The New Age of Molecular Diagnostics for Microbial Agents

How, in this era of molecular diagnostic tests, can we best determine whether there is a causal relationship between the presence of a genetic signature of an infectious agent and disease? In recent years, molecular techniques have been applied successfully in the identification of infectious agents such as Borna virus, Kaposi's sarcoma–associated herpesvirus (human herpesvirus 8), West Nile virus, and the severe acute respiratory syndrome (SARS) coronavirus.1 Currently, the majority of surveillance and discovery efforts use methods based on sequences of known agents — namely, competitive polymerase chain reaction (PCR) and microarrays. Such efforts fail, however, when the agents in . . .