A blood-borne infection (BBI) is a disease-causing pathogen transmitted through contact with infected human blood. These infectious agents, which include viruses, bacteria, and parasites, can enter the bloodstream through various means. Identifying the most prevalent infection is key to understanding the burden of BBIs in the United States.
The Most Prevalent Blood-Borne Infection in the US
The most common blood-borne infection in the United States is the Hepatitis C Virus (HCV). HCV is an RNA virus that primarily targets the liver, causing inflammation and damage. Approximately 2.2 to 4.0 million people in the U.S. are currently living with HCV, a prevalence rate higher than that of HIV and Hepatitis B Virus (HBV).
The Centers for Disease Control and Prevention (CDC) estimated about 69,800 new acute HCV infections in 2021. This increase is largely attributed to the opioid epidemic and associated injection drug use. Many individuals with chronic HCV are unaware of their status; estimates suggest only about 56% of infected persons have been diagnosed. This lack of awareness contributes to continued transmission and progression to advanced liver disease.
Understanding Transmission Routes and Risk Factors
HCV spreads primarily through direct blood-to-blood contact. The most significant transmission route in the U.S. is the sharing of needles, syringes, or other equipment used for injecting drugs. Trace amounts of blood, even if unseen, can harbor the virus and cause infection.
Percutaneous exposures also carry risk, including accidental needlestick injuries in healthcare settings. Receiving tattoos or body piercings with improperly sterilized equipment is another documented route. Historically, blood transfusions and organ transplants received before 1992 were major sources of transmission, prior to widespread screening of the blood supply.
Transmission from an infected mother to her child during birth occurs in approximately 6% of cases. Sexual transmission is less efficient than percutaneous exposure, but the risk increases with multiple partners or high-risk sexual practices. Sharing personal items like razors or toothbrushes contaminated with blood is a rare means of spread.
Recognising the Stages of Infection and Diagnosis
Every HCV infection begins as an acute phase, lasting the first six months after exposure. This stage is often asymptomatic, presenting with only mild, non-specific complaints like fatigue. While the immune system spontaneously clears the virus in a minority of cases, the infection persists for most people.
If the virus remains for longer than six months, the infection becomes chronic, potentially lasting a lifetime. Chronic HCV slowly causes inflammation and scarring in the liver, which can lead to cirrhosis, liver failure, or liver cancer over many years. Since the chronic phase can remain silent for decades, many people are unaware they are infected until advanced liver damage occurs.
Diagnosis typically begins with a blood test screening for HCV antibodies, indicating exposure. If the antibody test is positive, a second test detects the viral genetic material (RNA), confirming a current, active infection. Universal screening is now recommended for all adults aged 18 and older, in addition to risk-based testing. Early diagnosis allows for treatment before severe liver damage develops.
Current Treatment Protocols and Prevention
The treatment landscape for Hepatitis C has been revolutionized by Direct-Acting Antivirals (DAAs). These medications are highly effective, well-tolerated, and have cure rates exceeding 95%. Treatment involves taking oral medications for a short duration, typically 8 to 12 weeks. Achieving a Sustained Virologic Response (SVR)—undetectable HCV RNA 12 weeks after treatment—is considered a cure.
A cured patient is no longer at risk of developing HCV-related liver cancer or cirrhosis and cannot transmit the virus. Prevention efforts focus on harm reduction strategies to limit blood-to-blood contact, especially among people who inject drugs. Needle exchange programs provide sterile equipment and are a key public health measure.
Healthcare facilities must adhere to universal precautions and safe injection practices to protect workers and patients from occupational exposure. Unlike Hepatitis B, no vaccine is currently available to prevent HCV infection. Therefore, screening, early diagnosis, and access to curative DAA treatment remain the primary strategies for controlling the virus.