In medical contexts, CSD most commonly stands for cat scratch disease, a bacterial infection you can get from a cat’s scratch or bite. About 4.5 out of every 100,000 people in the United States are diagnosed with it each year, making it one of the more common infections transmitted from animals to humans. The abbreviation CSD can also refer to a couple of less common medical terms, which are covered briefly below.
Cat Scratch Disease: The Basics
Cat scratch disease is caused by a bacterium called Bartonella henselae, which lives in the bloodstream of infected cats. Cats pick up the bacterium from fleas, and they pass it to humans through scratches, bites, or by licking an open wound. Kittens are more likely to carry the infection than adult cats, partly because they scratch more during play and are more likely to be flea-infested.
The infection follows a fairly predictable pattern. Within a few days of being scratched, a small red bump (sometimes a blister) appears at the scratch site. This is the inoculation lesion, and it can last one to three weeks or sometimes longer. One to three weeks after that initial bump appears, lymph nodes near the scratch swell and become tender. If a cat scratched your hand, for example, the lymph nodes in your armpit or elbow area would likely be the ones affected. A low-grade fever and general tiredness often come along with the swollen nodes.
Children between ages 5 and 9 have the highest infection rate, at roughly 9.4 cases per 100,000. People living in the southern United States are also diagnosed more frequently. Most cases are handled entirely in an outpatient setting, though a small number of patients, particularly men between 50 and 64, are more likely to need hospitalization.
How CSD Is Diagnosed
Doctors typically suspect cat scratch disease based on the combination of a recent cat scratch, a bump at the scratch site, and swollen lymph nodes nearby. Blood tests can confirm the diagnosis by detecting antibodies against Bartonella henselae. An antibody level above a certain threshold is considered diagnostic, though results can sometimes be ambiguous if the infection is very early.
When blood tests are inconclusive, a tissue sample from a swollen lymph node can be tested using a DNA-based method (PCR) that identifies the bacterium’s genetic material. This approach is extremely reliable when it finds the bacterium, with near-perfect accuracy, but it misses some cases. Sensitivity ranges from about 40% to 76% depending on how the tissue was preserved and processed. In practice, many straightforward cases are diagnosed on clinical grounds alone, without needing a biopsy.
Symptoms Beyond the Typical Case
About 95% of people with cat scratch disease get the standard picture: bump, swollen nodes, mild fever. The other 5% develop atypical complications that can look quite different. One of the more distinctive is Parinaud oculoglandular syndrome, which happens when the bacterium enters through the eye (usually from rubbing your eye after handling an infected cat). This causes a red, irritated eye on one side along with swelling of the lymph node just in front of the ear on the same side.
Other uncommon complications include inflammation of the retina (neuroretinitis), brain inflammation (encephalitis), bone infections, heart valve infections, and liver or spleen lesions. Prolonged unexplained fever can also be the only sign. Older adults are more likely to develop these atypical presentations, occurring in roughly a third of elderly patients compared to about 14% of younger ones.
Treatment and Recovery
For most healthy people, cat scratch disease resolves on its own within two to four months without any specific treatment. The swollen lymph nodes gradually shrink, though they can remain tender for several weeks. Over-the-counter pain relievers and warm compresses can help with discomfort during that time.
Antibiotics are typically reserved for people with more severe symptoms, those with weakened immune systems, or cases involving atypical complications. When antibiotics are prescribed, the course is usually short. People with compromised immunity, such as those undergoing chemotherapy or living with HIV, are at higher risk for serious or prolonged infection and are more likely to need treatment.
Preventing Cat Scratch Disease
The most effective prevention strategy is flea control. Since cats acquire the bacterium from fleas, keeping your cat on a regular flea prevention regimen dramatically reduces the risk. Beyond that, avoid rough play with cats (especially kittens), wash any scratches or bites promptly with soap and water, and don’t let cats lick open wounds or broken skin. You don’t need to give up your cat if you’re diagnosed with CSD, but controlling fleas and handling scratches carefully goes a long way.
Other Medical Meanings of CSD
While cat scratch disease is by far the most common medical use of the abbreviation, CSD occasionally appears in two other contexts.
Cortical Spreading Depression
In neurology, CSD refers to cortical spreading depression, a slow wave of electrical activity that sweeps across the brain’s surface. During this wave, a large group of brain cells depolarizes (essentially fires all at once) for about a minute, then goes electrically silent for several minutes. This wave is the physiological event behind migraine aura, the visual disturbances, tingling, or speech changes that some people experience before a migraine headache sets in. The wave itself also appears to trigger the pain pathways responsible for the headache that follows.
Congenital Sucrase-Isomaltase Deficiency
CSID (sometimes shortened to CSD) is a rare inherited digestive disorder affecting roughly 1 in 5,000 people of European descent. It’s far more common in Indigenous populations of Greenland, Alaska, and Canada, where up to 1 in 20 people may be affected. People with this condition lack an enzyme needed to break down sucrose (table sugar) and certain starches. Symptoms, including watery diarrhea, bloating, gas, and abdominal cramps, typically appear when an infant starts eating solid foods containing sugar or starch such as fruits, juices, and grains. In severe cases, it can lead to poor growth and chronic malnutrition. Diagnosis involves either a breath test that measures gases produced by undigested sugar or a small intestinal biopsy to measure enzyme activity directly.