One-fourth of all new HIV cases in the United States occur in people under age 21, a development that many observers attribute to the false sense of security created by the success of antiretroviral drugs in treating the disease and by feelings of invincibility leading to risky behaviors, the Virginian-Pilot reports. Medical advances to prevent mother-to-child HIV transmission have virtually eliminated prenatal cases, and people infected in such a manner often live into their teens or 20s due to antiretroviral treatment. The Norfolk, Va.-based Children's Hospital of The King's Daughters estimates that it is treating at least twice the number of HIV-positive teens that it treated 10 years ago. Many young people who contracted HIV prenatally have had experience with an HIV-positive parent who has died or had a serious illness as a result of the disease, which often encourages teens to maintain the complicated AIDS drug regimen. However, teens who do not have such a "touchstone" often have difficulty adhering to treatment, a problem compounded by teens' tendency to lead "chaotic lives. Shun authority. Keep secrets. And wear defiance like a badge of courage," according to the Virginian-Pilot. Erratic adherence to a drug regimen can be dangerous, as such behavior can prompt the development of drug resistance, and each time resistance develops, a teen must switch to a different antiretroviral regimen (Simpson, Virginian-Pilot, 4/6).