12 on Scoot flight who tested positive no longer infectious: MOH
As recovered patients, they may continue to shed viral fragments, which may lead to positive tests: MOH
Fourteen passengers on a recent Scoot flight from Singapore tested positive for Covid- 19 after arriving in China.
They were on Scoot flight TR138, which carried 223 passengers bound for Tianjin on Wednesday last week.
Official state media outlet Tianjin Daily reported that six of the 14 passengers were classified as imported cases and the other eight as asymptomatic cases. None had a fever on arrival.
After they tested positive, they were taken to local hospitals, the report added.
Singapore's Health Ministry (MOH) said yesterday that 12 of the 14 cases are recovered workers who lived in migrant worker dormitories, and are deemed not infectious.
Replying to The New Paper's queries, an MOH spokesman said in a statement that the workers may continue to shed viral fragments for weeks or even months after infection, which may lead to positive polymerase chain reaction test results.
"However, there is no evidence to suggest that these remnant viral fragments are infectious, and studies so far have failed to culture viable virus from these patient samples, indicating that these individuals are no longer infectious and are thus safe for travel," she added.
Singapore is also in contact with the Chinese authorities for further information on the remaining two cases, and investigations are ongoing, said MOH.
Scoot said in an earlier statement that the cabin crew and pilots on the flight had been advised to closely monitor their health and will not operate any flights for the next 14 days.
The aircraft has also been thoroughly cleaned and disinfected, Scoot added.
According to Ministry of Manpower guidelines, foreign workers living in dormitories can leave the country if they are from a dormitory cleared of Covid-19 and are not under any quarantine order or stay-home notice.
MOH said Covid-19 patients assessed to be clinically well at Day 21 of the illness are discharged. This is more stringent than the World Health Organisation's guidelines.
This is based on local and international clinical and scientific evidence that shows that viable virus was not found in Covid-19 patients after the second week of illness.
Singapore's discharge criteria have been shared with the Chinese authorities, said MOH.
Dr Asok Kurup, an infectious diseases doctor in private practice, said it is quite common for patients to continue testing positive even after they have recovered.
"Chronic shedding is a known phenomenon across respiratory viruses. For Covid-19, it starts off with a high viral load and this slowly decreases. After Day 11, these are all dead viruses which are no longer infectious," he said.
Another infectious diseases expert, Dr Leong Hoe Nam, added that virus shedding is also common in other viruses such as enterovirus, and that the Covid-19 virus fragments have been known to shed for months.
He said: "We believe that once you have positive antibodies, you have immunity to it. This would render the virus to be non-infectious."
Findings from a position paper released by the National Centre for Infectious Diseases and the Academy of Medicine's Chapter of Infectious Disease Physicians found there was no viable virus when the viral load is low and the virus could not be isolated or cultured after Day 11 of illness.
This conclusion in the paper was based on a multi-centre study of 73 patients here.
Dr Kurup, who chairs the chapter in the academy, said antibody or serology tests can give an indication of the patient's exposure to Covid-19.
A positive serology test typically indicates that the patient has already been infected for about two weeks.
He said: "The antibody test cannot be used to (check if you are still infectious), but it is useful to prove that the patient already has the antibodies. It gives some clarity as to whether you have been infected before."
Dr Kurup added that former patients discharged by MOH do not have to worry about being infectious as they would have gone through the robust discharge process in place here.
He said: "Someone who has recovered and tests positive is different from someone who has never tested positive before getting a positive result."
In a separate development, the Chinese embassy here announced last Friday that all passengers from Singapore will be required, from this Friday, to take a nucleic acid test five days before the flight to ensure they are free of the coronavirus.
They must also declare that, in the last 14 days, they have not had a fever at or above 37.3 deg C, and have not been in contact with patients with a fever or respiratory symptoms, among other things.