When Clostridium difficile was first identified in 1935, in the stools of healthy neonates, it was named Bacillus difficilis by its discoverers. They chose the specific name difficilis to reflect the difficulty they had had in isolating and culturing the organism. It’s ironic that the label is still appropriate, now that controlling the growth and spread of this bacterium is the problem (NEJM 2008; 359:1932-40, doi:10.1056/NEJMra0707500).

In the 1980s, the genital variant of herpes simplex virus was seen as a new and threatening sexually transmitted disease. As an editorial in Sexually Transmitted Infections (2008;84:330-1, doi:10.1136/sti.2008.032003) remarks, it even made the cover of Time magazine. This threat was rapidly eclipsed by that of HIV, and the focus of research changed. Even now, evidence about risks and harms of screening for genital herpes infection is inadequate to formulate a rational public health policy.

Everyone agrees that new …