Obtaining rapid and reliable diagnosis of infectious diseases is usually limited by the sensitivity of the detection technology. Even in severe sepsis, accompanied by organ failure and admission to an intensive care unit, the causative organism is often present at a level of less than one bacterium per milliliter of blood. Similarly, in candidiasis the yeast cells are present at vanishingly low levels in body fluids, while in chlamydia infections the pathogen is located intracellularly as is entirely absent from