WHAT IS THE MEANING OF HUMAN IMMUNODEFICIENCY VIRUS INFECTION?
Table 1–1 presents the case definition for adult, adolescent, and children, respectively, for human immunodeficiency virus (HIV) infection.
WHAT ARE THE CAUSES OF HUMAN IMMUNODEFICIENCY VIRUS INFECTION?
Infection with HIV occurs through three primary modes: sexual, parenteral, and perinatal. Sexual intercourse, primarily anal and vaginal intercourse, is the most common vehicle for transmission. The highest risk appears to be from receptive anorectal intercourse at about 1.4 transmissions per 100 sexual acts. Condom use reduces the risk of transmission by approximately 80%. Individuals with genital ulcers or sexually transmitted diseases are at great risk for contracting HIV.
The risk of HIV transmission from sharing needles is approximately 0.67 per 100 episodes.
Healthcare workers have a small risk of occupationally acquiring HIV, mostly through accidental injury, most often percutaneous needlestick injury.
Perinatal infection, or vertical transmission, is the most common cause of pediatric HIV infection. The risk of mother-to-child transmission is ~25% in the absence of antiretroviral therapy. Breastfeeding can also transmit HIV.
WHAT ARE THE SIGNS AND SYMPTOMS OF HUMAN IMMUNODEFICIENCY VIRUS INFECTION?
Clinical presentations of primary HIV infection vary, but patients often have a viral syndrome or mononucleosis-like illness with fever, pharyngitis, and adenopathy (Table 1–2). Symptoms may last for 2 weeks.
Most children born with HIV are asymptomatic. On physical examination, they often present with unexplained physical signs such as lymphadenopathy, hepatomegaly, splenomegaly, failure to thrive, weight loss or unexplained low birth weight, and fever of unknown origin. Laboratory findings include anaemia, hypergammaglobulinemia, altered mononuclear cell function, and altered T-cell subset ratios. The normal range for CD4 cell counts in children is much different than for adults.
Clinical presentations of the opportunistic infections are presented in Infectious Complications of HIV below.
The probability of progression to AIDS is related to RNA viral load; the viral load is a major prognostic factor for disease progression, CD4 count decline, and death.
The presence of HIV infection is screened with an enzyme-linked immunosorbent assay (ELISA), which detects antibodies against HIV-1. Positive screening tests are confirmed with another enzyme immunoassay to specify if the antibodies are to HIV-1 versus HIV-2. Rare false-positive results can occur, particularly in those with autoimmune disorders. False- negative results also occur and may be attributed to the “window period” before adequate production of antibodies or antigen.
Once diagnosed, HIV disease is monitored primarily by two surrogate biomarkers, viral load and CD4 cell count. The viral load test quantifies viremia by measuring the amount of viral RNA. There are several methods used for determining the amount of HIV RNA: reverse transcriptase-coupled polymerase chain reaction, branched DNA, transcription-mediated amplification, and nucleic acid sequence–based assay.
The number of CD4 lymphocytes in the blood is a surrogate marker of disease progression. The normal adult CD4 lymphocyte count ranges between 500 and 1600 cells/mm3 (500 and 1600 × 106/L), or 40% to 70% of all lymphocytes.
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