Can Anal Swabs Be Used to Test for Coronavirus?

In January of 2021, after localized COVID-19 outbreaks in parts of China, including the capital city Beijing, authorities started using anal swabs to test for the virus instead of the usual nose and throat swabs.

According to state broadcaster CCTV, anal swab testing was conducted mainly on key groups of people living in areas with confirmed COVID cases and those who have been quarantined.

An anal swab test involves inserting a cotton swab 1.2 to 2 inches into the rectum. Once it's there, the swab is gently rotated several times, then removed and placed into a sample container. The entire process only takes about 10 seconds.

Are Anal Swabs Better at Detecting the Coronavirus?

The anal swabs method “can increase the detection rate of infected people” as traces of the virus linger longer in the anus than in the respiratory tract, Li Tong Zeng, a chief physician from Beijing’s Youan hospital, told CCTV.

"We found that some asymptomatic patients tend to recover quickly. It's possible that there will be no trace of the virus in their throat after three to five days," said Tong Zeng. "But the virus lasts longer from the samples taken from the patient's digestive tract and excrement, compared to the ones taken from the respiratory tract."

A 2020 press release from researchers at the Chinese University of Hong Kong (CUHK) found that stool tests may be more effective than respiratory tests in identifying COVID infections in children and infants because they carry a higher viral load in their stool than adults.

A 2021 paper published in BMJ found that gut microbiome is involved in the inflammation of COVID severity, and may possibly affect the immune responses. The researchers suggest that, even after an individual recovers from COVID, the gut microbiota could contribute to persistent symptoms.

In April of 2022, a study by researchers at Stanford Medicine found that people who are infected with SARS-CoV-2 (the virus that causes COVID) can shed viral genetic material in their feces for up to seven months after diagnosis. The study added to mounting evidence that the SARS-CoV-2 virus actively infects the gut.

Should Anal Swabbing Be More Widespread?

Using anal swabs to detect COVID remains controversial. Some researchers have published that anal swabbing is not superior to nasal or throat swabbing as a detection method for the SARS-CoV2 virus.

One article published in 2022 found that, compared to anal swabbing, nasopharyngeal (nose and throat) swabbing was a more sensitive method for detecting SARS-CoV-2 and should remain the "gold standard" for diagnosis.

A study published in BMJ Open Gastroenterology in 2021 found that anal swabbing had low sensitivity for detecting SARS-CoV-2 antigen. The researchers wrote that anal swabbing may not be needed as an additional test and that the nasopharyngeal swab PCR test remains the standard diagnostic test for COVID-19.

Yang Zhanqiu, a deputy director of the pathogen biology department at Wuhan University, told China's Global Times that the nasal and throat swabs remain the most efficient test, since the virus is proven to be contracted through the upper respiratory tract, not the digestive system.

The Drawbacks of Anal Swabbing

Infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, told Health that while it's true that SARS-CoV2 can be found in the gastrointestinal (GI) tract, and sewage surveillance can be useful to understand community prevalence, it's unclear whether anal swabbing of people is a very useful way of detecting contagious people, especially when they're asymptomatic.

Though used for key groups in isolation, Dr. Tong Zeng said the technique of anal swabbing was "not convenient" and so it wouldn't be used as widely, since faster and more convenient methods such as nasal swabbing.

"I also worry that such messages may discourage people from getting tested," added Dr. Adalja. "For most purposes, including screening asymptomatic individuals, nasal or saliva samples are sufficient."

To date, there's no word about whether U.S. officials will consider using anal swab tests to detect coronavirus; nose and throat swabs are the mainstays here.

A Quick Review

As researchers around the world glean more about COVID and the SARS-CoV-2 virus that leads to infection, approaches to diagnosis and treatment of the virus will change.

Anal swabbing was used in China in early 2021 to diagnose COVID-19 but has not been used in other countries to date. While SARS-CoV-2 can be detected in the gut, and may be present in the gut months after infection, researchers do not believe that anal swabbing should replace nasal and throat swabbing as a diagnostic technique.