ESSENTIALS OF DIAGNOSIS
Modes of transmission: sexual contact with an infected person, parenteral exposure to infected blood (transfusion or needle sharing), perinatal exposure.
Prominent systemic complaints: sweats, diarrhea, weight loss, and wasting.
Opportunistic infections due to diminished cellular immunity—often life-threatening.
Aggressive cancers, particularly non-Hodgkin lymphoma.
Neurologic manifestations, including dementia, aseptic meningitis, and neuropathy.
When AIDS was first recognized in the United States in 1981, cases were identified by finding severe opportunistic infections such as Pneumocystis pneumonia that indicated profound defects in cellular immunity in the absence of other causes of immunodeficiency. When HIV was identified as the cause of the syndrome, it became obvious that severe opportunistic infections and unusual neoplasms were at one end of a spectrum of disease, while healthy seropositive individuals were at the other end.
The Centers for Disease Control and Prevention (CDC) AIDS case definition (Table 31–1) includes opportunistic infections and malignancies that rarely occur in the absence of severe immunodeficiency (eg, Pneumocystis pneumonia, central nervous system lymphoma). It also classifies persons as having AIDS if they have positive HIV serology and certain infections and malignancies that can occur in immunocompetent hosts but that are more common among persons infected with HIV (pulmonary tuberculosis, invasive cervical cancer). Several nonspecific conditions, including dementia and wasting (documented weight loss)—in the presence of a positive HIV serology—are considered AIDS. The definition includes criteria for both definitive and presumptive diagnoses of certain infections and malignancies. Finally, persons with positive HIV serology who have ever had a CD4 lymphocyte count below 200 cells/mcL or a CD4 lymphocyte percentage below 14% are considered to have AIDS. Inclusion of persons with low CD4 counts as AIDS cases reflects the recognition that immunodeficiency is the defining characteristic of AIDS. The choice of a cutoff point at 200 cells/mcL is supported by several cohort studies showing that AIDS will develop within 3 years in over 80% of persons with counts below this level in the absence of effective antiretroviral therapy (ART). The prognosis of persons with HIV/AIDS has dramatically improved due to the development of effective ART. One consequence is that fewer persons with HIV ever develop an infection or malignancy or have a low enough CD4 count to classify them as having AIDS, which means that the CDC definition has become a less useful measure of the impact of HIV/AIDS in the United States. Conversely, persons in whom AIDS had been diagnosed based on a serious opportunistic infection, malignancy, or immunodeficiency may now be markedly healthier, with high CD4 counts, due to the use of ART. Therefore, the Social Security Administration as well as most social service agencies focus on functional assessment for determining eligibility for benefits rather than the simple presence or absence of an AIDS-defining illness.
Table 31–1.CDC AIDS case definition for surveillance of adults and adolescents.