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Transmission

October 2008

HIV is spread most often through unprotected sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex.


Risky Behavior

HIV can infect anyone who practices risky behaviors such as

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  • Sharing drug needles or syringes
  • Having sexual contact, including oral sexual contact, with an infected person without using a condom
  • Having sexual contact with someone whose HIV status is unknown


Infected Blood

HIV also is spread through contact with infected blood. Before donated blood was screened for evidence of HIV infection and before heat-treating techniques to destroy HIV in blood products were introduced, HIV was transmitted through transfusions of contaminated blood or blood components. Today, because of blood screening and heat treatment, the risk of getting HIV from blood transfusions is extremely small.


Contaminated Needles

HIV is often spread among injection drug users when they share needles or syringes contaminated with very small quantities of blood from someone infected with the virus.

It is rare for a patient to be the source of HIV transmitted to a healthcare provider or vice versa by accidental sticks with contaminated needles or other medical instruments.


Mother to Child

Women can transmit HIV to their babies during pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus.

  • If the mother takes certain drugs during pregnancy, she can significantly reduce the chances that her baby will get infected with HIV.
  • If healthcare providers treat HIV-infected pregnant women and deliver their babies by cesarean section, the chances of the baby being infected can be reduced to a rate of 1 percent.

HIV infection of newborns has been almost eradicated in the United States because of appropriate treatment.

A study sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) in Uganda found a highly effective and safe drug for preventing transmission of HIV from an infected mother to her newborn. Independent studies have also confirmed this finding. This regimen is more affordable and practical than any other examined to date. Results from the study show that a single oral dose of the antiretroviral drug nevirapine (NVP) given to an HIV-infected woman in labor and another to her baby within 3 days of birth reduces the transmission rate of HIV by half compared with a similar short course of AZT (azidothymidine).


Saliva

Although researchers have found HIV in the saliva of infected people, there is no evidence that the virus is spread by contact with saliva. Laboratory studies reveal that saliva has natural properties that limit the power of HIV to infect, and the amount of virus in saliva appears to be very low. Research studies of people infected with HIV have found no evidence that the virus is spread to others through saliva by kissing.

The lining of the mouth, however, can be infected by HIV, and instances of HIV transmission through oral intercourse have been reported.

Scientists have found no evidence that HIV is spread through sweat, tears, urine, or feces.


Casual Contact

Studies of families of HIV-infected people have shown clearly that HIV is not spread through casual contact such as the sharing of food utensils, towels and bedding, swimming pools, telephones, or toilet seats.

HIV is not spread by biting insects such as mosquitoes or bedbugs.


Sexually Transmitted Infections

People with a sexually transmitted infection, such as syphilis, genital herpes, chlamydia, gonorrhea, or bacterial vaginosis, may be more susceptible to getting HIV infection during sex with infected partners.





  
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This article was provided by U.S. National Institute of Allergy and Infectious Diseases. It is a part of the publication Understanding HIV/AIDS.
 

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