Anal tests to detect coronavirus: what are they like, what is their effectiveness and in which cases are they used?

The detection of the coronavirus has become one of the main pillars in combating the pandemic. Serological tests, antigen tests, or PCR  are some of the tests that have been talked about until now. However, now a new method has been unveiled:  anal testing.

A few days ago, the news that the growing pressure to control the outbreaks has led  China to include anal tests among the conditions for people arriving from abroad to the cities of Beijing and Qingdao has caused a reaction both in the media and in social networks. According to the state newspaper  Global Times, both the capital of the country and that of the eastern province of Shandong is requiring this method as part of the quarantine requirements.

That is why many now wonder if this type of test is really necessary,  taking into account that the most common methods have proven to be effective, if it is going to arrive in Spain or if it will be a regular test.

What do these tests consist of?

This is a test similar to PCR, the only difference being the area where the samples are taken. While the nasal test collects them from the pharynx, the anal test consists of the introduction of a cotton swab into the rectum, after which it is rotated and removed for processing, explains Dr. Rafael Cantón, spokesman for the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC).

According to the Chinese authorities,  the test lasts only 10 seconds. Despite what it may seem,  "it is not necessarily uncomfortable," according to Cantón, who notes that it is not pleasant, but neither are the other types of screening tests.

What is its effectiveness? Is better?

Quoted by  Global Times, the director of the Clinical Center for Public Health at Fudan University (Shanghai), Lu Hongzhou, assured that anal tests are  "more stable and accurate"  than those of the nose and throat, in which it is more likely taking unusable samples or giving wrong results.

But, although the experts cited by the local Chinese media indicate that these tests would be more accurate than those used so far, Dr. Cantón points out that the sensitivity is similar to the nasopharyngeal ones. However, one of the main differences would be the maintenance of positivity, since in rectal samples it is longer, something that can be both an advantage and a disadvantage. 

"In a low-prevalence scenario, detecting positives - regardless of whether the virus is viable or not -  expands the ability to detect other individuals who have already been positive and may have been asymptomatic. That is, it would allow investigating possible contacts in the chain of contagions, "he says. 

This could have been the strategy adopted in China, taking into account the information released by the local media. But Cantón recalls: "You have to interpret the tests well because they  can be positive  for a longer time  without the need for viable viruses ."

It's something new?

Despite what it may seem,  this alternative is not new.  From the beginning of the pandemic, the different and possible locations in which to apply the tests were studied in order to establish the detection strategy, and "it was seen that it could be adequate," explains Cantón.

Something that sources from the Servizo Galego de Saúde (Sergas), after the latest news that indicated that this method had begun to be used in Galicia: "It has been applied since the beginning of the pandemic, without any change of recent procedure ". "In Galicia, most of the sampling is through the nasopharyngeal route, but the anal is a modality that has already been implemented for specific cases," they add.

In fact, anal tests had already been used in Shanghai in early 2020  as one of the standards to authorize discharges to hospitalized COVID-19 patients, although after a while they were discontinued.

Cantón ensures that in Spain this is an ordinary screening test,  but rare since it is only applied in specific situations. " It is also used for other studies, such as intestinal parasites, or for the control of multi-resistant bacteria that colonize patients when they are admitted," recalls the SEIMC spokesperson.

In what cases are they recommended to be used?

Both Sergas and the SEIMC have indicated that rectal tests are performed on seriously hospitalized people  "with a high compromise of the airways or who have, for example, mechanical ventilation" and in which they try to avoid the spread of the coronavirus, as well as in newborns or in patients with "little collaboration"  or in "agitated situation".

At the moment, in  China, they are applied exceptionally in specific groups of people who are considered to be at high risk of contagion,  since they are not feasible for mass tests.

But, according to the state newspaper  Global Times,  in recent weeks, in the face of the worst outbreaks registered since mid-2020, some cities - such as Beijing and Qingdao - have used this method to check suspicious cases and for routine checks on-chain workers. cold, a sector that the Chinese capital has in its sights as one of the possible culprits for the latest wave of infections.