18th June 2024

Clinical features

Seroconversion illness

Following exposure to HIV, patients undergo a latency period before symptoms manifest or a diagnosis can be readily made through conventional testing. Symptoms usually appear 2-4 weeks following infection and can occur as late as three months after. The HIV seroconversion illness typically consists of fevers, sore throat, rash and lymphadenitis.

Natural History of HIV Infection

The stages of HIV infection have been defined by the CDC. Following the Seroconversion illness (Stage 1), a patient enters an asymptomatic phase (Stage 2), lasting for usually 5 or even 10 or more years, although some variants are associated with a more-rapid progression. Stage 3, previously (and no longer) referred to as the Acquired Immunodeficiency Syndrome (AIDS), occurs when the absolute CD4+ T cell count falls below 200 cells per mm³. Without treatment, this stage of HIV typically has a life expectancy of 2-3 years.

Diagnosis

HIV-specific antibodies do not appear until at 2-12 weeks following infection, with >90% of patients being antibody positive at four weeks. Modern 4th generation ELISA testing can detect the p24 antigen as well as HIV1/2 antibody, conferring greater sensitivity in the early phases of the infection. Positive antibody testing is confirmed via western blot (also called immunoblot). Other methods, such as salivary testing for HIV antibody, and point-of-care 4ᵗʰ generation tests are also in common use, with comparable sensitivity and specificity.

Opportunistic Infections

A normal CD4+ count typically ranges from between 500 to 1,500 cells per mm³. The majority of opportunistic infections occur at CD4+ counts of 200 cells per mm³ or fewer. The various opportunistic pathogens associated with HIV are often grouped into the range of CD4+ count at which they are most expected to cause disease

< 200 cells per mm³: Pneumocystis jirovecii, oesophageal candidiasis

<100 cells per mm³ Cryptococcus neoformans, Toxoplasma gondii, Cryptosporidium parvum

<50 cells per mm³ Mycobacterium avium complex, cytomegalovirus