Table of Contents

Skye McGregor : Kirby Institute

Last reviewed: March 2019

In Australia, the epidemiology of human immunodeficiency virus (HIV) infection is monitored through a range of public health surveillance systems including case reporting, behavioural and biological surveys, and clinical data collection.

Case Reporting

Case reporting involves reporting of newly diagnosed HIV infection by state and territory health authorities to the Kirby Institute.^[1], ^[2] The notification includes a number of demographic and clinical characteristics, including sex, date of birth, date of diagnosis, CD4+ T  cell count at diagnosis, source of exposure to HIV, and clinical evidence of newly acquired infection.^[3]More recently, information has also been collected on country of birth, year of arrival in Australia, and language spoken at home. Exposure risk is based on self-reported information, and includes sexual exposure, history of injecting drug use, and the receipt of blood products or tissue. The exposure data are used to classify people into the following exposure categories, using a risk hierarchy: men who have sex with men; men who have sex with men and injecting drug use; injecting drug use; heterosexual contact; haemophilia/coagulation disorder; receipt of blood/tissue; mother with/at risk of HIV infection; and health care setting.^[4]Case-reporting of HIV infection in Australia also routinely distinguishes recently acquired HIV infections by collecting any available information on prior HIV testing or symptoms

characteristic of primary HIV infection (sometimes referred to as seroconversion illness) in the person diagnosed. Newly acquired HIV infection is defined as a newly diagnosed HIV infection with a negative or indeterminate HIV antibody test result in the last 12 months, or a diagnosis of primary HIV infection within 1 year of HIV diagnosis. Primary HIV infection is the period immediately following infection with HIV, and before an immune response reduces an individual’s HIV viral load. Symptoms of HIV infection usually present about 10 days after infection, and include a rash, myalgia, pharyngitis and headaches.^[5]

Morbidity associated with HIV infection is also monitored. If HIV infection is untreated, it usually progresses to acquired immune deficiency syndrome (AIDS) 8 to 10 years after initial diagnosis.^[6] In Australia, AIDS is defined as a definitive diagnosis of HIV infection and evidence of a defined opportunistic infection or clinical condition as outlined in Clinical Manifestations of HIV Disease.^[7] Due to high treatment coverage in Australia, in recent years the focus has shifted from reporting AIDS and AIDS-related deaths, to monitoring late and advanced diagnoses. A late diagnosis is indicated by a CD4+ T cell count < 350/µL and suggests HIV infection was acquired around 4-5 years earlier, with a mean decline in CD4+ T cell count per year of around 50-100/µL.^[8] Advanced HIV infection is considered to be present when the CD4+ T cell count falls below 200/µL, and the person is vulnerable to opportunistic infections characteristic of AIDS. Timely diagnosis of HIV infection can reduce an individual’s risk of morbidity and mortality, and has public health benefits by providing opportunities to reduce onward transmission, through mitigation of risk-behaviours or commencing treatment to reduce infectivity.

Other surveillance systems

Routine case reporting is supplemented by enhanced surveillance activities in Australia, including a network of sentinel surveillance sites and biological and behavioural surveys. The network of sentinel surveillance sites (called ACCESS) includes sexual health clinics, primary health care clinics, Aboriginal Medical Services and laboratories, and provides information on routine HIV testing and positivity. Repeat surveys provide valuable information on trends over time in risk behaviours and infection. In high-risk populations these surveys include the Gay Community Periodic Survey^[9] and the Australian Needle and Syringe Program Survey.^[10] Surveys in the general population include the Australian Study of Health and Relationships^[11] and the National Survey of Secondary Students and Sexual Health.^[12]