Discuss the epidemiology and natural history of the acquired immunodeficiency syndrome (AIDS). (<250 words)

AIDS is caused by the human immunodeficiency virus (HIV), a retrovirus that contains only RNA and which must infect a host cell such as a CD4 lymphocyte or a macrophage in order to propagate. HIV is most often spread as a sexually transmitted disease. In the U.S., about 70% of AIDS cases are seen in homosexual/bisexual males. Another 5% result from heterosexual transmission. The second major means of spread of HIV in the U.S. is through contaminated needles with intravenous drug abuse, accounting for about 20% of AIDS cases. AIDS can also be acquired congenitally, either in utero or through breast milk, but only 1% of AIDS cases in the U.S. occur in this manner.

AIDS initially causes either a mononucleosis-like disease or, more often, no apparent disease. The HIV then becomes a latent infection in the host for years. During this time, the infected host is seropositive for HIV and can be detected only by laboratory testing, usually for antibody to HIV. After about 10 years, on average, the infected person begins to manifest such symptoms as lymphadenopathy, fever, and weight loss. This corresponds with a decrease in CD4 (helper) lymphocytes. When the CD4 count drops below 200, the infected person has a high probability of developing opportunistic infections and neoplasms. Though some of the complications of AIDS

Discuss how you would use clinical, laboratory, and pathologic findings to determine if a patient of yours has AIDS. (<250 words)

(Example 1)

Patients may present with an acute HIV infection with fever, sore throat, headache, skin rash, and lymphadenopathy soon after initial infection. These symptoms along with a history of a risk factor such as unprotected intercourse or intravenous drug use should suggest the need for HIV testing. A 6 week lag time between infection and seroconversion exists so that patients with recent exposure should be tested again. An initial negative test establishes a baseline for further assessment. Initial HIV testing is done with a highly sensitive and specific ELISA assay for antibody, and positives are further confirmed with a Western blot test. Clinical AIDS, however, will be be manifested for another 8 to 10 years, on average. Progression to AIDS is determined from a declining number of CD4 lymphocytes. A CD4 count less than 200/microliter in an HIV infected person is diagnostic for AIDS. Progression to AIDS is also marked by the appearance of opportunistic infect™ns such as Pneumocystis carinii (jirovecii), cytomegalovirus, fungal infections (especially Cryptococcus), cryptosporidium, and Toxoplasma gondii as well as neoplasms such as Kaposi's sarcoma and high-grade lymphomas. Additional laboratory findings seen with progression to AIDS include a reversed CD4/CD8 lymphocyte ratio, an increased beta-2-microglobulin, and increased serum or urine neopterin.

Discuss how you would use clinical, laboratory, and pathologic findings to determine if a patient of yours has AIDS. (<250 words)

(Example 2)

The history and physical examination are of great importance. A clinician must inquire about sexual practices and partners, intravenous drug use or other blood exposure, or possible congenital exposure, all of which are risks for HIV infection. Initial infection with HIV is associated with a mononucleosis-like syndrome. An ELISA antibody test for HIV is performed and, if positive, is confirmed with a Western blot test. If an infant is being tested, then a p24 antigen assay or viral culture must be used due to the presence of maternal antibody. Progression to AIDS is marked by the appearance of fever, chills, lymphadenopathy, and the presence of non-life threatening infections such as Herpes or Candida. The CD4/CD8 ratio reverses and the HIV viral titer rises. A staging system for HIV infection is based upon the CD4 lymphocyte count and the presence of certain opportunistic infections and neoplasms characteristic for AIDS. The numbers 1, 2, and 3 indicate CD4 counts of >500, 200 to 499, and <200/microliter respectively. The letters A, B, and C correspond to an asymptomatic state, infection with non-life threatening conditions, and infection with life-threatening diseases respectively. AIDS is diagnosed with a "3" or a "C" stage. Thus, AIDS is present in an HIV-infected person when either the CD4 count is <200/microliter or diseases such as Pneumocystis carinii (jirovecii) pneumonia, Toxoplasma encephalitis, Cryptococcal meningitis, cryptosporidial diarrhea, HIV encephalopathy, cytomegalovirus retinitis, or Kaposi's sarcoma of skin are present.