Dried blood refers to blood that has undergone a drying process, often observed as a reddish-brown residue on surfaces. It can form when fresh blood is blotted onto absorbent materials or simply dries in the air. A common application for dried blood is in dried blood spot (DBS) testing, where small blood samples are collected on filter paper for laboratory analysis. The question of whether dried blood can transmit disease is complex, as the risk is not a simple yes or no, but rather depends on various contributing factors.
Factors Influencing Pathogen Survival
The ability of a pathogen to survive in dried blood outside the body is influenced by several environmental and biological factors. Temperature and humidity play a significant role, as extreme temperatures and very low humidity can degrade pathogens more quickly. Viruses often lose viability faster in higher temperatures and higher relative humidity, while some bacteria might persist longer in cooler, more humid environments. Some pathogens are inherently hardier than others, allowing them to withstand harsh conditions for longer periods.
The initial concentration of the pathogen, known as the viral or bacterial load, also impacts survival; a higher load can increase the chance of pathogens remaining viable outside a host. The type of surface material where the blood dries can affect pathogen longevity. For example, some bacteria can survive for months on dry surfaces like stainless steel, while others may persist for only days. Porous surfaces can sometimes offer protection to pathogens, extending their survival compared to non-porous surfaces. Additionally, the presence of organic material within the blood itself can provide a protective buffer for pathogens, shielding them from immediate degradation and potentially prolonging their survival.
Bloodborne Pathogens and Transmission Risk
The risk of disease transmission from dried blood varies significantly depending on the specific bloodborne pathogen involved. Human Immunodeficiency Virus (HIV) is particularly fragile outside the body. The virus quickly becomes inactive when exposed to air, meaning the risk of HIV transmission from dried blood is extremely low, or virtually zero. While some studies suggest HIV can survive in dried blood at room temperature for several days, the concentration of viable virus is typically very low, and it becomes nonviable for infection.
In contrast, Hepatitis B Virus (HBV) is considerably more resilient and can survive in dried blood for at least seven days, and potentially longer, at room temperature. This extended viability means there is a moderate risk of HBV transmission from dried blood, especially if contact occurs with broken skin or mucous membranes like the eyes, nose, or mouth. Hepatitis C Virus (HCV) also demonstrates some environmental stability, with studies indicating it can remain infectious on surfaces for up to six weeks at various temperatures. However, the risk of transmission from dried blood for HCV is generally considered low to very low. Overall, bloodborne pathogens typically transmit through direct contact with infected blood entering the bloodstream, such as via needlestick injuries, or through contact with open wounds or mucous membranes.
Safe Handling and Prevention
Taking appropriate precautions when encountering dried blood is important to minimize any potential risk of pathogen transmission. Wearing personal protective equipment (PPE), such as disposable gloves, is recommended before handling or cleaning up blood spills. After donning gloves, the area should be cleaned using an EPA-approved disinfectant, such as a solution of household bleach (one part bleach to ten parts water), which is effective against many bloodborne pathogens.
Contaminated cleaning materials, including gloves and wipes, should be carefully disposed of in a sealed plastic bag. Thorough hand hygiene, including washing hands with soap and water immediately after cleanup, is an important final step to remove any potential residues. If significant exposure occurs, such as a needlestick injury or direct contact with an open wound, or if there is uncertainty about the risk, seeking medical advice promptly is advisable.