Researchers are conducting studies to investigate whether a daily pill or combination of drugs can prevent HIV infection in humans. The New York Times reports that the test of preventative treatment against HIV using antiretroviral drugs--called PrEP for pre-exposure prophylaxis--are expected to have more participants in the next year than studies of vaccines and microbicides to cure infection. PrEPs are already being used successfully to cut down the rate of HIV transmission between HIV-infected pregnant women and their unborn children. Scientists in Peru and Ecuador are already conducting studies of PrEP to combat the disease. The National Institute of Health, the Centers for Disease Control, and the Bill and Melinda Gates Foundation are providing funding for the studies. Saturday the Centers for Disease Control announced that reports of HIV infection have previously undercounted the number of people who are HIV positive and that the actual population in the U.S. may be 40% larger than thought.