A paper published in a recent issue of the peer-reviewed, open-access journal ‘Emerging Microbes and Infections’ has cautioned that SARS-CoV-2, the virus causing the COVID-19 outbreak , is being shed through multiple routes, so testing through oral swabs alone might not be sufficient.
A paper by Wei Zhang, et al, all from the CAS Key laboratory of Special Pathogens at the Wuhan Institute of Virology, says investigations on patients in a local hospital infected with the virus revealed the presence of SARS-CoV-2 in anal swabs and blood as well. What’s more, more anal swabs than oral swabs tested positive at a later stage of infection. Since COVID-19 is believed to be a disease of the respiratory tract, usually only oral swabs are used for diagnosis, and discharge is based on the oral swabs testing negative. The anal positives suggested, they argued, shedding through the oral-fecal route, and therefore transmission is possible as well. The researchers also showed that a serology test (testing blood for antibodies) can improve detection positive rate, and thus should be used in future.
As part of the research, samples - including oral swabs, anal swabs and blood - were collected by Wuhan Pulmonary Hospital. Two investigations were performed – the paper describes - In the first investigation, samples were taken from 39 patients, 7 of whom were in a ‘severe condition’. In the second investigation, samples were lifted from 139 patients, whose clinical records were not available.
“When counting all swab positives together, we found most of the positives came from oral swab (8/10, 80%) on day 0. However, this trend appears to change on day 5. We found more (6/8, 75%) anal swab positive than oral swab positive (4/8, 50%),” the paper says. The data suggested a shift from more oral positives during early period to more anal positives during later period, it adds.
“We show that the current strategy for the detection of viral RNA in oral swabs used for 2019-nCoV diagnosis is not perfect. The virus may be present in anal swabs or blood of patients when oral swabs detection negative,” the researchers say, indicating the possible gaps in current detection methods. “We detected the virus in oral swabs, anal swabs and blood, thus infected patients can potentially shed this pathogen through respiratory, fecal–oral or body fluid routes.”
This observation implies that a patient cannot be discharged purely based on oral swabs testing negative, and the researchers go on to make a recommendation to do serological tests to confirm status.
