infections
Human Immunodeficiency Virus (HIV) Infection
Transmission of HIV Infection
The transmission of HIV requires contact of an open surface (such as a cut) in an uninfected person with a body fluid that contains the virus or cells infected with the virus. HIV can appear in nearly any body fluid, but transmission occurs mainly through blood, semen, vaginal fluid, and breast milk. Although tears, urine, and saliva may contain low concentrations of HIV, transmission through these fluids is extremely rare, if it occurs at all. HIV isnottransmitted by contact that does not involve exchange of body fluids (such as touching, holding, or dry kissing) or by close, nonsexual contact (such as touching a surface or an object). No case of HIV transmission has been traced to the coughing or sneezing of an infected person or to a mosquito bite. Transmission from an infected doctor or dentist to a patient is extremely rare. HIV is usually transmitted in the following ways: Sexual contact with an infected person, when the mucous membrane lining the mouth, vagina, penis, or rectum is exposed to body fluids such as semen or vaginal fluids that contain HIV, as occurs during unprotected sexual intercourse Injection of contaminated blood, as can occur when needles are shared or a health care worker is accidentally pricked with an HIV-contaminated needle Transfer from an infected mother to a child before birth, during birth, or after birth through the mother’s milk Medical procedures, such as transfusion of blood that contains HIV, procedures done with inadequately sterilized instruments, or Overview of Transplantation of an infected organ or tissues HIV is more likely to be transmitted if skin or a mucous membrane is torn or damaged—even if minimally. During vaginal or anal sex, small cuts may occur in the genitals or surrounding skin, even if the person is not aware that a cut is present. Most HIV infections are transmitted through heterosexual contact, but risk factors vary according to region. For instance, transmission among men who have sex with men is usually the most common way infection occurs in high-resource countries, but people who inject drugs are disproportionally affected in Southern Asia. In areas where heterosexual transmission is dominant, HIV infection follows routes of trade, transportation, and economic migration to cities and spreads secondarily to rural areas. Transmission of HIV through its most common routes—sexual contact or sharing of needles—is almost completely Prevention . No instance of HIV transmission through coughing, sneezing, or a mosquito bite has been documented. Risk of transmitting HIV is highest during vaginal or anal sex when a condom is not used or is used incorrectly. HIV transmission can also occur during oral sex, although transmission is less likely than during vaginal or anal sex. Risk of HIV infection is increased when semen or vaginal fluids contain a large amount of HIV and/or when there are tears or sores, even small ones, in the skin or membranes lining the genitals, mouth, or rectum. Thus, transmission is much more likely during the following: The first weeks after people are infected because at that time, the blood and body fluids contain very large amounts of HIV Vigorous sexual activities that damage the skin or membranes lining the genitals, mouth, or rectum Sexual intercourse when either partner has a genital herpes infection, syphilis, or another Overview of Sexually Transmitted Infections (STIs) (STI) that can cause sores or tears in the skin or inflammation of the genitals HIV (antiretroviral) medications can reduce the amount of HIV in semen and vaginal fluids. Thus, treatment of HIV infection with these medications can significantly reduce the likelihood of transmission. Sexual activities that can damage the membranes lining the genitals, mouth, or rectum include fisting (inserting most or all of the hand into the rectum or vagina) and using sex toys. Studies show that people with HIV infection who are treated with antiretroviral therapy and have an undetectable viral load (virally suppressed) do not sexually transmit the virus to their partners. Health care workers who are accidentally pricked with an HIV-contaminated needle have approximately a 1 in 300 chance of contracting HIV unless they are treated as soon as possible after exposure. Such treatment reduces the chance of infection to less than 1 in 1,500. The risk increases if the needle penetrates deeply or if the needle is hollow and contains HIV-contaminated blood (as with a needle used to draw blood or to inject street drugs) rather than simply being coated with blood (as with a needle used to stitch a cut). Infected fluid splashing into the mouth or eyes has less than a 1 in 1,000 chance of causing infection. HIV infection in a large number of women of childbearing age has led to an increase in Human Immunodeficiency Virus (HIV) Infection in Children and Adolescents . HIV infection can be transmitted from a mother infected with HIV to her child in the following ways: During pregnancy, to the fetus through the placenta During childbirth, to the baby during passage through the birth canal To the baby after birth through breast milk The overall cumulative risk of transmission from mother to child without antiretroviral medications is 35 to 45%. Treating infected women with antiretroviral medications can significantly reduce the risk of transmission. Women who are pregnant and infected with HIV should be treated during the 2nd and 3rd trimesters of pregnancy, during delivery, and during breastfeeding. Doing a cesarean delivery and treating the baby for several weeks after birth also reduce the risk. HIV is excreted in breast milk. Mothers infected with HIV should not breastfeed if they live in areas where formula feeding is safe and affordable. However, in areas where infectious diseases and undernutrition are common causes of infant death and where safe, affordable infant formula is not available, the World Health Organization recommends antiretroviral treatment combined with breastfeeding for at least 12 months. In such cases, the protection provided by breastfeeding from potentially fatal infections may counterbalance the risk of HIV transmission. Because many women with HIV infection and their infants are treated or take medications to prevent HIV infection, the number of Human Immunodeficiency Virus (HIV) Infection in Children and Adolescents is decreasing in many countries. Currently, HIV infection is rarely transmitted through blood transfusions or organ transplants. Since 1985 in most high-resource countries, all blood collected for transfusion is tested for HIV, and when possible, some blood products are treated with heat to eliminate the risk of HIV infection. The current risk of HIV infection from a single blood transfusion (which is carefully screened for HIV and other bloodborne viruses) is estimated to be less than 1 in about 2 million in the United States. However, in many low-resource countries, blood and blood products are not screened for HIV or are not screened as stringently. There, the risk remains substantial. HIV has been transmitted when organs (kidneys, livers, hearts, pancreases, bone, and skin) from infected donors were unknowingly used as transplants. HIV transmission is unlikely to occur when corneas or certain specially treated tissues (such as bone) are transplanted. HIV transmission is also possible when sperm from an infected donor is used to inseminate a woman. In the United States, measures have been taken to reduce this risk. Fresh semen samples are no longer used. Sperm from donors is frozen for 6 months or more. Then the donors are retested for HIV infection before the sperm is used. If a sperm donor is known to have HIV infection, washing sperm is an effective way to remove HIV from sperm. 