China Introduces Anal Swabbing for COVID-19 Diagnostic Testing

While we've all become familiar with the traditional nose and throat swabs associated with COVID-19 testing, some scientists are looking at a testing option with potentially increased accuracy. Reports have surfaced of a new—although controversial—diagnostic test administered in China: anal swabs.

Anal swabs work by inserting a cotton-tipped swab about 1 to 2 inches into the rectum, which is then sent to a lab to be tested for the virus. These swabs analyzed in the same way as the Polymerase Chain Reaction (PCR) COVID-19 tests taken from the nose or throat.

COVID-19 has been known to cause a range of gastrointestinal (GI) issues such as vomiting, nausea, and diarrhea. And the Centers for Disease Control and Prevention (CDC) says genetic material of SARS-CoV-2, the virus that causes COVID-19, has been detected in the blood and stool.

A study published in the February issue of the journal Gut found that even in the absence of GI issues, stool samples in patients remained positive for viral infection. Evidence of viral infection in the stool was still observed even after the virus was cleared from the lungs. Now, in an effort to control outbreaks, China is turning to this testing method as a more accurate way of curbing the spread of the virus.

Is Anal Swabbing More Accurate?

Yang Zhanqiu, a deputy director of the pathogen biology department at Wuhan University, told China’s Global Times that the invasive technique is justified because of its superior accuracy to other traditional tests.

Some research suggests anal swabs could be more accurate than nasal or throat swabs. A small August 2020 study published in the journal Future Microbiology found that people tested positive for COVID-19 when an anal swap test was conducted, even when samples from throat swabs and saliva were negative.

However, William Lang, MD, medical director of both WorldClinic and JobSitecare and a former White House physician, tells Verywell that it isn’t so much that anal swabs are more accurate but rather PCR-based throat swabs having “persistent positives.”

When people are infected with COVID-19, their bodies typically get rid of the virus's infectious parts in about 9 days. The CDC currently recommends 10-day isolation for people who test positive for the virus. After the 10-day window—where the virus would be most infectious—Lang says remnants of the virus can still be detected. The CDC estimates a non-replicating coronavirus can stay up to 12 weeks—leading people to continue testing positive even after all symptoms dissipate.

“Data shows that this is even more pronounced in stool, with PCR detection of not-infection-capable particles for over 4 weeks,” Lang says, although he’s doubtful on whether the test is better than traditional methods. “While there is some evidence that anal swabs could pick up [an] infection in situations where nasal or throat swabs are negative, the clinical utility of this would be minimal."

He also says that an anal swab's detection is very sensitive in the later stages of a COVID-19 infection and runs the risk of producing positive results for non-infectious cases. “More detailed studies would be needed to prove the duration and likelihood of persistent positivity in stool, but it is likely that even more people would remain positive after they are no longer infectious," he says.

Invasive Testing May Lead to Lower Turnout

While anal swabbing is more sensitive at detecting SARS-CoV-2, Lang is concerned the invasive produce would deter people from getting tested.

A Weibo, a Chinese social media platform, poll recently reported that 80% of respondents could not accept getting anal swabbed for COVID-19 testing.

“Saliva may not be as sensitive, but if people suspect they may be subjected to anal swab, there is a high likelihood that the rate of testing would go down," Lang says. "No one is going to consider anal swabs for primary screening…the false negative of other PCR is just not high enough to warrant that.”

Lang says nasal swabs will continue to be the gold standard of testing because of their:

• Accessibility
• Convenience
• Reasonable accuracy

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.