Divergent Covid-19 Test Results in a Patient – Explanation

On the morning of 2nd July, the Ministry of Health (MOH) confirmed that the test results of the Indonesian patient initially thought to have contracted Covid-19 were in fact negative. Negative results were also found in all of the individuals he was in contact with during this time.

On the 30th June, 2020, the patient visited Family Practice Clinic in District 2 to undergo a test for Covid-19 for fly to Indonesia. As the clinic is not eligible to test for this condition, the specimen was sent to FV Hospital, which has been approved by the MOH to perform COVID-19 testing.

After finding a partially positive result (finding specific genes of SARS Covid-19 but not all, specifically the genes N and RdRP with weak titers), at 6pm on the same day, FV Hospital reported this information to Family Medical Practice and to the Health Control Centre of HCMC (HCDC) and sent the sample to the Tropical Disease Hospital for double-check as per requested by HCDC.

The incubation period of Covid-19 is usually 4 to 5 days with extreme between two days and two weeks. Because there hasn’t been any community case of the disease in Vietnam for more than 2 months and because this patient entered Vietnam early March and hasn’t left since, the possibility of him being infected by Covid was extremely improbable.

Pasteur Institute looked for the gene E which was absent and correctly concluded that the patient was not infected. Later on, a serology came back positive for IgG antibodies which means that the patient was most probably infected long ago.

How was this possible? It comes down to the fact that PCR detects viral RNA, which can be present in fragments of the virus, and does not distinguish between infectious virus and non-infectious nucleic acid (RNA).

It has been shown and published ( that viral shedding in Covid-19 can persist quite a long time after the infection is healed. However viral shedding does not mean infectivity. Infectivity is due to the shedding of complete, “live” virus, and is demonstrated by viral culture. In patients with viral shedding detected after the infection has healed viral cultures are negative.

The explanation is that the immune system neutralises viruses by lysing their envelope or aggregating virus particles, these processes prevent subsequent infection but do not eliminate nucleic acid (RNA), which degrades slowly over time.

For many viral diseases (SARS, MERS, influenza, Ebola, Zika and more) it is well known that viral RNA can be detected long after the disappearance of infectious virus. With measles virus, viral RNA can still be detected 6–8 weeks after the clearance of infectious virus. With Covid-19 prolonged shedding of RNA occurs and does not mean that the patient is contagious

We hope that this effectively clarifies the story.

FV Hospital would also like to state that, contrarily to what was published by some, the patient never came to the hospital which only receive the test sample, and as soon as the partial positive test was discovered both Family Medical Practice and FV Hospital collaborated with the HCDC and the patient was immediately placed in isolation until more testing results were available