Cocaine surface contamination and the medico-legal implications of its transfer

The question posed by this research involves how frequently one can expect to contact cocaine in day-to-day living experiences where drug use may not normally be suspected. Issues concerning contamination are germane to medico-legal investigators who evaluate the significance of drug test results in (1) questioned deaths, (2) public health concerns, (3) drugs crimes, and (4) drug use toxicological tests potentially caused by external contamination, such as hair, sweat, and skin swabs. Previous surface studies focus mainly on currency drug contamination; few have addressed other common surfaces. Public surfaces handled by a large number of people, such as building entrance door handles, bank currency dispensing machines, food store shopping carts, and service station fuel pumps within the New Haven, Connecticut metropolitan area were tested. Socio-economically, the distribution of items tested ranged from working-class to upper-middle class areas. Results were obtained using the Securetec Drugwipe II® which is an immunological, on-site test device. Precautions were taken to avoid carry-over and other potential contamination from handling including single-use latex gloves which were pre-tested as a negative control immediately before swabbing. Analysis was performed according to the manufacturer’s instructions and in the laboratory to standardize conditions. Drugwipe II® limit of detection (LOD) is ∼50 ng. Test results revealed 78% positive for cocaine substances as follows: fuel pump buttons for credit card authorization, 100% positive (n = 10 individual locations); ATM machines for currency withdrawal, 100% positive (n = 10 individual locations); grocery store shopping carts, 70% positive; academic building entrance doors, 30% positive (n = 10); and shopping mall entrance/exit doors, 100% positive (n = 5). Forensic scientists and medico-legal investigators responsible for interpreting surface test results are cautioned to consider contamination before ascribing drug activity to a specific individual. For legal proceedings these results are indicative but not conclusive because immunological tests are considered presumptive and may react with the parent substance (cocaine), related compounds (benzoylecgonine, ecgonine methyl ester, ecgonine, nor-ecgonine, and cocaethylene) and immunologically similar materials.