Counting Beans

A Look at Epidemiology

September/October 2007

Nothing could be more boring than statistics and numbers. But no matter if you're reading or hearing them, there is no best way to best understand the scope of an epidemic. It's important to get a grasp of the numbers of people with HIV so that we can inform policy, economic and political decisions that can eventually change the scope of an epidemic.

Epidemiology is the study of disease in human populations. We think of it as numbers and statistics that can tell us where and when people are impacted or infected and basically anything you might want to know about a disease or disease characteristic.

The U.S. Centers for Disease Control and Prevention (CDC) is the federal agency that collects statistics on all diseases in the United States, and publishes the data in order to inform policy and health care decisions. Check out the CDC website at Unfortunately, the data is not necessarily timely. HIV/AIDS information is not released every year by the CDC, so other sources may be useful, such as local health departments or other smaller analyses being performed by different localities or universities.

Based on estimates, at the end of 2003 there were 1,039,000 to 1,185,000 persons in the United States living with HIV/AIDS. In 2005, 37,331 cases of HIV/AIDS in adults, adolescents, and children were diagnosed in the 33 states that are reporting confidential name-based HIV reporting. The CDC has estimated that approximately 40,000 persons in the United States become infected with HIV each year.

In 2005, the most current CDC analysis, almost three quarters of HIV cases were in men, the rest in women (no counting of transgender people), and 67% of those men are men who have sex with men (MSM). Blacks account for almost half of infections in 2005 yet are only 13% of the U.S. population. Whites account for 31%; Hispanics are 18%. Asian/Pacific Islander and American Indian/Alaskan Native account for 1% each.

According to HIV/AIDS surveillance (a close watch, examination, or inspection) data, AIDS cases have remained stable for the past 10 years in the U.S., the most being seen in urban areas. (CDC defines urban as greater than 500,000 population.) The South is seeing the highest numbers of newly reported AIDS cases, as we have been hearing. Blacks are the highest proportion of AIDS cases in urban areas but not in the rest of the country, where the cases are about the same in white and black. More than half of cumulative AIDS cases have been in males who have had male-to-male sexual contact. Of great concern is that women are almost twice as likely to have been infected by high-risk males and not through injection drug use.

40% of the AIDS cases reported in 2005 were among adults age 35 to 44 years at their time of diagnosis. Nearly 23% were among adults age 25 to 34 years, and an additional 24% were among adults age 45 to 54 years. Eight percent of cases in each category were among adults age 55 years and older at diagnosis, and 5% in persons younger than 25.

The good news is what you'd expect to see in an epidemic where effective treatments became available, yet prevention efforts need to be strengthened. The numbers of HIV/AIDS cases is increasing as people are living longer while AIDS mortality (death) has decreased. More people are getting tested, which also may explain the rising numbers of cases.

But what about the rest of the world where 90% of all HIV/AIDS exists? The World Health Organization (WHO) estimates 39.5 million people living with HIV. 65% of new cases are occurring in sub-Saharan Africa while in Eastern Europe and Central Asia cases have risen by 50% since 2004. These estimates might not include people who may be more difficult to be identified due to stigma and denial. In 2006, 2.9 million people died of AIDS-related illnesses.

The global pandemic (widespread epidemic affecting many countries) continues to grow and some countries that had stabilized or saw declining rates may now be seeing a resurgence. However, there are declines in other countries and now treatment is scaling up in places where the epidemic was raging unabated. (Check out the WHO website for country by country statistics,

There are many other websites with epidemiological information. The Henry J. Kaiser Family Foundation website is another great place to retrieve and decipher epidemiological information, Universities such as Johns Hopkins ( and the University of California at San Francisco ( have great informational HIV/AIDS websites, including the statistics. Don't forget, the Internet search engine Google is an extensive -- though somewhat overwhelming -- place to look for further information. A basic rule of thumb, however, is that the CDC and WHO have the most credible stats, and most other organizations and agencies use their numbers to report to their clients and to develop strategies around prevention and care.

Knowing a few statistics on HIV and AIDS can help inform us and those who know little to nothing about HIV. Just be sure you interpret the information correctly and check other resources for clarifying data. Being familiar with the aforementioned websites can keep you in touch with all the most current HIV/AIDS epidemiological information. Staying informed on all the numbers is crucial in understanding the tragedy and the achievement that is AIDS.

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This article was provided by Positively Aware. It is a part of the publication Positively Aware. Visit Positively Aware's website to find out more about the publication.
See Also
More on HIV Treatment in the Developing World


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