Glynn, S., Busch, M., Schreiber, G., et al. (2003). Effect of a National Disaster on Blood Supply and Safety: The September 11 Experience. Journal of the American Medical Association. 289(17): 2246-2253.
The authors examine data gathered four weeks before and after 9/11/2001 and compared it to the same period in 2000. They found an increase in donations and a three-fold increase in donations confirmed positive for certain viruses (e.g., HIV and hepatitis B and C) one week before September 11 (0.1%) and one week after the attacks (0.3%). This was explained by the increase in first-time and lapsed repeat donors. The authors emphasize the need for better education that could encourage repeat donations.