Explainer: When can people transmit the novel coronavirus?

Coronavirus - screening 1-Optimized

Doctors at two independent labs in Munich in Germany isolated infectious virus from the pharynx of patients experiencing mild symptoms. These patients with early symptoms of common cold may be able to transmit the novel coronavirus to other persons, they claim.

The spread of the novel coronavirus in mainland China continues unabated. On February 5, mainland China recorded 3,694 new confirmed cases of novel coronavirus (2019-nCoV) and 73 deaths taking the total number of confirmed cases to 28,018 and deaths to 563. This is second consecutive day when the number of new cases in a day has risen sharply. On February 4, mainland China recorded 3,887 new confirmed cases and 65 deaths.

The Hubei province alone, the epicentre of the outbreak, reported 2,987 new confirmed cases and 70 new deaths on Wednesday. With this the Hubei province so far has 19,665 confirmed cases and 549 deaths.

Which countries/regions outside mainland China have reported novel virus cases?

As on February 5, 28 countries/regions have reported 244 cases of the novel virus.

With 35 cases, Japan has reported the most number of cases. It is closely followed by Singapore with 28 cases; Thailand 25 cases; Hong Kong 21 cases including one death; South Korea 19 cases; Australia 14 cases; Germany and Malaysia 12 cases each; Taiwan, and the U.S 11 cases each; Macau and Vietnam 10 cases each; France 6 cases; UAE 5 cases; Canada 4 cases; India, Philippines (including one death) and UK 3 cases each; Italy and Russia 2 cases each; Nepal, Cambodia, Finland, Sri Lanka, Belgium, Spain, Sweden and Cambodia 1 case each.

How many human-to-human transmissions outside mainland China have been seen so far?

As on February 4, the World Health Organization says 27 cases of human-to-human transmission of the novel coronavirus have been reported from nine countries outside of China.

The first case of human-to-human transmission outside China was reported from Vietnam. It was followed by Japan, Thailand, South Korea, Germany, Singapore and the U.S.

So far, 15 healthcare workers in mainland China have been infected through such transmission. The main route of transmission currently in China is believed to be through human-to-human transmission as the Huanan Seafood Wholesale Market in Wuhan city, which is considered as the source of the virus, was shut down on January 1.

Can the virus be transmitted during the incubation period?

China’s National Health Commission Minister had first warned that the novel virus might be spreading even during the incubation period when symptoms do not show up. Then on January 30, the New England Journal of Medicine (NEJM) reported that a Chinese woman who had shown no sign or symptoms of infection had transmitted the virus to a German during the incubation period, thus confirming what China’s National Health Commission had said.

But the journal Science later reported that The Robert Koch Institute (RKI), the German government’s public health agency, and the Health and Food Safety Authority of the state of Bavaria found out from the Chinese woman that she did have a few symptoms while in Germany. According to Science, she “felt tired, suffered from muscle pain, and took paracetamol, a fever-lowering medication”.

So it was not a case of a person transmitting the virus during the incubation period, as the letter in NEJM pointed out.

What is WHO’s position on virus transmission during the incubation period?

WHO’s Situation Report posted on February 1 says: “WHO is aware of possible transmission of the novel coronavirus from infected people before they developed symptoms. Detailed exposure histories are being taken to better understand the pre-clinical phase of infection and how transmission may have occurred in these few instances.”

It then stresses that “asymptomatic infection may be rare, and transmission from an asymptomatic person is very rare with other coronaviruses, as we have seen with Middle East Respiratory Syndrome (MERS) coronavirus. Thus, transmission from asymptomatic cases is likely not a major driver of transmission.”

The main driver of novel coronavirus transmission is people who exhibit overt symptoms. Such people will spread the virus more readily through coughing and sneezing, WHO says.

The Public Health Agency of Sweden says on its website that scientific evidence on coronavirus causing Severe acute respiratory syndrome (SARS) “does not infect at all during the incubation period. There is therefore much to suggest that similar would also apply to the new coronavirus”.

Can people exhibiting mild symptoms transmit the virus?

Two laboratories have been independently monitoring virus shedding by patients exhibiting few or minor symptoms and being treated in Munich. These patients have “symptoms of common cold rather than viral pneumonia”, the press release says.

The doctors at the two laboratories could isolate the infectious virus from the pharynx (part of the throat). Both laboratories “found signs of viral replication in the pharynx” besides the lungs.

Based on these observations they say that persons who have “mild or early symptoms of common cold (sore throat, signs of sinusitis, feeling unwell without fever) may be able to transmit the novel coronavirus to other persons”.

“Because of the immediate relevance for infection control, the participating institutions have decided to release this information prior to completion of studies and formal scientific publication,” the release says. The observations have not been published in any journal post peer-reviewing. The findings have not been independently verified by other labs, either.

What do people with mild symptoms spreading the virus mean for infection control?

The Chinese woman who infected the German colleague is an example of a person exhibiting mild, non-specific symptoms spreading the virus to others.

If further studies find that some people infected with the virus have only mild symptoms, it would mean that many people might have gone or will go undetected. So the actual number of cases might be higher. More studies are needed to confirm if people with mild, non-specific symptoms might be spreading the virus and infecting others.

Like in the case of Zika virus, can the novel virus be transmitted from the mother to the child (vertical transmission)?

In China, a baby born to a mother who tested positive of the virus was found to have been infected 30 hours after birth.

“This reminds us to pay attention to mother-to-child being a possible route of coronavirus transmission,” chief physician of Wuhan Children Hospital’s neonatal medicine department, Zeng Lingkong, told Reuters.

But it is also possible that the baby was infected after birth probably due to close contact with the mother. No details are yet available to confirm or refute the claim by the Chinese doctor.

It is considered vertical transmission (mother-to-child) if the virus is transmitted from the mother to the foetus, during delivery or from breastfeeding. According to the World Health Organization, there have been no reported cases of vertical transmission in the case of Severe acute Respiratory Syndrome (SARS) or Middle East Respiratory Syndrome (MERS).

According to the New York Times, the hospital disclosed details of a second case involving an infant who was born healthy but got infected 16 days later. The mother and the baby’s nanny were diagnosed with the virus after the baby was born.

Though the median age of patients is between 49 and 56 years, these two cases suggest that even infants can get infected with the novel virus.

Does a negative result mean the person is not infected with the novel coronavirus?

Not always. There have been at least a few instances when people have initially tested negative for the novel coronavirus before being testing positive. It is not clear at what stage of infection were the initial tests and final tests done.

Dr. Li Wenliang, an ophthalmologist in Wuhan, believed to be a whistleblower of the coronavirus outbreak, felt unwell and started coughing after treating a patient who later developed a fever. Dr. Li’s test results came back negative a few times before his infection was confirmed.

Similar cases have been reported from elsewhere. In Canada, a Chinese woman initially tested negative before further tests confirmed infection. In another case in Canada, a student from Wuhan, who was asymptomatic, initially tested negative. A second test confirmed the case as positive. In Japan, a person who returned from Wuhan had symptoms such as fever and coughing but initially tested negative. An additional test discovered the infection, says a February 1 report.

The failure to detect at the first instance could be due to early stage of the infection. “Our testing procedures are evolving and getting more and more precise,” Ontario’s Chief Medical Officer of Health Dr David Williams said in a statement.

Of the 1,155 people tested as on February 6 in India for the novel virus, only three have been found positive. The Ministry of Health and Family Welfare press release of February 6 says all 645 evacuees from Wuhan have tested negative. In addition, 510 samples have been tested by ICMR network laboratories and only three turned positive. All the three people who tested positive are kept in isolation wards in Kerala.

Published in The Hindu on February 6, 2020