The US government has recommended near-universal testing for the Aids virus, saying too many people are missed by the practice of focusing on people who seem to be at high risk.
Nearly everyone aged from 13 to 64 would be screened under the new proposals issued by the US Centers for Disease Control and Prevention (CDC). Pregnant women would get extra screening to ensure they do not pass the virus on to their baby.
HIV, which causes Aids, infects more than one million people in the US, and the CDC estimates that 40,000 people become infected every year. But many do not realise it because HIV causes mild symptoms at first, quietly destroying the immune system over time. "We urgently need new approaches to reach the 250,000 Americans with HIV who do not realise they are infected," said CDC director Dr Julie Gerberding.
"People with HIV have a right to know that they are infected so they can seek treatment and take steps to protect themselves and their partners."
Infected people risk passing Aids on to partners, their babies and in blood or shared needles. A cocktail of drugs, now available in single once or twice-a-day pills, can keep patients healthy, and using condoms reduces the risk of passing it on to partners.
Current US guidelines call for people considered at high risk to get tested for the virus. But Dr Bernard Branson, who is in charge of laboratory diagnostics at CDC, said doctors were not always good at guessing who might be at high risk. People were often reluctant to admit to high-risk behaviour, such as drug use or anal sex, even to their doctors.
"Our goal is to ensure that everyone who receives medical care also has the opportunity to learn if they are infected with HIV," said Dr Kevin Fenton, director of CDC's national centre for HIV, STD and TB prevention.
"Making the HIV test a normal part of care for all Americans is also an important step toward removing the stigma still associated with testing."
The American Academy of HIV Medicine said it was important to allow patients to opt out of the test easily.