America's teens and young adults are at far higher risk for carrying the Human Immunodeficiency Virus (HIV) and spreading it to others than the general population. Yet, too many of them don't even know they are infected. As a result, about 50% of adolescents and young adults with HIV remain undiagnosed.

Untreated, HIV can progress over time from causing no symptoms at all to a full-blown acquired immunodeficiency syndrome (AIDS) leading to complex lifelong illness or premature death.

Many adolescents are concerned about confidentiality. They don't want their parents to find out, through health care bills and notifications from insurance companies, that they are being tested for a sexually transmitted disease.

These undiagnosed teens and young adults can unwittingly contribute to the spread of the virus by transmitting the disease during unprotected intercourse. They are also not getting the early treatment and ongoing health surveillance they need to prevent their infection from progressing to AIDS with its many, often terminal consequences.

Despite public health campaigns and advisories from the Centers for Disease Control and Prevention (CDC) and other organizations that everyone from age 13 to 64 be screened for HIV, fewer teens and young adults are being tested now than they were several years ago.

Researchers looked at HIV testing among two groups. They surveyed about 14,000 sexually active students in grades 9 through 12 each year from 2005 through 2013. And they looked at HIV testing rates for young adults aged 18-24, from 2011 to 2013, following another 22,000 participants per year.

The prevalence of HIV testing was low among high school students (25%) and young adults (33%). And there has been no increase in testing among males and decreased testing among young adult black females even though they are at higher risk of HIV infection.

Despite public health campaigns and changes in guidelines, the rate at which either age group was tested has not increased over time. Worse, between 2011 and 2013, screening among young adult females decreased by as much as 10%.

Why aren't adolescents and young adults being tested? The researchers offered some ideas.

One problem is that many teens and young adults lack access to any health care, including HIV prevention and treatment services. And too few know they should be getting screened regularly.

In addition, many adolescents are concerned about confidentiality issues don't want their parents to find out, through health care bills and notifications from insurance companies, that they are being tested for a sexually transmitted disease.

The authors suggest a multifaceted approach targeting the general public, the teen and young adult population, and health care providers. Kids need adolescent-friendly clinics; providers need education in regard to the concerns of young adults, especially about confidentiality. Finally, improved access to health care will go a long way to addressing the needs of teens and young adults who have HIV infection in the U.S.

The study is published in Pediatrics.