XCULP: The Great Reduction and Procreation    by Ken Tennen
Price: $19.99 USD. 104030 words. Published on July 12, 2011. .
An asteroid named "XCULP" contained a virus that caused earth's human population to drop from seven billion to seven million. This double-volume book chronicles the survivors' struggle to maintain civilization and to populate as fast as possible. Some strong language and some descriptions of sex.