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(CNN)The US Centers for Disease Control and Prevention has changed its Covid-19 testing guidelines. The agency no longer recommends testing for most people without symptoms, even if they've been in close contact with someone known to have the virus.
Previously, the CDC said viral testing was appropriate for people with recent or suspected exposure, even if they were asymptomatic.
Here's what the CDC website said previously: "Testing is recommended for all close contacts of persons with SARS-CoV-2 infection. Because of the potential for asymptomatic and pre-symptomatic transmission, it is important that contacts of individuals with SARS-CoV-2 infection be quickly identified and tested."
The CDC changed the site on Monday. Here's what it says now: "If you have been in close contact (within 6 feet) of a person with a COVID-19 infection for at least 15 minutes but do not have symptoms, you do not necessarily need a test unless you are a vulnerable individual or your health care provider or State or local public health officials recommend you take one."
Those who don't have Covid-19 symptoms and haven't been in close contact with someone with a known infection do not need a test, the updated guidelines say.
"Not everyone needs to be tested," the agency's website says. "If you do get tested, you should self-quarantine/isolate at home pending test results and follow the advice of your health care provider or a public health professional."
The CDC guidelines still say people should get tested if they have symptoms and that someone's health care provider "may advise a COVID-19 test."
"It is important to realize that you can be infected and spread the virus but feel well and have no symptoms," the updated CDC site says, noting that local public health officials might request asymptomatic "healthy people" be tested, depending on cases and spread in an area.
In its pandemic planning scenarios, the CDC says its current best estimate is that 40% of infections are asymptomatic and 50% of transmission occur before symptoms occur.
The CDC did not explain the change, and many doctors were puzzled by it.
"I'm concerned that these recommendations suggest someone who has had substantial exposure to a person with Covid-19 now doesn't need to get tested," said Dr. Leana Wen, an emergency physician and public health professor at George Washington University who was previously Baltimore's health commissioner.
"This is key to contact tracing, especially given that up to 50% of all transmission is due to people who do not have symptoms. One wonders why these guidelines were changed -- is it to justify continued deficit of testing?"
A spokesperson at the US Department of Health and Human Services denied the change would affect contact tracing efforts, which most public health officials say is key to any eventual control of the virus. "The updated guidance does not undermine contact tracing or any other types of surveillance testing," the spokesperson said.
HHS said people should consult with their doctors or with local health officials to decide if they need to be tested.
"The guidance fully supports public health surveillance testing, done in a proactive way through federal, state, and local public health officials," the spokesperson said.
