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With inputs from Dr Monica Vasudev
1043: RT-PCR can be redetected but not re-positive
- A positive real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) antigen test is highly accurate, pointing to the presence of SARS-CoV-2 RNA.
- There seems to be no significant cross-reactivity with other respiratory viruses or other coronaviruses.
- A study from Korea suggests that patients with persistent positive tests, beyond 10 days from the initial positive test, who do not have any symptoms are no longer infectious.
- For patients with a high suspicion of COVID-19, a negative test should not exclude the infection.
- The number of false-negative results is not clearly known, though the resultant risk is high.
- Several factors affect the odds of a false-negative test, such as the time when the sample was collected in relation to the timing of illness and the type of specimen collected.
- Nasopharyngeal swabs are likely more accurate compared to nasal or throat specimens.
- Repeat or serial testing enhances the sensitivity; however, it may not always be available.
- rRT-PCR is the current standard, yet, more inclusive consensus-based criteria would possibly be introduced due to the concern about false-negative results.
- Patients who are discharged from isolation after recovery and who again test positive for SARS-CoV-2 are not likely to be infective, suggests a report from the Korea Centers for Disease Control and Prevention (KCDC).
- Theres no relapse.
- The disease is known to linger and to affect more than one system of the body. But, other viral diseases, such as influenza and mononucleosis, also work the sameway.
- As of May 15, researchers in Korea had identified 447 patients who tested positive again on RT-PCR testing for viral RNA. Of these, 63.8% patients had undergone epidemiologic investigation and contact investigation. Of those tested, 59.6% were tested for screening purposes, and 37.5% were tested as they had symptoms. About 44.7% of the 284 patients who underwent investigation were symptomatic.
- Data obtained from three groups of patients from different cities revealed that 25.9%-48.9% of the patients again tested positive after discharge.
- Among the 226 symptomatic patients, when their case was initially confirmed, a repeat positive test result after discharge was noted an average of 44.9 days from the date of initial symptom onset. The average duration from the time of discharge to the time of the second positive test was14.3 days.
- Nearly 60% of patients who tested positive a second time underwent a test for screening purposes, irrespective symptoms. Of those who again tested positive, 44.7% had symptoms such as cough and sore throat.
- In order to ascertain if a positive result on a second test was associated with infectivity, researchers assessed 790 contacts of the 285 patients who tested positive a second time. Of these, 351 were family members, and 439 were others. Among the contacts, three new cases were detected. But for these three patients, other sources of infection were possible, including religious groups or family groups in which there were persons who were confirmed to have COVID-19.
- The researchers tried to culture virus from 108 patients who tested positive a second time; all such cultures were negative.
- First and second serum samples were obtained from 23 patients who had tested positive a second time. About 96% of these tested positive for neutralizing antibodies.
- Active monitoring, epidemiological investigation, and laboratory testing of re-positive cases and their contacts showed no evidence to indicate infectivity of re-positive cases.
- Patients who have been discharged from isolation do not require further testing and are not likely to be infective, despite again testing positive on RT-PCR assay.
- The patients will no longer be considered as ‘re-positive cases’ but as ‘PCR re-detected after discharge from isolation.’
Dr KK Aggarwal
President CMAAO, HCFI and Past National President IMA