I did a presentation at a conference last week with a physician on the topic of "Pets and Immunocompromised Owners". It led to some interesting discussion.  People with suboptimal immune systems are becoming more common in households and they often own pets. These individuals are susceptible to infections caused by microorganisms that would not typically cause disease in healthy people, and they are also more susceptible to severe (including fatal) disease caused by microorganisms that would only otherwise cause mild disease. Therefore, there’s a lot of concern about pets transmitting infection to immunocompromised people. Rarely is removal of pets from households of immunocompromised people necessary, but precautions should be taken to reduce the risks of disease transmission.

One topic that comes up periodically is testing for Bartonella henselae. This bacterium is the cause of cat scratch disease, which is spread by cats through scratches (obviously) but also through bites and by fleas. Cats that carry Bartonella henselae hardly ever have any signs of disease. In healthy people, cat scratch disease typically causes fever, local lymph node swelling, headache and fatigue.  Immunocompromised people, particularly people with HIV/AIDS, are at higher risk for severe disease, which can be fatal if it is not identified and treated promptly.  Similar disease can also be caused by other species of Bartonella that are not carried by cats.

Tests for Bartonella are not 100% accurate. Some tests just indicate exposure which does not tell you whether the cat is still carrying Bartonella or if it was previously exposed but already eliminated the bacterium from its body. False negative tests (e.g. the cat has been exposed but the test comes back negative anyway) can also occur. When considering screening tests, or any diagnostic tests in general, only do a test if there’s a reasonable chance that the results will affect what you do.

  • If a cat is positive, I wouldn’t recommend removing it from the house. It may or may not be shedding Bartonella, so the key points for avoiding cat scratch disease are reducing the risk of bites and scratches, and controlling fleas.
  • If a cat is negative, it’s probably (but not guaranteed to be) free of Bartonella, but it could be infected later in life, and the key points for avoiding cat scratch disease are reducing the risk of bites and scratches, and controlling fleas.

So, if the recommendations are exactly the same in both cases, save your money and spare the cat the blood sample.  I don’t recommend testing for Bartonella henselae.  The Infectious Disease Society of America also does not recommend testing (or treating) cats for Bartonella in their guidelines for HIV/AIDS patients.