infectious diseases
Human Immunodeficiency Virus (HIV) Infection
Transmission of HIV Infection
Transmission of HIV requires contact with body fluids—specifically blood, semen, vaginal secretions, breast milk, or exudates from wounds or skin and mucosal lesions—that contain free HIV virions or infected cells. Transmission is more likely with the high levels of virions that are typical during primary infection, even when such infections are asymptomatic. Transmission by saliva or droplets produced by coughing or sneezing, although conceivable, is extremely unlikely. HIV is not transmitted by contact that does not involve exchange of body fluids. Transmission is usually Sexual: Direct transmission through sexual intercourse Needle- or instrument-related: Sharing of blood-contaminated needles or exposure to contaminated instruments Transfusion- or transplant-related Vertical: Transmission from an infected mother to child during pregnancy, childbirth, or through breast milk Sexual practices such as fellatio (oral sex done to a male) and cunnilingus (oral sex done to a female) appear to be relatively low risk but not absolutely safe (see table). Risk does not increase significantly if semen or vaginal secretions are swallowed. However, open sores in the mouth may increase risk. The sexual practices with the highest risks are those that cause mucosal trauma, typically intercourse. Anal-receptive intercourse poses the highest risk. Mucous membrane inflammation facilitates HIV transmission; sexually transmitted infections, such as Gonorrhea , Risk of transmission is increased in the early and advanced stages of HIV infection when HIV concentrations in plasma and genital fluids are higher. Evidence shows that people with HIV infection treated with antiretroviral therapy who have an undetectable viral load (virally suppressed) do not sexually transmit the virus to their partners ( Transmission references ). Circumcision seems to reduce the risk of males acquiring HIV infection by about 50%, by removing the penile mucosa (underside of foreskin), which is more susceptible to HIV infection than the keratinized, stratified squamous epithelium that covers the rest of the penis. Risk Risk Activity Activity None (unless sores are present) Dry kissing Body-to-body rubbing and massage Using unshared inserted sexual devices (eg, sex toys) Genital stimulation by a partner but no contact with semen or vaginal fluids Bathing or showering together Contact with feces or urine if skin is intact Theoretical (extremely low risk unless sores are present) Wet kissing Fellatio (oral sex done to a male) without ejaculation or if a condom is used Cunnilingus (oral sex done to a female) if a barrier is used Oral-anal contact Digital vaginal or anal penetration, with or without a glove Use of shared but disinfected inserted sexual devices Low Fellatio without a condom and with ejaculation Cunnilingus if no barrier is used Vaginal or anal intercourse if a condom is used correctly Use of shared but not disinfected inserted sexual devices High Vaginal or anal intercourse with or without ejaculation if a condom is not used or is not used correctly Risk of HIV transmission after skin penetration with a medical instrument contaminated with infected blood is on average about 1/300 without postexposure antiretroviral prophylaxis. Immediate prophylaxis probably reduces risk to < 1/1500. Risk appears to be higher if the wound is deep or if blood is inoculated (eg, with a contaminated hollow-bore needle). Risk is also increased with hollow-bore needles and with punctures of arteries or veins compared with solid needles or other penetrating objects coated with blood because larger volumes of blood may be transferred. Thus, sharing needles that have entered the veins of other people is a very high risk activity. Risk of transmission from infected health care practitioners who take appropriate precautions is unclear but appears minimal. In the 1980s, one dentist transmitted HIV to≥6 of his patients by unknown means. However, extensive investigations of patients cared for by other physicians infected with HIV, including surgeons, have uncovered few other cases. HIV can be transmitted from mother to offspring During pregnancy, transplacentally During childbirth Via breast milk The overall cumulative risk of vertical transmission without antiretroviral medications is 35 to 45% ( Transmission references ). Transmission rates can be reduced significantly by treating mothers with HIV infection with antiretroviral drugs while they are pregnant, in labor, and breastfeeding. Cesarean delivery and treatment of the infant for several weeks after birth also reduce the risk. HIV is excreted in breast milk. The overall risk of transmission through breastfeeding is approximately 14%, reflecting varying durations of breastfeeding and plasma viral RNA concentrations (eg, risk is high in women who become infected during pregnancy or during the period of breastfeeding) ( Transmission references ). In high-resource countries, women with HIV infection are advisednotto breastfeed (seeCenters for Disease Control and Prevention: Breastfeeding and Special Circumstances). However, in resource-limited settings, breastfeeding is associated with reduced infant morbidity and mortality due to malnutrition and infectious diseases. For women living with HIV in low-resource settings, the World Health Organization (WHO) recommends antiretroviral treatment and adherence support combined with breastfeeding for at least 12 months (seeWHO: Guidelines on HIV and Infant Feeding). Because many women with HIV infection and their infants are treated or take prophylactic antiretroviral medications during pregnancy, the incidence of AIDS in children is decreasing in many countries (see Human Immunodeficiency Virus (HIV) Infection in Infants and Children ). Screening of blood donors with tests for both antibody to HIV and HIV RNA has minimized risk of transmission via transfusion. Current risk of transmitting HIV via blood transfusion is estimated to be < 1/2,000,000 per unit transfused in the United States. However, in many high HIV burden countries, where blood and blood products are not screened for HIV, the risk of transfusion-transmitted HIV infection remains high. Rarely, HIV has been transmitted via transplantation of organs from HIV-seropositive donors. Infection has developed in recipients of kidney, liver, heart, pancreas, bone, and skin—all of which contain blood—but screening for HIV greatly reduces risk of transmission. HIV transmission is even more unlikely from transplantation of cornea,ethanol-treated and lyophilized bone, fresh-frozen bone without marrow, lyophilized tendon or fascia, or lyophilized and irradiated dura mater. HIV transmission is possible via artificial insemination using sperm from HIV-positive donors. Some cases of infection occurred in the early 1980s, before safeguards were introduced. In the United States, sperm washing is considered an effective method of reducing the risk of partner insemination from a known HIV-positive sperm donor. 1.Rodger AJ, Cambiano V, Bruun T, et al: Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study.Lancet393(10189):2428-2438, 2019. doi:10.1016/S0140-6736(19)30418-0 2.Rodger AJ, Cambiano V, Bruun T, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy [published correction appears inJAMA. 2016 Aug 9;316(6):667] [published correction appears inJAMA. 2016 Nov 15;316(19):2048].JAMA316(2):171-181, 2016. doi:10.1001/jama.2016.5148 3.Newell ML, Coovadia H, Cortina-Borja M, et al: Mortality of infected and uninfected infants born to HIV-infected mothers in Africa: a pooled analysis.Lancet364(9441):1236-1243, 2004. doi:10.1016/S0140-6736(04)17140-7 4.Dunn DT, Newell ML, Ades AE, Peckham CS: Risk of human immunodeficiency virus type 1 transmission through breastfeeding.Lancet340(8819):585-588, 1992. doi:10.1016/0140-6736(92)92115-v 