Bloodborne pathogens (BBPs) are microorganisms found in human blood that can cause disease. These infectious agents are transmitted when infected blood or specific body fluids enter another person’s bloodstream. Understanding the routes of transmission is important for preventing infection, especially for those in healthcare or other high-risk environments. The three bloodborne pathogens of most concern are the Human Immunodeficiency Virus (HIV), the Hepatitis B Virus (HBV), and the Hepatitis C Virus (HCV). Although these three viruses share certain modes of transmission, their specific infectivity and survival rates outside the body can differ significantly.
Direct Entry Through Skin and Mucous Membranes
Transmission often occurs through a breach in the body’s natural defenses, such as a cut or puncture wound that allows infected fluid to enter the bloodstream directly. Needlestick injuries, cuts from broken glass, or contact with any contaminated instrument that pierces the skin can inoculate a person with the pathogen. This represents a primary route for occupational exposure to BBPs, particularly for healthcare workers.
The risk of becoming infected with HBV after a single needlestick exposure is estimated to be up to 30%, which is significantly higher than the approximate 0.3% risk for HIV. This difference is partly due to HBV’s high concentration in the blood and its ability to survive longer on environmental surfaces. Beyond needlesticks, the sharing of contaminated injection equipment, such as needles and syringes, is a major non-occupational route of transmission for HIV, HBV, and HCV.
Contact between infected fluids and non-intact skin also poses a risk, which includes areas with cuts, abrasions, dermatitis, or even severe acne. Mucous membranes are another entryway for pathogens when exposed to splashes or sprays of infected blood or body fluids. The rate of HIV transmission from a mucous membrane exposure is estimated to be about 0.1%, which is lower than a percutaneous injury.
The sharing of personal items that can draw blood, such as toothbrushes or razors, is a potential route of transmission. Historically, receiving contaminated blood transfusions or blood products was a major route of BBP transmission, but modern, rigorous screening and testing of all donated blood has made this mode extremely rare in developed nations.
Sexual Contact and Fluid Exchange
Sexual contact is a primary mode of transmission for several BBPs, especially HIV and HBV. The pathogens are carried in fluids like semen, pre-ejaculatory fluid, rectal fluids, and vaginal fluids, and can enter the body through mucous membranes lining the rectum, vagina, penis, or mouth. The presence of micro-tears or abrasions in these tissues, which can occur during unprotected intercourse, facilitates the entry of the virus into the bloodstream.
Unprotected penetrative sexual activity carries a risk because it can cause microscopic trauma to the tissues, increasing the likelihood of fluid-to-fluid or blood-to-fluid contact. While both HBV and HIV are efficiently transmitted this way, HCV is less likely to be sexually transmitted, though the risk increases with high-risk practices or the presence of other sexually transmitted infections. The risk of transmission can be elevated during menstruation, as the presence of blood can increase the viral load exchanged.
Vertical Transmission (Mother to Child)
Vertical transmission occurs when a pathogen is passed from an infected parent to their offspring. This transmission can occur at three different time points: during pregnancy, during labor and delivery, or post-birth. The highest risk for mother-to-child transmission (MTCT) of bloodborne viruses typically occurs during the peripartum phase, or the process of childbirth.
During labor and delivery, the infant may be exposed to the mother’s blood and vaginal fluids, potentially leading to infection through ingestion or contact with the newborn’s mucous membranes. Transmission can also occur in utero, when the pathogen crosses the placental barrier to infect the fetus directly. The risk of this transplacental infection is highly dependent on the mother’s viral load and the specific pathogen involved.
Postpartum transmission primarily happens through breastfeeding, as certain pathogens like HIV can be present in breast milk. For known carriers of BBPs, medical interventions are available to mitigate the risk of MTCT. These interventions often involve antiviral therapy for the mother during pregnancy, specific medication given to the baby after birth, and sometimes a planned cesarean delivery or avoidance of breastfeeding to prevent exposure.