Human Immunodeficiency Virus (HIV) and HIV Infection Stage

Human immunodeficiency virus (HIV)

The life cycle of the human immunodeficiency virus (HIV) is a complex 7-step process which involves invasion and destruction of the CD4 cells (a type of white blood cells that forms the body’s natural defense system), therefore destroying the immune system as the virus replicates. There are two types of HIV virus

  • HIV-1, which accounts for almost all HIV infection worldwide, and 
  • HIV-2, which is mostly confined to west Africa, is less infectious and is associated with slower decline in CD4 cells and progression of disease.

There are 3 stages of HIV infection, acute HIV infection, chronic HIV infection and AIDS.

Acute HIV infection - Stage 1 

During acute HIV infection, which is defined by the period between the presence of HIV RNA and detectable antibodies level (REF1), the HIV virus multiplies rapidly and is found in high concentration in the blood and bodily fluids for about 10-12 weeks (REF2). It has been reported that patients during the acute HIV infection state is 26 times more infectious than those during chronic HIV infection. It is suggested to get HIV test and start the HIV treatment. Approximately 10-50% of new HIV infections is believed to occur during the acute infection period, especially in relationships involving multiple or frequent change of sexual partner (REF3).

Chronic HIV infection - Stage 2

After the symptoms subsided, patients can remain asymptomatic but infectious for years while the virus continues to multiply at low levels. Without treatment, most patients will progress to AIDS.

AIDS - Stage 3

AIDS (acquired immunodeficiency syndrome) is the final stage of HIV infection, which is characterized by low CD4 count (less than 200 cells/mm3), as a result of prolonged untreated HIV infection, or the development of opportunistic infections (infections that usually pose little to no harm in healthy individuals) (REF4). Patients with AIDS have a high viral load and are very infectious.

Prevalence of HIV infection

According to UNAIDS, in 2019,


  • 38 million people worldwide were infected with HIV
  • 81% were aware of their HIV status,
  • 67% were on anti-retroviral therapy (ART)
  • 59% achieved undetectable viral load
  • 7.1 million people did not know they were infected with HIV
  • 1.7 million newly infected cases were reported
  • 690,000 deaths were reported due to AIDS-related illnesses

Asia and the Pacific region:

  • 5.8 million people were living with HIV
  • 75% were aware of their HIV status
  • 60% were on anti-retroviral therapy (ART)
  • 55% achieved undetectable viral load
  • 1.45 million people did not know they were infected with HIV
  • 300,000 newly infected cases were reported
  • 160,000 deaths were reported due to AIDS-related illnesses

HIV Infection - New Cases in HK

In Hong Kong, according to the Department of Health, a cumulative total of 10,785 cases of HIV infection were reported from 1984 to 2020 under the voluntary and anonymous HIV/AIDS reporting system.

505 new HIV infection cases were reported in 2020. An increasing trend of HIV infection among MSM was reported since 2004, and accounts for the majority of newly infected cases (272 out of 505 cases, 53.9%) in 2020.



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