Could a stool test support COVID-19 testing campaigns and be a useful eradication test?
Diagnostic testing for the detection and management of SARS-CoV-2, the respiratory virus responsible for the global COVID-19 pandemic, is evolving at pace. New tests that enable faster virus detection closer to the patient, or have less invasive sampling methods that facilitate the collection of good quality samples for testing, may produce significant benefits for society and the economy.
Currently, tests for Coronavirus fall into one of two categories – 1) tests that identify the presence of the virus during active infection (PCR tests), and 2) tests that identify individuals that have been exposed to, or previously infected by the virus (antibody tests). To date, identifying those individuals with current active infection by PCR testing remains the ‘Gold Standard’ method for acute-phase testing, while antibody testing proves useful for epidemiological applications such as following the spread and monitoring the prevalence of the virus.
When diagnostic tests are used it is important to understand the limitations of both the types of test and the settings in which they are applied. As with many respiratory viruses, successful identification of Coronavirus requires an understanding of the phases of infection i.e. knowledge of which tests should be used on which samples at what time, in order to provide the most accurate results. It has been shown for example that prior to the onset of symptoms, the likelihood of detecting Coronavirus by PCR tests in nasopharyngeal swabs or respiratory tract samples is lower than for those samples collected during the week that follows the onset of symptoms. Additionally, by week 4 PCR tests may become negative again even if individuals remain carriers of the virus.
When highly sensitive and specific tests for Coronavirus are used that are phase-appropriate, testing regimes can help identify Coronavirus and diagnose COVID-19 with a high degree of certainty. But the question remains – when does a COVID-19 positive individual become free from coronavirus?
When an individual receives a Positive Coronavirus test result the current government guidelines require immediate self-isolation for 10 days post-testing for asymptomatic individuals, or, 10 days post symptom onset for symptomatic individuals. This social-restriction policy helps to minimise communicable spread of the disease but there is no current follow-up test available to confirm successful eradication.
The respiratory symptoms resulting from Coronavirus infection are widely known, however Coronavirus has also been shown to infect the gastrointestinal tract with viral RNA being found in stool samples from large percentages of patients with the disease, which seems to increase with disease severity. ACE2, the receptor to the spike protein of SARS-CoV-2, is widely expressed by intestinal enterocytes which could support the infectivity of Coronavirus in the intestines and it has been suggested that gastrointestinal manifestations of coronavirus including loss of appetite, diarrhoea, nausea and vomiting, and abdominal discomfort may occur before the respiratory symptoms appear, and in addition, the virus remains detectable in stools long after respiratory tract samples are negative, therefore resulting in a larger window of opportunity in which to detect and identify the virus.
Whereas it is accepted that coronavirus infection is spread between individuals through aerosol contamination and close contact, as yet there is no conclusive proof that stool from coronavirus positive individuals is contagious.
Stool tests for Coronavirus
Testing patients’ stool samples for Coronavirus may be important not only to help identify COVID-19 individuals that are still infectious, but also to help identify those individuals who have successfully eradicated and are now clear of the virus. Studies have shown that coronavirus RNA can be found in stools up to eleven days after respiratory tract samples test negative. Hence, this may be of crucial importance when it comes to managing patients who have previously tested positive by respiratory swab and been allowed to return from isolation after 10 days.
Stool tests for coronavirus may also help provide differential diagnosis in specific patient groups such as children, or in those with underlying chronic diseases – particularly of the gastrointestinal tract. For example, inflammatory bowel disease (IBD) patients may experience gastrointestinal COVID-19 symptoms that mimic their usual IBD symptoms. Furthermore, if coronavirus is proven to be transmissible by stool, this has implications for updating policies that steer the clinical assessment and management of possible COVID-19 patients, and specifically, may call for updates for current practices concerning e.g. colonoscopies and faecal microbiota transplantation.
Follow-up regimes for COVID-19 patients that include faecal SARS-CoV-2 testing may demonstrate that, once negative, the patient is no longer infectious. This could provide significant benefits and reassurance in patient management, social distancing models and return to work policies.
Non-invasive sample collection
Swab sampling from the throat and nose is well tolerated and straight forward for most individuals, but for others it can be challenging and even traumatic. The reliability of any diagnostic test is underpinned by the quality of the sample provided so it is important to recognise the needs of different patient groups and individuals when it comes to sample collection so that they get the right result first time.
Stool testing offers a simple and convenient solution. Samples can be collected easily in the safety and comfort of the home or care setting – there are no special requirements and it is non-invasive. Stool testing for Coronavirus might therefore provide a more suitable solution for individuals with special needs.
GA-map® COVID-19 Fecal Test Kit
Testing for the presence of coronavirus RNA in stool can be done by using a new, commercially available test kit. The benefit of using a faecal sample is that sample collection is non-invasive and can be done by the individual at home. The GA-map® COVID-19 Fecal Test Kit, available from BIOHIT, is designed to qualitatively detect SARS-CoV-2 RNA in faecal samples and this novel test is now available in the UK.
Find out more about faecal tests for Covid-19: www.biohithealthcare.co.uk/GA-Covid
