Modes of transmission and risk of spread

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HIV Transmission Rate

For the HIV virus pathogen to infect another person, it must meet both of the following conditions.

First, the amount of exposed virus must be sufficient to cause an infection.

The HIV virus is found in the blood, semen, vaginal secretions, and breast milk of infected patients, and exists in smaller amounts in pleural fluid and cerebrospinal fluid.

Second, the HIV virus must enter the bloodstream.

Infection occurs when the virus enters the body through the vaginal or rectal mucosa, directly into the bloodstream via a syringe needle, or when it penetrates the vascular system through broken skin such as wounds, eyes, nose, or the mucous membrane at the tip of the penis.

Routes of HIV Infection

  • The main routes of HIV infection are through sexual contact (unsafe sexual contact with an infected person), transfusion of infected blood (when receiving blood or blood products contaminated with HIV), sharing of contaminated syringes (when using a syringe used by an infected person), and mother-to-child transmission (during pregnancy, childbirth, or breastfeeding from an infected woman).
  • There is also a possibility of infection if exposure occurs during medical procedures performed by healthcare professionals. As of now, there have been no reported infections due to exposure among healthcare professionals in Korea.
HIV infection routes Content
Sexual contact Transmission route
HIV is transmitted when semen, vaginal fluids, or blood from an infected person enters the body of an uninfected person during sexual activity. HIV is found in semen and cervical/vaginal secretions, and it is more likely to be transmitted when there are signs of inflammation due to sexually transmitted infections, ulcers in the genital mucosa, or injuries to the genitals.
Infection probability
The probability of infection from a single sexual contact with an infected person is between 0.04% and 1.38%.

Exposure type (sexual contact) Risk per 10,000 exposures
Receptive Anal Intercourse 138
Insertive Anal Intercourse 11
Receptive Penile-Vaginal Intercourse 8
Insertive Penile-Vaginal Intercourse 4
Receptive Oral Intercourse Low
Insertive Oral Intercourse Low
※ Source: HIV Risk Behaviors, 2015 CDC)
Infection distribution
The most significant transmission route worldwide. In Korea, it has been found that over 99% of all HIV-infected individuals were infected through sexual contact, indicating that sexual contact plays a significant role in the spread of HIV.

Characteristics
Anal intercourse is the riskiest sexual behavior, and sexual contact without using condoms can lead to sexually transmitted infections such as chlamydia and gonorrhea. Even with condom use, some infections like syphilis and herpes can be transmitted through skin contact.
Transfusion of infected blood Transmission route
Infection occurs when a person receives a direct transfusion of blood infected with HIV or is administered serum produced from an infected person’s blood. The risk of HIV transmission is also high when transfusing blood products such as whole blood, concentrated red blood cells, platelets, white blood cells, and plasma.

Infection probability
The probability of infection from receiving a transfusion of infected blood is approximately 93%.

Exposure type Risk per 10,000 exposures
Blood Transfusion 9,250
※ Source: HIV Risk Behaviors, 2015 CDC
Infection distribution
Recently, thorough infection screening (including HIV screening tests and nucleic acid amplification tests) has been conducted on blood used for transfusions, and since 2006, there have been no reported cases of infection from blood transfusions.
Characteristics
Infection does not occur through gamma globulin, hepatitis B immunoglobulin, or plasma-derived hepatitis B vaccines.
Transmission route Transmission route
When a drug user abuses drugs through intravenous injection and shares their used syringe with others, HIV can be transmitted through the contaminated needle.

Infection probability
The probability of infection from shared use of a syringe needle is approximately 0.6%.

Exposure type Risk per 10,000 exposures
Needle-Sharing during Injection Drug Use 63
※ Source : HIV Risk Behaviors, 2015 CDC
Infection distribution
Five cases have been reported in Korea
Characteristics
In Korea, it is possible to purchase syringes without a doctor’s prescription, and the number of drug users who use syringes is low, resulting in significantly lower transmission rates due to shared syringe use compared to other countries.
Mother-to-child transmission Transmission route
Infection can occur through the placenta during pregnancy or during the childbirth process. Infection through breastfeeding is also possible.

Infection probability
The probability of mother-to-child transmission is approximately 23% (although individual differences exist, the average infection rate with preventive measures is 2-10%).

Exposure type Risk per 10,000 exposures
Mother-to-child transmission 2,260
※ Source : HIV Risk Behaviors, 2015 CDC
Infection distribution
In cases where infection is transmitted from an infected mother to the baby: Globally, 90% of HIV infections in newborns and children are mother-to-child transmissions.
Characteristics
Transmission is more likely from a mother with AIDS symptoms or a high viral load in the blood, and a mother infected with HIV during pregnancy has a relatively high amount of the virus in the early stages of infection, making fetal infection easier. However, if the currently implemented chemical prophylaxis is followed, a healthy baby can be born.

Statistics on HIV Transmission Routes in Korea

2023 Status of HIV/AIDS Reports in Korea: Epidemiological Survey on Routes of Transmission Statistics

Category Number of cases surveyed (individuals) %
Total sum 566 (100.0)
Sexual contact Between opposite genders
258		 (45.6)
Between same genders
306		 (54.1)
Mother-to-child transmission 0 (0.0)
Others 2 (0.4)

The investigation of transmission routes was conducted based on responses from the infected individuals during the epidemiological survey at health centers, excluding non-responses.
1) Shared use of syringes, etc. (Source: Korea Disease Control and Prevention Agency (2024). 2023 HIV/AIDS Notification Status Yearbook)

2010년부터 2023년까지 HIV/AIDS 전파 경로별 구성비 추이를 보여주는 누적 막대그래프

[Korean HIV/AIDS Cohort Study] Transmission Routes of Study Participants

Category Survey participants %
Total sum 1,509 100.0
Homosexual/Bisexual contact 953 63.2
Heterosexual contact 5431) 36.0
Mother-to-child transmission 0 0.0
Blood transfusion 4 0.4
Blood coagulation factor product 2 0.1
Shared use of drug syringes 1 0.1
Others2) 6 0.4
HIV/AIDS 신규 감염자의 전파 경로별 분포를 보여주는 막대그래프
The data is based on responses from participants in the “Korean HIV/AIDS Cohort Study” from 2006 to 2021, excluding non-responses.
  1. Includes one respondent who reported sexual contact.
  2. Infections due to acupuncture, tattoos, injection needles, etc.
Some statistical data may be changed according to the results of data refinement.
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