Explained: Can throat-nose swab test rule out coronavirus? A study in The Lancet, a case in Mumbai

Can a person have coronavirus in their body even if their respiratory samples test negative?




A death review committee set up by Brihanmumbai Municipal Corporation (BMC) will assess the cause of death of the 68-year-old Philippines national who passed away in a private hospital in Mumbai on Sunday night. The man was initially admitted to the BMC-run Kasturba Hospital. Days before his death, he had tested negative for SARS-CoV-2, the virus from the coronavirus family that causes COVID-19.

The BMC committee will assess whether he died of COVID-19, or renal failure with acute respiratory distress syndrome (ARDS).

What is the history of this case?

The man was part of a group of nine Philippines nationals who arrived in Mumbai on March 3. He then took a train to New Delhi, and returned to Mumbai on March 10. On March 12 afternoon, he developed symptoms of flu, and was taken to a local doctor. On March 13, he tested positive for COVID-19, and was admitted to Kasturba Hospital.

With co-morbidities like diabetes and asthma, his condition remained critical, and he was put on ventilator support. In between, he developed kidney complications, and was taken to the BMC’s B Y L Nair Hospital for dialysis. He was tested in accordance with protocol and, a few days ago, his nasopharyngeal swab (swab taken from the back of the nose and throat) tested negative for the novel coronavirus.

The man was then discharged, and was shifted to a private superspecialty hospital for treatment of his kidneys. This is where he died. Dr Daksha Shah, BMC’s deputy executive health officer, said that since the man had tested negative, his death is so far not being considered a COVID-19 death.

Why must the case be studied further?

The key question is: Is a nasal or throat swab sufficient to rule out the virus? That is, can a person have the virus in their body even if their respiratory samples test negative?

A new study in The Lancet Gastroenterology and Hepatology shows that the novel coronavirus can remain in the faeces of patients for five weeks after their respiratory samples test negative. (‘Prolonged presence of SARS-CoV-2 viral RNA in faecal samples’, Yongjian Wu et al.: published March 19, https://doi.org/10.1016/S2468-1253(20)30083-2)

The researchers analysed respiratory and faecal matter of 74 COVID-19 patients from January 16 to March 15 at the Fifth Affiliated Hospital of Sun Yat-sen University in Zhuhai, China. In 55% of cases (41 of 74 patients), the respiratory samples (throat swabs) tested positive for coronavirus for 16.7 days, and faecal matter tested positive for 27.9 days after the first onset of symptoms, the study found.

The implication is this: Even if a confirmed case returns negative for the novel coronavirus in a nasal swab test, the virus may still be in body.

What does this finding mean in the context of the 68-year-old Filipino?

That there is a possibility that he may have still had the virus in his body fluids, even though his respiratory samples tested negative. Given his age, asthma, diabetes, and later renal complications, the virus added to the problem and worsened his condition.

The Lancet study found that the virus was “actively replicating in the patients’ gastrointestinal tract” even after clearance from their respiratory tract. It also said that there is a possibility of viral shedding for nearly five weeks in the faeces of infected person. The virus could remain in the environment for days, and could be transmitted by the faecal-oral transmission mode, although this is yet to been detected in a COVID-19 case.

Similar transmission patterns were observed during the Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) outbreaks, both of which were caused by pathogens of the coronavirus family. Dr Om Srivastava, an infectious diseases expert who is a member of the death review committee, said: “Further tests are needed to check viral load in saliva, tears, semen as well. Zika virus remained in semen for nine months.”
Blood, urine, and stool samples of confirmed COVID-19 patients at Kasturba Hospital are being sent every day to the National Institute of Virology in Pune for analysis of viral shedding.

What will the BMC’s panel do now?

A member of the committee said that stool, urine, and blood samples of the Philippines national will be analysed to test for the presence of the virus, and whether viral shedding continued after he was discharged from Kasturba Hospital. The committee comprises infectious disease experts, intensive medicine doctors, and civic health officials.
BMC has earlier taken a similar approach in deaths caused by dengue and H1N1 infection as well. In deaths of patients with several co-morbidities, a review of the medical condition is done to understand whether the infection was the direct or indirect cause of death.

The first COVID-19 death in Maharashtra, a 64-year-old who had travelled to Dubai, too had tested negative for coronavirus a day before his death. He was still considered a COVID-19 death because he passed away before a second confirmatory test for the virus could be carried out. As per government guidelines, two tests must be conducted within 24 hours to rule out the presence of the virus in an infected person.

In the case of the 68-year-old Filipino, both these tests were carried out before the presence of the virus was ruled out.

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