Helpful resources:
www.cdc.gov/hiv/bscience.htm
www.cdc.gov/mmwr/preview/mmwrhtml/00018871.htm
www.cdc.gov/hiv/pubs/faq/faq8.htm
www.cdc.gov/hiv/pubs/faq/faq26.htm
www.cdc.gov/mmwr/PDF/rr/rr5011.pdf