HIV-infected patients are susceptible to other infections because the virus itself damages the body's ability to ward off invasion by other germs, even those that are too weak to infect healthy people. These secondary infections by weak germs are known as opportunistic infections. One of the most common opportunistic infections is caused by an organism known as Mycobacterium avium complex (MAC). Effective therapy for HIV infection (which consists of combinations of medications known as highly active antiretroviral therapy [HAART]) partially restores the body's ability to ward off opportunistic infections and has greatly improved the outcome of these infections. As a result of HAART's ability to improve resistance to infection among HIV-infected patients, the U.S. Public Health Service and the Infectious Diseases Society of America have recommended that treatment (or preventive therapy) for most opportunistic infections can be stopped after successful treatment with HAART. On the other hand, they have recommended that treatment for MAC infection be continued indefinitely, no matter how effective the previous response to HAART. Despite this recommendation, some doctors have stopped treatment for MAC infection after the patient has had a good response to HAART.