From Evidence to Exposure: Biological and Infectious Hazards in Forensic DNA Practice from Crime Scene to Laboratory

Forensic biological evidence has a dual identity: it is an evidential substrate that must be protected from contamination and, in some circumstances, a potential source of occupational biological exposure. This focused narrative review maps that second problem across the forensic DNA pathway, from scene collection and packaging through evidence receiving, examination, biological screening, DNA pre-processing, storage, and disposal. Three distinctions anchor the synthesis: DNA relevance is not the same as infectious-risk relevance; pathogen detection is not equivalent to viable infectivity; and the presence of a biological hazard is not the same as an effective occupational exposure or transmission event. The review prioritises hepatitis B virus, hepatitis C virus, human immunodeficiency virus, tuberculosis, respiratory pathogens, sharps injuries, and context-dependent hazards, while examining how evidence state, handling task, exposure route, and control effectiveness interact. Experimental and postmortem studies show that drying, decomposition, refrigeration, or elapsed time cannot serve as universal indicators of biological safety, although persistence data should not be translated directly into casework transmission probabilities. A pathway-based control model is developed in which engineering and work-practice controls, personal protective equipment, vaccination, training, incident reporting, and post-exposure pathways are integrated with evidence-preservation requirements. The major unresolved problems are forensic-specific: denominator-based exposure data are scarce, leaking packages and concealed sharps are poorly quantified, aerosol-generating DNA preparation has received little direct study, and engineering-control evaluations remain uncommon. Treating biosafety as part of evidence management provides a practical route to strengthen worker protection without separating occupational safety from the quality systems that protect forensic DNA evidence.