Superposed images of herpes-infected squamous cells (image by Edward O. Uthman, Brown & Associates Medical Laboratories, LLP, USA and obtained via Flickr) and the schematic drawing of urethral exudate containing Neisseria gonorrhoeae (image by Dr. Norman Jacobs, Center for Disease Control and Prevention, USA and obtained via the CDC Public Health Image Library , ID#3693); images modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.