Addiction and Infectious Disease: HIV, Hepatitis C, and Prevention

Introduction

Substance use disorders are major drivers of infectious disease transmission — particularly HIV and hepatitis C virus (HCV). Injection drug use is responsible for approximately 10% of new HIV infections and 30% of new HCV infections in the United States. Beyond injection drug use, substance use impairs judgment and increases sexual risk-taking, contributing to sexually transmitted infections including HIV. Understanding the relationship between addiction and infectious disease — and the evidence-based strategies for prevention and treatment — is essential for comprehensive addiction care.

Key Definitions

Injection drug use (IDU): The intravenous, intramuscular, or subcutaneous injection of drugs. The primary route of HIV and HCV transmission associated with drug use.

Hepatitis C virus (HCV): A bloodborne virus that causes liver inflammation and, with chronic infection, cirrhosis and liver cancer. Highly prevalent among people who inject drugs.

Pre-exposure prophylaxis (PrEP): A medication regimen (tenofovir/emtricitabine) that dramatically reduces HIV transmission risk when taken consistently.

Direct-acting antivirals (DAAs): Highly effective medications for HCV that cure infection in over 95% of cases with 8-12 weeks of treatment.

Harm reduction: Strategies that reduce the risk of infectious disease transmission without requiring abstinence from drug use.

HIV and Injection Drug Use

Injection drug use is a major driver of HIV transmission through the sharing of contaminated needles and syringes. Key facts:

Approximately 10% of new HIV diagnoses in the United States are attributed to injection drug use.
People who inject drugs are 22 times more likely to acquire HIV than the general population.
HIV transmission through injection drug use disproportionately affects Black and Hispanic communities and rural populations.
Substance use — including non-injection use — also increases HIV risk through impaired judgment and increased sexual risk-taking.

Prevention strategies:

Syringe service programs (SSPs): Providing sterile syringes reduces HIV transmission by 50% among people who inject drugs. SSPs are one of the most evidence-based HIV prevention interventions.
Medication-assisted treatment: MAT — particularly methadone and buprenorphine — reduces injection drug use and associated HIV risk. People on MAT are significantly less likely to share needles.
Pre-exposure prophylaxis (PrEP): PrEP reduces HIV transmission risk by over 99% when taken consistently. It should be offered to people who inject drugs and are at risk of HIV.
HIV testing: Regular HIV testing allows early diagnosis and treatment, which reduces transmission (undetectable = untransmittable).

Hepatitis C and Injection Drug Use

HCV is even more prevalent than HIV among people who inject drugs, due to its higher transmissibility through blood contact:

Approximately 50-80% of people who inject drugs are infected with HCV.
HCV is 10 times more transmissible than HIV through needle sharing.
Injection drug use accounts for approximately 30% of new HCV infections in the United States.
Untreated chronic HCV causes cirrhosis in 15-30% of infected people and is a leading cause of liver transplantation.

Treatment revolution: The development of direct-acting antivirals (DAAs) has transformed HCV treatment. DAAs cure HCV in over 95% of cases with 8-12 weeks of oral treatment, with minimal side effects. This represents a dramatic improvement over older interferon-based treatments, which had cure rates of 40-50% and significant side effects.

People who inject drugs can and should be treated for HCV — research has shown that treatment outcomes are comparable to those in non-drug-using populations, and that treatment does not require abstinence from drug use. Treating HCV in people who inject drugs also reduces transmission to others.

Prevention: SSPs reduce HCV transmission by 50-80% among people who inject drugs. MAT also reduces HCV risk by reducing injection drug use.

Other Infectious Diseases

Bacterial infections: Injection drug use is associated with a range of bacterial infections, including skin and soft tissue infections (abscesses, cellulitis), endocarditis (infection of the heart valves), and sepsis. These infections are increasingly caused by methicillin-resistant Staphylococcus aureus (MRSA) and are a major cause of hospitalization and death among people who inject drugs.

Sexually transmitted infections: Substance use — particularly stimulant use — is associated with increased sexual risk-taking and elevated rates of sexually transmitted infections including HIV, syphilis, gonorrhea, and chlamydia.

COVID-19: People with substance use disorders have elevated rates of COVID-19 infection and worse outcomes, reflecting both behavioral risk factors and the health consequences of addiction.

Integrated Treatment

Integrating infectious disease prevention and treatment with addiction treatment produces better outcomes than treating these conditions separately:

Co-located services: Providing HIV and HCV testing, prevention, and treatment in addiction treatment settings increases access and reduces barriers.

Linkage to care: People who are diagnosed with HIV or HCV in addiction treatment settings should be linked to infectious disease care. Warm handoffs — direct referrals with follow-up — are more effective than simple referrals.

MAT as HIV/HCV prevention: MAT reduces injection drug use and associated infectious disease risk. Expanding access to MAT is an important HIV and HCV prevention strategy.

Frequently Asked Questions

Can I be treated for HCV if I still use drugs?
Yes. Current guidelines recommend treating HCV in people who use drugs, without requiring abstinence. Treatment outcomes are comparable to those in non-drug-using populations. Treating HCV in people who use drugs also reduces transmission to others.

Does MAT reduce HIV and HCV risk?
Yes. MAT — particularly methadone and buprenorphine — significantly reduces injection drug use and associated HIV and HCV risk. People on MAT are significantly less likely to share needles and are more likely to engage in HIV and HCV prevention and treatment.

What is PrEP and should I take it?
PrEP (pre-exposure prophylaxis) is a medication regimen that reduces HIV transmission risk by over 99% when taken consistently. It should be considered by anyone at risk of HIV, including people who inject drugs. Talk to your healthcare provider about whether PrEP is appropriate for you.

Key Takeaways

Injection drug use is a major driver of HIV and HCV transmission — approximately 10% of new HIV infections and 30% of new HCV infections are attributed to injection drug use.
SSPs, MAT, and PrEP are evidence-based strategies for reducing HIV and HCV transmission among people who inject drugs.
Direct-acting antivirals cure HCV in over 95% of cases and should be offered to people who use drugs without requiring abstinence.
Integrating infectious disease prevention and treatment with addiction treatment produces better outcomes than treating these conditions separately.
Treating infectious diseases in people with addiction is both clinically important and a public health priority.

Additional Resources

Related articles on Sobriety Navigator: Opioid Use Disorder, Harm Reduction Approaches, Medication-Assisted Treatment, Polysubstance Use.