CDC Report of Cat-Scratch Disease in the United States

Each year about 12,500 people younger than 65 years of age are diagnosed with cat-scratch disease in the United States, according to a Centers for Disease Control and Prevention (CDC) study recently published in Emerging Infectious Diseases. The incidence of cat-scratch disease during the study period was highest in children 5 to 9 years of age. The CDC estimates the total annual medical cost for cat-scratch disease in United States to be $9.76 million.

“[Cat-scratch disease] causes a substantial burden of disease nationwide and disproportionately affects children,” write the authors. The disease is caused by the bacterium Bartonella henselae, which is spread among cats (the reservoir species) by fleas. Humans become infected via cat scratches and bites. A typical symptom in humans is lymphadenopathy near the site of a cat scratch; systemic disease can also occur.

The CDC analyzed data collected in a large medical insurance claims database from 2005 through 2013. The database included information from employer-sponsored health insurance claims for people under 65 years of age. The number of enrollees per year ranged from about 16 million to 53 million.

Over the 9-year study period, 13,273 patients (of over 280 million person-years analyzed) received a medical code for cat-scratch disease as a primary or secondary diagnosis. Of these, 12,735 were treated as outpatients and 538 were admitted to the hospital. The CDC calculated the average incidence per year to be 4.5 outpatients and 0.19 inpatients per 100,000 population.

Nearly one-third of the cat-scratch disease diagnoses were in children aged 14 years or younger. The incidence in children 5 to 9 years of age was 9.0 cases per 100,000 population. Women and girls received 62% of outpatient diagnoses and 55.6% of inpatient diagnoses.

More diagnoses were made in January than any other time of year, followed by August through November. The authors have no explanation for the January peak. They theorize that adoption of cats and kittens during the holidays or increased time spent indoors with cats during the winter school break could be responsible, but they note that no data are available to support these hypotheses.

Outpatient diagnoses of cat-scratch disease decreased over the study period, although hospital admissions remained relatively stable. The authors suggest that the decrease could be related to the development of more effective flea control products for cats or improved diagnostic capability for other causes of lymphadenopathy (resulting in fewer false diagnoses of cat-scratch disease). The overall incidence of hospital admissions in this analysis was lower than that reported in other studies. The authors note that the exclusion of patients 65 years and older from the database could have affected this calculation.

Study limitations listed by the authors relate to the nature of the database. Medical codes for cat-scratch disease could have been entered in error, and certain population segments are excluded. The authors also write that the calculated annual cost of cat-scratch disease could be an underestimate because it does not account for lost work time or medical visits that did not receive the appropriate code.

To reduce the risk for cat-scratch disease, the authors recommend controlling fleas in cats, practicing hand hygiene after handling cats, restricting cats from hunting outdoors, and educating cat owners.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.