyond the lymph nodes and into other organs. Possible complications include:
- Brain inflammation (encephalopathy): Can cause confusion, seizures, or altered consciousness
- Heart valve infection (endocarditis): One of the more serious complications, potentially leading to heart failure
- Liver and spleen swelling
- Eye involvement: Inflammation of the retina and optic nerve, or swelling of the tissue around the eye along with nearby lymph nodes
These complications are uncommon in healthy adults and children. When they do occur, antibiotics are effective at treating most of them.
The Real Risk: Weakened Immune Systems
The people most vulnerable to dangerous outcomes are those with compromised immune systems. This includes people living with advanced HIV, organ transplant recipients on immunosuppressive drugs, and people undergoing chemotherapy.
In these patients, the bacteria can trigger a condition called bacillary angiomatosis: purple to bright red, berry-like skin lesions that bleed heavily if bumped or cut. The infection can also spread to the liver, causing blood-filled cysts in the organ tissue (a condition called peliosis hepatis). The lungs, brain, bones, and spleen can all become involved. Without treatment, bacillary angiomatosis in immunocompromised patients can be life-threatening. With appropriate antibiotic therapy lasting three to four months, most patients recover, though relapses are common.
How It’s Diagnosed
If your doctor suspects cat scratch disease, they’ll typically order a blood test that looks for antibodies your immune system produces in response to the bacteria. A positive result combined with a history of cat exposure and swollen lymph nodes is usually enough for a diagnosis. In some cases, a doctor may want to biopsy a swollen lymph node to rule out other causes like lymphoma, since the swelling can look similar on imaging.
Treatment for Mild and Severe Cases
Most healthy people don’t need antibiotics at all. The infection resolves on its own, though swollen lymph nodes can linger for weeks or even months before fully shrinking. Over-the-counter pain relievers and warm compresses can help with discomfort in the meantime.
For mild to moderate cases where a doctor decides treatment would help, a five-day course of azithromycin is the standard approach. More serious infections that affect the brain or nervous system may require a longer antibiotic course of four to six weeks. Immunocompromised patients with bacillary angiomatosis need three to four months of treatment to reduce the high risk of relapse.
Preventing Cat Scratch Fever
You don’t need to get rid of your cat. The key is controlling the fleas that carry the bacteria in the first place. Talk to your vet about flea prevention products, and be careful: cats are extremely sensitive to certain chemicals, so never apply a flea product without veterinary guidance.
Beyond flea control, a few simple habits make a big difference. Avoid rough play with cats and kittens, since that’s what leads to most scratches. Trim your cat’s nails regularly. Wash your hands with soap and water after handling cats, cleaning the litter box, or gardening in areas where outdoor cats roam. If you do get scratched, wash the wound right away with soap and running water. Supervise young children around cats, since kids are both more likely to play rough and more likely to develop swollen lymph nodes from the infection.
People with weakened immune systems should be especially cautious around cats, particularly kittens, which are more likely to carry the bacteria and more likely to scratch during play.