What is the risk of HIV transmission from dried blood on a surface that is several years old?

Risk of HIV Transmission from Years-Old Dried Blood

There is essentially zero risk of HIV transmission from dried blood that is several years old on a knife surface. HIV does not survive drying and environmental exposure for extended periods, making transmission from years-old dried blood impossible in practical terms.

HIV Viability in Dried Blood

• HIV loses viability rapidly once blood dries and is exposed to environmental conditions. 1
• Less than 1% of HIV viruses remain viable after one week of storage at elevated room temperature. 1
• Viable HIV is recovered from only 8% of needles after 21 days at room temperature, and this represents fresh needlestick scenarios with hollow-bore needles—not dried surface blood. 1
• After years of environmental exposure, no viable HIV would remain on a dried surface like a knife. 1

Context: Actual HIV Transmission Risks

To understand why years-old dried blood poses no risk, consider the documented transmission risks from fresh exposures:

• Percutaneous injury (needlestick) with fresh HIV-infected blood: 0.3% risk (95% CI = 0.2%-0.5%). 2
• Mucous membrane exposure to fresh HIV-infected blood: 0.09% risk (95% CI = 0.006%-0.5%). 2
• Nonintact skin exposure to fresh HIV-infected blood: Less than 0.09% risk, though not precisely quantified. 2

These already-low risks apply only to fresh, wet blood from a known HIV-positive source with active viremia. 2

Why Dried Blood Eliminates Risk

• HIV requires specific conditions to remain infectious, including moisture and protection from environmental degradation. 1
• The drying process itself rapidly inactivates HIV particles. 1
• Even in research settings with optimal conditions, HIV viability drops precipitously within days. 1
• No documented cases of HIV transmission from dried blood on environmental surfaces exist in medical literature, despite decades of surveillance. 1

Risk Factors That Increase Transmission (None Apply Here)

For context, documented HIV transmission requires:

• Large quantity of fresh blood from a source with high viral load. 2
• Deep percutaneous injury with a hollow-bore needle visibly contaminated with blood. 2
• Direct placement of the device in a vein or artery of the HIV-positive source. 2
• Terminal illness in the source patient, reflecting higher viral titers. 2

None of these factors are present with years-old dried blood on a surface. 1

Clinical Reassurance

• The patient's concern about years-old dried blood represents no meaningful HIV exposure risk. 1
• No post-exposure prophylaxis, testing, or follow-up is indicated for contact with years-old dried blood. 2, 1
• This scenario does not meet the CDC definition of an HIV exposure requiring clinical evaluation. 2

Common Pitfall to Avoid

• Do not conflate theoretical concerns with actual transmission risk. While HIV can be detected by sensitive laboratory techniques in dried blood for research purposes, detection does not equal infectivity or transmission capability. 1
• The distinction between "detectable" and "viable/infectious" virus is critical—after years of environmental exposure, no infectious virus remains. 1