skip navigation

Skip Nav

Education Materials

Education Materials

AIDSinfo Glossary Search

A - Z Index


Salmonella Audio (En español)

A group of bacteria. Salmonella is the most common cause of foodborne illnesses in the United States. Infection with Salmonella can cause diarrhea, nausea, fever, and headache. In people with weakened immune systems, including people with HIV, the symptoms of Salmonella infection are more severe than in people with healthy immune systems.

Salmonella Septicemia Audio (En español)

A life-threatening Salmonella infection that has spread to the bloodstream. Salmonella septicemia can be caused by any of the Salmonella bacteria, which are found in contaminated food and water. The infection is systemic and affects virtually every organ system. The most common symptom is a fever that comes and goes. In people with HIV, recurrent Salmonella septicemia is an AIDS-defining condition.

See Related Term(s): AIDS-Defining Condition, Salmonella

Salvage Therapy Audio (En español)

Also known as: Rescue Therapy

Therapy given when the standard treatment for a disease or condition is no longer effective and when treatment options are limited. HIV salvage therapy is designed for people with treatment failure on more than one HIV treatment regimen and with extensive HIV drug resistance.

See Related Term(s): Drug Resistance, Treatment Failure

San Joaquin Valley Fever

Also known as: Coccidioidomycosis


Also known as: Subcutaneous Adipose Tissue


Also known as: Self-Administered Therapy


Also known as: Subcutaneous

Seborrheic Dermatitis Audio (En español)

A non-contagious inflammatory skin condition characterized by flaky, white to yellowish scales on various areas of the body, including the scalp, eyebrows, eyelids, ears, and trunk. Seborrheic dermatitis can occur with or without redness. The exact cause of seborrheic dermatitis is unknown, but it may be due to an overproduction of skin oil combined with irritation from a yeast. Factors that might increase the risk of seborrheic dermatitis include family history, stress, fatigue, use of alcohol-containing lotions, skin disorders, obesity, HIV infection, and certain neurologic conditions.

Secondary Prophylaxis

Also known as: Maintenance Therapy

Secondary Resistance

Also known as: Acquired Resistance

Self-Administered Therapy (SAT) Audio (En español)

A method of drug administration in which a person takes medication without being observed by a health care professional.

See Related Term(s): Directly Observed Therapy

Semen Audio (En español)

Also known as: Seminal Fluid

A thick, whitish fluid that is discharged from the male penis during ejaculation. Semen contains sperms and various secretions. HIV can be transmitted through the semen of a man with HIV.

Semen-Derived Enhancer of Virus Infection (SEVI) Audio (En español)

Protein fibers found in semen that can trap HIV and help HIV attach to cells. Semen-derived enhancer of virus infection (SEVI) increases the risk of sexual transmission of HIV.

Seminal Fluid

Also known as: Semen

Sensitivity Audio (En español)

The probability that a medical test will detect the condition being tested for in people who actually have the condition. In other words, a sensitive test is one that produces true positive results. For example, the enzyme-linked immunosorbent assay (ELISA) HIV antibody test is highly sensitive, which means the test can detect HIV in most people infected with HIV. However, because the ELISA can sometimes mistakenly recognize antibodies to other diseases as antibodies to HIV (a false positive result), a Western Blot or other HIV test is used to confirm a positive ELISA HIV antibody test.

See Related Term(s): Specificity, True Positive

Sepsis Audio (En español)

An overwhelming, life-threatening immune response to infection. Sepsis causes a systemic reaction that includes fever, chills, rapid heart rate, increased breathing rate, and possibly shock. Sepsis can also cause body organs, such as the kidneys or lungs, to fail. Sepsis is more likely to occur in people with weakened immune systems, including people with HIV, than in people with healthy immune systems.

Seroconversion Audio (En español)

When an HIV-infected person converts from HIV negative to HIV positive by blood testing. Shortly after infection with HIV, the body begins to produce HIV antibodies. It takes the body a while to produce enough antibodies to be detected by an HIV antibody test—usually 10 to 14 days but sometimes up to 6 months. When HIV antibodies in the blood reach a detectable level, the HIV-infected person seroconverts. In other words, the person’s antibody test goes from HIV negative to HIV positive.

See Related Term(s): Window Period

Serologic Test Audio (En español)

A blood test to detect the presence of antibodies against a microorganism. A serologic test can determine whether a person has been exposed to a particular microorganism.

Seroprevalence Audio (En español)

The overall occurrence of a disease or condition within a defined population at one time, as measured by blood tests (serologic tests).

Serostatus Audio (En español)

The state of either having or not having detectable antibodies against a specific antigen, as measured by a blood test (serologic test). For example, HIV seropositive means that a person has detectable antibodies to HIV; seronegative means that a person does not have detectable HIV antibodies.

Serum Audio (En español)

The clear, yellowish liquid part of blood that remains after clotting. Serum is used for various laboratory tests.

Serum Glutamate Pyruvate Transaminase

Also known as: Alanine Aminotransferase

Serum Glutamic-Oxaloacetic Transaminase

Also known as: Aspartate Aminotransferase

Set Point Audio (En español)

Also known as: Viral Set Point

The viral load (HIV RNA) that the body settles at within a few weeks to months after infection with HIV. Immediately after infection, HIV multiplies rapidly and a person’s viral load is typically very high. After a few weeks to months, this rapid replication of HIV declines and the person's viral load drops to its set point.

See Related Term(s): Viral Load

Sexual Transmission Audio (En español)

Transmission of HIV, or other sexually transmitted infection, from one individual to another as the result of sexual contact.

See Related Term(s): Vertical Transmission

Sexually Transmitted Disease

Also known as: Sexually Transmitted Infection

Sexually Transmitted Infection (STI) Audio (En español)

Also known as: Sexually Transmitted Disease

An infectious disease that spreads from person to person during sexual contact. Sexually transmitted infections, such as syphilis, HIV infection, and gonorrhea, are caused by bacteria, parasites, and viruses.


Also known as: Placebo

Shigellosis Audio (En español)

An enteric (intestinal) infection caused by the bacterium Shigella, which is typically transmitted through contact with contaminated human feces. Symptoms usually include watery or bloody diarrhea, abdominal pain, nausea, and fever. Certain bacterial enteric infections, including shigellosis, occur at a much higher rate in people with HIV than in people with healthy immune systems.

See Related Term(s): Opportunistic Infection

Shingles Audio (En español)

A non-contagious disease caused by the varicella zoster virus (VZV or HHV-3). VZV is the same virus that causes chickenpox. The virus remains in the nervous system of people who have had chickenpox, and it can become active years later to cause shingles. Symptoms of shingles can include numbness, itching, and severe pain that is followed by a rash of blister-like lesions along one side of the body. The pain can persist for weeks, months, or years after the rash heals. People with HIV are more at risk for shingles than people with healthy immune systems.

See Related Term(s): Herpesviruses, Varicella Zoster Virus

Simian Immunodeficiency Virus (SIV) Audio (En español)

An HIV-like virus that can infect monkeys and apes and can cause a disease similar to AIDS. Because HIV and simian immunodeficiency virus (SIV) are closely related viruses, researchers study SIV as a way to learn more about HIV. However, SIV cannot infect humans, and HIV cannot infect monkeys.

See Related Term(s): Human Immunodeficiency Virus

Single-Blind Study Audio (En español)

Also known as: Single-Masked Study

A type of clinical trial in which either the investigators or the participants are unaware of the treatment that the participants are receiving.

See Related Term(s): Clinical Trial, Double-Blind Study

Single-Masked Study

Also known as: Single-Blind Study


Also known as: Simian Immunodeficiency Virus


Also known as: Stevens-Johnson Syndrome

South American Trypanosomiasis

Also known as: Chagas Disease

Specificity Audio (En español)

The probability that a medical test will correctly produce a negative test result for a person who does not have the condition being tested. In other words, a specific test is one that produces true negative results. For example, the specificity of the Western Blot is very high; the test seldom mistakes antibodies to other diseases as antibodies to HIV. For that reason, the Western Blot is used to confirm a positive enzyme-linked immunosorbent assay (ELISA) or other HIV antibody test.

See Related Term(s): Sensitivity, True Negative

Spermicide Audio (En español)

A topical preparation or substance used during sexual intercourse to kill sperm. Although spermicides may prevent pregnancy, they do not protect against HIV infection or other sexually transmitted infections. Irritation of the vagina and rectum that sometimes occurs with use of spermicides may increase the risk of sexual transmission of HIV.

Sperm Washing Audio (En español)

A laboratory procedure that involves “washing” semen from an HIV-infected man to separate the sperm from the fluid part of the semen. Because the seminal fluid contains the highest concentration of HIV, the “washed” sperm should not contain any HIV. Sperm washing can be considered as a reproductive option for an HIV discordant couple in which the man is the HIV-infected partner. Because sperm washing has not been proven completely effective, couples using the procedure should be counseled regarding the potential risks for transmission of HIV.

See Related Term(s): Discordant Couple

Spinal Tap Audio (En español)

Also known as: Lumbar Puncture

A procedure in which a needle is inserted into the lower region of the spinal cord to collect cerebrospinal fluid (CSF). The CSF is examined in a laboratory to diagnose and monitor certain infections. A spinal tap may also be performed to inject drugs or to reduce spinal fluid pressure.

See Related Term(s): Cerebrospinal Fluid

Spleen Audio (En español)

An organ of the lymphatic system. The spleen is located on the left side of the body, above the stomach. The spleen helps fight infection, keeps body fluids in balance, stores blood, and destroys old and damaged cells.

See Related Term(s): Lymphatic System

Splenomegaly Audio (En español)

Abnormal enlargement of the spleen.

See Related Term(s): Spleen

Sputum Analysis Audio (En español)

Laboratory evaluation of sputum to detect certain infections, such as bacterial pneumonia and tuberculosis (TB). Sputum is the mucus-containing material produced by the cells lining the lungs and airways (bronchial tubes). The sputum used for analysis is collected when a person coughs or spits.

Standard of Care Audio (En español)

Treatment that experts agree is appropriate, accepted, and widely used for a given disease or condition.

Statin Audio (En español)

Also known as: HMG-CoA Reductase Inhibitor, Lipid-Lowering Agent

A drug used to lower the amount of cholesterol and certain fats in the blood. Statins block a key liver enzyme involved in making cholesterol.

See Related Term(s): Cholesterol

Stem Cells Audio (En español)

Unspecialized cells from which other types of cells develop. When a stem cell divides, each new cell has the potential either to remain a stem cell or to become a specialized cell with a distinct function, such as a muscle cell or blood cell. Stem cells serve as a repair system for the body, replacing old and damaged cells. Research on using stem cells to treat various diseases is currently under way.

Stevens-Johnson Syndrome (SJS) Audio (En español)

A severe and sometimes fatal form of skin rash characterized by red, blistered spots on the skin; blisters in the mouth, eyes, genitals, or other moist areas of the body; peeling skin that results in painful sores; and fever, headache, and other flu-like symptoms. Internal organs may also be affected. Stevens-Johnson syndrome (SJS) may occur as a severe reaction to certain drugs, including some antiretroviral (ARV) HIV drugs.


Also known as: Sexually Transmitted Infection

Stomatitis Audio (En español)

Inflammation of the mucous membranes of the mouth, such as the gums or lips. The causes of stomatitis vary and can include injury to the mouth, allergy, and infection.

Strain Audio (En español)

A group of organisms, such as bacteria or viruses, that belong to the same species and share certain characteristics not found in other members of the species. For example, HIV can mutate into different strains, with each strain having a different type of resistance to antiretroviral (ARV) drugs.

Streptococcus Pneumonia Infection Audio (En español)

Infection caused by the bacterium Streptococcus pneumonia, which is spread through contact with respiratory droplets from a person who is infected with or carrying the bacteria. The bacteria are a major cause of common illnesses, such as inflammation of the sinuses (sinusitis), but can also result in life-threatening infections, including meningitis and pneumonia. People with weakened immune systems, including people with HIV, are at higher risk for bacterial pneumonia, including Streptococcus pneumonia infection, than people with healthy immune systems.

See Related Term(s): Opportunistic Infection, Pneumonia

Stroke Audio (En español)

Also known as: Brain Attack

An interruption of blood flow to the brain, caused by a broken or blocked blood vessel. A stroke results in sudden loss of brain function, such as loss of consciousness, paralysis, or changes in speech. Stroke is a medical emergency and can be life-threatening.

Structured Treatment Interruption (STI) Audio (En español)

Also known as: Drug Holiday

A planned break from treatment, during which a person stops taking medications. Structured treatment interruptions (STIs) may be used to reduce toxic effects of medications, to enhance a medication’s effectiveness when restarted, or as a step towards stopping treatment all together. Structured interruption of HIV treatment is not recommended outside of controlled clinical trials.

Subclinical Infection Audio (En español)

An infection that has no symptoms or noticeable signs. A subclinical infection may be an early stage of an infection or a very mild infection.

Subcutaneous (SC) Audio (En español)

Pertaining to the area beneath the layers of the skin. Some drugs are given by subcutaneous injection.

Subcutaneous Adipose Tissue (SAT) Audio (En español)

Fat tissue located right under the skin. HIV-associated lipodystrophy can include changes in subcutaneous adipose tissue (SAT) and may be related to use of certain antiretroviral (ARV) drugs.

See Related Term(s): Lipodystrophy, Visceral Adipose Tissue

Substance Abuse and Mental Health Services Administration (SAMHSA) Audio (En español)

The lead federal agency for reducing the impact of substance abuse and mental illness in the United States. The Substance Abuse and Mental Health Services Administration (SAMHSA) has a Web site that focuses specifically on behavioral health and HIV/AIDS.

Subtype Audio (En español)

Also known as: Clade

A subgroup of genetically related HIV-1 viruses. HIV-1 can be classified into four groups: M Group, N Group, O Group, and P Group. Viruses within each group can then be further classified by subtype. For example, the HIV-1 M group includes at least nine subtypes: A1, A2, B, C, D, F1, F2, G, H, J, and K.


Also known as: Glucose

Sugar Pill

Also known as: Placebo

Superinfection Audio (En español)

When a person who is already infected with HIV becomes infected with a second, different strain of HIV. Superinfection may cause HIV to advance more rapidly. Superinfection can also complicate treatment if the newly acquired strain of HIV is resistant to antiretroviral (ARV) drugs in the person’s current HIV treatment regimen.

See Related Term(s): Drug Resistance

Superiority Trial Audio (En español)

A clinical trial designed to show that a new drug (or other treatment) is more effective than the drug to which it is compared.

See Related Term(s): Non-Inferiority Trial

Supressor T Cell

Also known as: Regulatory T Lymphocyte

Supressor T Lymphocyte

Also known as: Regulatory T Lymphocyte

Surrogate Endpoint Audio (En español)

Also known as: Surrogate Marker

Substitute measure for a clinical endpoint. Because it can be difficult to measure clinical endpoints in studies running for several years, researchers often use surrogate endpoints as substitute measures for clinical endpoints. For example, in HIV-related clinical trials, rising CD4 count is used as a surrogate endpoint for progression of HIV infection.

See Related Term(s): Clinical Endpoint, Clinical Trial

Surrogate Marker

Also known as: Surrogate Endpoint

Sustained Viral Suppression

Also known as: Sustained Virologic Response

Sustained Virologic Response Audio (En español)

Also known as: Sustained Viral Suppression

The continuous, long-term suppression of a person’s viral load (HIV RNA)—generally to undetectable levels—as the result of treatment with antiretroviral (ARV) drugs.

Symptomatic HIV Infection Audio (En español)

Stage of HIV infection during which signs or symptoms of the infection begin to appear. The onset of symptoms signals the transition from asymptomatic HIV infection to full blown AIDS.

See Related Term(s): Acquired Immunodeficiency Syndrome, HIV Progression

Syncytium Audio (En español)

A large cell-like structure that forms when many cells fuse together. Syncytia can form during viral infection. In some people with HIV, syncytia formation has been linked to more rapid progression of HIV infection.

Syndrome Audio (En español)

A group of symptoms or conditions that occur together and are collectively associated with a specific disease or with the risk of developing a specific disease.

Syndrome X

Also known as: Metabolic Syndrome


Also known as: Drug Synergism


Also known as: Drug Synergism

Syphilis Audio (En español)

An infectious disease caused by the bacterium Treponema pallidum, which is typically transmitted through direct contact with a syphilis sore, usually during vaginal or oral sex. Syphilis can also be transmitted from an infected mother to her child during pregnancy. Syphilis sores occur mainly on the genitals, anus, and rectum, but also on the lips and mouth. Genital sores (chancres) caused by syphilis increase the risk of sexual transmission of HIV.

See Related Term(s): Opportunistic Infection, Sexually Transmitted Infection

Systemic Audio (En español)

Pertaining to the entire body. A systemic infection affects the whole body. Systemic drug therapy involves giving a drug that travels through the bloodstream and affects cells throughout the body.

Back to Top