It takes only one positive Covid-19 case to start another wave of community infections if we let our guard down.

I am referring to the imported case who was probably reinfected in India, infectious on return to Singapore and released into the community as he was deemed to be no longer infectious.

Unfortunately he was, and thus infected two others, starting a new cluster.

Any person with a positive PCR, or polymerase chain reaction, swab must be assumed to be infectious and immediately isolated.

The doctors who deemed him as non-infectious were probably misled by two red herrings - the low viral load, and the positive serology test, which tests for antibodies to the virus.

They probably concluded the very low viral load meant he was recovering from infection.

But a low viral load can equally mean an early acute infection before the virus replicates.

In the current situation of multiple variants of the virus, positive serology, or having antibodies to the virus, just means the patient was infected before and does not rule out a new acute infection.

It could very well still be a sub-acute case and the patient could still be infectious, as this case has shown.

To rely on the viral load and positive serology test to release infectious Covid-19 patients imported from overseas is unwise, and I suggest all who test positive for Covid-19 upon entering Singapore be treated as people with acute infection, and be quarantined appropriately until proven otherwise.

We cannot afford to have another reinfected case starting a new wave of Covid-19 in our community.

Lim Boon Hee (Dr)