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 2023,

Worldwide:

• 39.9 million [36.1 million–44.6 million] people globally were living with HIV 
• 1.3 million [1 million–1.7 million] people became newly infected with HIV
• 630 000 [500 000–820 000] people died from AIDS-related illnesses 
• 30.7 million people [27–31.9 million] were accessing antiretroviral therapy
• 88.4 million [71.3 million–112.8 million] people have become infected with HIV since the start of the epidemic. 
• 42.3 million [35.7 million–51.1 million] people have died from AIDS-related illnesses since the start of the epidemic

Asia and the Pacific region:

• 6.7 million people were living with HIV
• 13% decrease in new HIV infections since 2010
• 51% decrease in AIDS-related deaths since 2010
• 67% were on anti-retroviral therapy (ART)
• 300,000 newly infected cases were reported
• 150,000 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 11,641 cases of HIV infection were reported from 1984 to 2022 under the voluntary and anonymous HIV/AIDS reporting system.

409 new HIV infection cases were reported in 2022. 8.5% decrease compared to the 447cases in 2021. People infected with HIV progress to AIDS when they suffer from clinical complications of severe immunodeficiency due to HIV. In 2022, 62 AIDS reports were received.