Natural history of HIV infection

Mark Kelly1, Rajesh Varma2 

  1. Armidale Rural and Referral Hospital, Armidale, NSW
  2. Sydney Sexual Health Centre, Sydney NSW

Introduction

People with HIV infection rarely traverse the full natural history of HIV disease in Australia because the great majority of them are now commenced on antiretroviral therapy (ART) shortly after diagnosis. However, knowledge of the natural history of HIV infection is important for understanding strategies for the prevention of HIV infection and disease.

Transmission of HIV infection

Human immunodeficiency virus (HIV) is transmitted following contact with infected bodily fluids. The typical routes of transmission are unprotected sex, blood-to-blood contact (including sharing injecting equipment and, much less commonly, needle-stick injuries and receipt of contaminated blood products) and vertical transmission (from mother to child before, during and after birth). Less common routes include tattooing, organ and tissue transplantation, artificial insemination and invasive medical procedures.  The most common mode of HIV transmission is sexual transmission at the anogenital mucosa, accounting for 75-85% of cases worldwide. The probability of HIV transmission per episode of exposure varies (Figure 1). The risk of transmission per exposure may be influenced by factors such as co-existent genital ulcer disease, type of sexual act, vaginal flora, age, genetic factors and stage of HIV disease of the index case.[1]  There is a particularly high risk of transmission from someone with acute HIV infection; it has been estimated that transmission from a person with acute HIV infection accounts for more than 34-50% of cases of newly-acquired HIV infection.[2]