Seroconversion

  • Seroconversion is the period of time during which HIV antibodies develop and become detectable.
  • Seroconversion generally takes place within a few weeks of initial infection.
  • It is often, but not always, accompanied by flu-like symptoms including fever, rash, muscle aches and swollen lymph nodes. These symptoms are not a reliable way to identify seroconversion or to diagnose HIV infection.

Seroconversion is the interval, several weeks after HIV infection, during which antibodies are first produced and rise to detectable levels. Antibodies generally begin to appear within one to two weeks of exposure, and antibody concentrations (titres) continue to increase for several months thereafter. Seroconversion takes place within three weeks in most infected individuals, although very rare cases are reported in which seroconversion does not occur for up to a year.1

Seroconversion is often – although not always – accompanied by a flare of symptoms called seroconversion illness (sometimes also called acute retroviral syndrome). Symptomatic seroconversion illness occurs in at least 50%, and possibly as many as 80 or 90%, of infected individuals.

When symptoms are present, they are usually 'flu-like' in nature, typically including any one or more of: fever, rash, swollen lymph nodes, muscle aches and joint pains. Less commonly, symptoms may also include headache, sore throat, diarrhoea or other gastrointestinal upsets, ulcers of the oesophagus, anus and/or vagina, oral candidiasis, and central nervous system disorders including encephalitis and meningitis. There are often abnormalities in laboratory values during seroconversion, including increased levels of inflammatory cytokines (indicating immune activation) and a short-term decrease in lymphocytes (white blood cells), followed by an increase in CD8+ cells and overall lymphocytes.

These symptoms typically begin one to four weeks after infection and almost always resolve within two to three weeks, although the swollen lymph nodes, tiredness and malaise can persist much longer. Since most symptoms are so non-specific (except for the reddish, macular (small, flat blemishes), non-itchy rash, which may provide a distinctive sign for an experienced clinician), and may not be present at all, they may easily be missed or misattributed to a flu or other viral infection.

At this stage, people are extremely infectious, and this issue is dealt with in a previous section.

The interval after infection, but prior to seroconversion, is called the window period. 2 3

References

  1. Morpeth SC et al. Time to HIV-1 seroconversion similar among patients with acute HIV-1 infection; but there are exceptions… Thirteenth Conference on Retroviruses and Opportunistic Infections, Denver, poster 389, 2006
  2. Pillay D and Fisher M Primary HIV infection, phylogenetics, and antiretroviral prevention. J Infect Dis 195: 924-26, 2007
  3. Levy JA HIV and the pathogenesis of AIDS, Third edition. Washington: ASM Press, 2007
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