Courtesy of Health.com (Courtesy of Health.com)

On Saturday, December 1, people around the globe who come together to recognize the 25th World AIDS Day will have much to mourn and also much to celebrate. Over the past quarter-century, 25 million lives have been lost to HIV/AIDS, but remarkable strides have also been made in halting the disease's progression.

World AIDS Day, which was conceived by the World Health Organization to raise awareness and support, is an opportunity to take stock of the epidemic's scope and the everyday impact of the virus. What better way to do this than by reminding ourselves of the often alarming numbers involved?

The stories of individuals who have lived with HIV/AIDS, or who have who suffered a loss at its hands, will always have a unique power. But the following statistics, gathered from government data and scientific research, provide a bird's-eye view that brings home the vastness and complexity of the epidemic.

1.15 million

Estimated number of HIV-positive people in the United States

This figure works out to about 1 in every 200 people over the age of 13. What's more, nearly 20% of these people don't know they're infected because they haven't been tested for the virus.

Worldwide, an estimated 34.2 million people are living with HIV/AIDS—two-thirds of them in sub-Saharan Africa. While the rate in the United States may seem low by comparison, it still is one of the highest in the developed world, says Michael Horberg, MD, director of HIV/AIDS at Kaiser Permanente, the nation's largest nonprofit health plan. (In the U.K., for instance, roughly 1 in 650 people are estimated to be HIV-positive.)

21,601

Estimated annual U.S. deaths from HIV/AIDS

This statistic, from 2009 (the most recent year for which solid data is available), is heartbreaking yet also encouraging: It's less than half the number of people who died of HIV/AIDS in 1995, when mortality reached an all-time high.

The sharp decrease is a testament to improved testing, diagnosis, and treatment. "This number, while still too high, shows that quality HIV care, and the potent medications we now have, [have] dramatically improved the lives of HIV-positive Americans and people worldwide," Horberg says.

1,000

People ages 13 to 24 newly infected with HIV in the United States each month

Young people now account for 1 in every 4 new infections in the United States, according to a report released this week by the Centers for Disease Control and Prevention (CDC).

Even more troubling, 60% of these individuals don't know their status, making transmission easier and treatment harder. Only 35% of 18- to 24-year-olds and just 22% of sexually active high-school students have been tested, according to the report.