Covid-19: RT-PCR test errors stump Karnataka

The rise in mysterious cases where patients test negative for RT-PCR but are found to have serious Covid-19 infection through high resolution CT (HRCT) scan has prompted the government to work on a new Standard Operating Procedure (SOP).

This is being done to prevent "false" negative patients from transmitting the infection to others.

So far, the state SOP had treatment protocol for four groups: asymptomatic, mildly symptomatic, moderately and severely symptomatic. Officials have come across patients with lung-related issues who had tested negative for RT-PCR more than once but later turned positive. They estimate that such cases may be less than 5% of the total Covid cases.

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Recently, two staff nurses at Sri Jayadeva Institute of Cardiovascular Sciences and Research (SJICR), who had severe fatigue, tested negative for RT-PCR twice, but a CT scan of their lungs showed typical Covid features.

Dr C N Manjunath, state nodal officer for Covid-19 testing and director of SJICR, said, "The nurses responded to Remdesivir and steroid treatment. They tested positive for Covid later, when the RT-PCR test was conducted for the third time."

Dr Trilok Chandra, member of the State Critical Care Support Unit (CCSU), said, "This scenario has been in clinical discussion since March. Infection could be in the transition zone. If on the first swab, patients have tested negative but are presenting as SARI (Severe Acute Respiratory Infection) cases, we consider them as Covid suspects and treat them on similar lines as Covid patients are."

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An HRCT and X-ray is suggested in such cases. Along with HRCT, tests for inflammatory biomarkers (D-dimer, ferritin, CRP, LDH, IL-6) will also be done. These are tests doctors rely on to assess the severity of Covid.

"A repeat RT-PCR test has to be done with a gap of 48 hours if biomarkers and HRCT are positive for Covid. To make it clear to hospitals, we are including it in the SOP by the end of this weekend. SARI cases by definition are serious enough to be hospitalised. So, they cannot be at home or asymptomatic," Chandra said.

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Dr Anoop Amarnath, Head, Scientific Board and Chairman-Geriatric Medicine, Manipal Hospital, and another member of state CCSU, said, "Data from districts for SARI cases with CT positive and RT-PCR negative stands at less than 5% of total Covid cases. In such cases, although the preliminary RT-PCR is negative, the HRCT shows 'ground-glassing'. In all the cases that we have seen in this condition, invariably the RT-PCR will come positive after 48 hours."

Ground-glass opacity (GGO) is a radiological finding in a CT scan consisting of a hazy opacity that does not obscure the underlying bronchial structures or pulmonary vessels.

This in conjunction with positive biomarkers and clinical symptoms like breathlessness and oxygen requirement going up would make them candidates for Covid treatment.