Even if a person tests negative to HIV antibody tests, he or she may still be within the window period; if infected, that person’s immune system has not yet begun making a detectable amount of antibodies against the virus. A person in the window period will test positive for HIV only if a virological test is used

AIDS is an acronym for “Acquired Immune Deficiency Syndrome”. It is the advanced stage of HIV infection.

The human immunodeficiency virus (HIV) is an agent or just infection that leads to the complication - AIDS in humans. Researchers have identified two types of HIV: HIV-1 and HIV-2. HIV-1 and HIV-2 are transmitted in the same way and are associated with similar opportunistic infections, though they differ in the efficiency of transmission and rates of disease progression.

The diagnosis of an HIV infection is most often based on the detection of antibodies to the virus. An antibody test is rarely 100% sensitive (correctly able to categorise an infected person as positive) and 100% specific (correctly able to categorise a non-infected person as negative). The World Health Organisation recommends that all positive test results be confirmed by re-testing, preferably using a different testing method.

HIV infects a person’s CD4 and T-cells and uses them to make copies of them–a process known as replication. In a person infected with HIV, CD4 cells are progressively destroyed.

When this happens, an infected person’s immune system is weakened, and the person is more likely to develop opportunistic infections and certain cancers. Any other infection that stimulates the immune system is likely to accelerate this destruction.

HIV is found in blood, genital fluid (semen, vaginal fluids,) cerebrospinal fluid, amniotic fluid, ascitic fluid and breast milk. It can be transmitted in any of three ways: through unprotected and unsafe sexual contact with an infected person; blood and blood products; and from infected mother to baby before or during birth or through breast-feeding afterbirth.

The chance that a person will become infected with HIV varies greatly depending on the type of exposure he or she has had. For example, the risk of becoming infected with HIV through a blood transfusion with infected blood is very high compared with the risk of becoming infected from an accidental needle prick in a health-care setting. Similarly, there is less risk of acquiring HIV from unprotected oral sex than from unprotected sex.

In order to reduce the risk, there is a need to understand that different behaviours carry different levels of risk.

About 70-80% of global HIV transmission occurs through unprotected sexual intercourse between infected persons and their partners. The sexual contact may be heterosexual or homosexual. Heterosexual vaginal intercourse is the predominant mode of transmission in many developing countries, including Nepal. While the probability of transmitting HIV in a single sexual act is quite low, even a lower-risk activity can get people infected if it is done many times.

Furthermore, the risk of infection can increase dramatically because of several factors, including the presence of a prior STI and unprotected intercourse with sexual partners.

HIV infections resulting from the transfer of infected blood account for about 5-10% of all HIV infections.

Transmission can occur through transfusion with contaminated blood or blood products and organ transplants from infected donors, so screening of donor is required. Additionally, HIV can be transmitted through direct contact with instruments that have been contaminated with infected blood and not sterilised before reuse in dental procedure, circumcision and tattooing.

A mother can transmit HIV to her child during pregnancy or delivery or through breastfeeding. The rates of HIV-1 transmission from mother to child range from 25- 40% in less-developed countries and from 15- 25% in more-developed countries.

During pregnancy, labour and delivery, the mother’s health, adherence to ART disruption of the placental barrier, preterm delivery and hemorrhage are significant predictors of the child’s infection. Viral, bacterial or parasitic placental infections are other factors that increase the opportunity for transmission during this period.

Most infants who acquire HIV during delivery are thought to have acquired it from maternal blood or cervical secretions that contain the virus.

After delivery, new born babies are provided ARV prophylaxis to decrease the risk of acquiring HIV. Another important thing is breast-feeding. The risk of transmitting HIV for children below 6 months of age through mix feeding increases, so it is advised to provide exclusive breastfeeding for initial six months of age.

For an HIV-infected individual, the window period is a common term used for the time between the initial HIV infection and the development of a measurable immunologic response to the infection. During this period, a person infected with HIV could still have a negative HIV test result.

Within this time frame, however, HIV is replicating in the blood and lymph nodes. The window period varies from person to person and can range from as little as two weeks to as long as three months.

Even if a person tests negative to HIV antibody tests, he or she may still be within the window period; if infected, that person’s immune system has not yet begun making a detectable amount of antibodies against the virus. A person in the window period will test positive for HIV only if a virological test is used. In Nepal, PCR based tests are available.

TNA PCR is used to diagnose HIV in babies under 18 months of age, and RNA PCR is used to monitor the response to therapy. However, virological testing is often not available or affordable.

Post-test counseling should, therefore, be optimised to detect persons who may have an HIV infection.

Lastly, remember that HIV infection has become a manageable chronic health condition, enabling people living with HIV to lead long and healthy lives.

Dr Budhathoky is chief of Eye, ENT and Oral Health, Dept of Health Service