Opportunistic Infections (OIs)

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Infections that develop if the immune system is severely damaged. OIs can occur in people without HIV, but can be more serious and severe for people with HIV if there is advanced immune deficiency, in the absence of effective HIV antiretroviral treatment. OIs are due to viruses, bacteria, protozoa and fungi that exist either normally within the body or commonly in the environment. They may be new infections that do not cause serious disease if the immune system is intact, or previously acquired infections that enter a latent period and are reactivated if the immune system is damaged. The risk of developing an OI is greater is the CD4 cell count is below 200, at which point other drug treatments are often used to prevent and treat these infections. However, taking HIV antiretroviral (ARV) treatment – which supresses the viral load to low levels, which in turn gives rise to gradual increases in the CD4 cell count restoring the immune system – is the best way to prevent OIs from occurring. OIs are rare if HIV ARV treatment is taken daily. Thus, for people taking effective HIV ARV treatment (with improved CD4 immune T cell counts), these OI conditions are highly unlikely to happen due to the immune reconstitution benefits of HIV ARV treatment. Without HIV antiretroviral treatment, OIs can occur and the CD4 count drops to very low levels, this is then called ‘AIDS (Acquired Immune Deficiency Syndrome)’ and the risk of death is also increased. Examples of AIDS Opportunistic Infections (OIs) are:  Cryptococcosis;, Cryptosporidiosis; Cytomegalovirus (CMV); Progressive Multifocal Leukoencepalopathy (PML); Non-Hodgkin’s Lymphoma(NHL); Karposi’s Sacoma (KS); Pneumocystis Jiroveci pneumonia (PJP); Mycobacterium Avium Complex (MAC); Toxoplasmosis; Microsporidiosis; Molluscum contagiosum. OIs can affect every body part, and can also affect the brain and lead to a condition called AIDS Dementia Complex (ADC). Treatment with HIV ARV therapy halts and reverses many OIs, including ADC.

Note: We have not defined many of these OIs in this guide because they are rare when effective HIV ARV treatment is taken daily.