Nose and throat swabs are standard in the US, but the new swab test might be more accurate, according to some experts.

By Claire Gillespie
January 29, 2021
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After localized COVID-19 outbreaks in parts of China, including the capital city Beijing, authorities there have started using anal swabs to test for the virus instead of the usual nose and throat swabs. The reason for the switch? Anal swabs might be better at detecting the virus, some experts believe.

According to state broadcaster CCTV, anal swab testing has been conducted mainly on people living in areas with confirmed COVID cases and those who have been quarantined. Passengers arriving in Beijing and a group of more than 1,000 school children and teachers who were thought to have been exposed to the virus are among the people who've undergone anal swabbing, according to Forbes.

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?

Some experts in China say the anal swab method is a more accurate way of testing for COVID-19 because traces of the virus linger longer in the anus than in the respiratory tract. Li Tongzeng, a senior doctor from Beiking's Youan hospital, told CCTV that an anal swab "can increase the detection rate of infected people."

Anal swabs have actually been used in China to detect the coronavirus since last year, primarily in key groups at quarantine centers. However, CCTV said anal swabs wouldn't be used as widely as other methods, purely because the technique is "not convenient."

"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," Tongzeng said. "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. If we conduct anal swabs for nucleic acid testing, it would increase the detection rates of patients and lower the chance of a missed diagnosis."

A city official in Weinan, in northern Shaanxi province, referred to the case of a 52-year-old man whose symptoms included coughing. The man, who was confined to a centralized facility for medical observation due to being a close contact of another COVID-19 patient earlier in January, initially tested negative for coronavirus. But he was subsequently tested via an anal swab and confirmed to have the virus, the city official told a news conference, as reported by Al Jazeera.

Using anal swabs to detect COVID-19 remains controversial. 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.

But there is some research to support anal swabbing for COVID-19—in children, at least. A paper published in September 2020 by researchers at the Chinese University of Hong Kong (CUHK) found that stool tests may be more effective than respiratory tests in identifying COVID-19 infections in children and infants because they carry a higher viral load in their stool than adults.

The drawbacks of anal swabbing

To date, there's no word about whether US officials will consider using anal swab tests to detect coronavirus; nose and throat swabs are the mainstay here. The practice also has its drawbacks. Infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells 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.

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

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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