The way COVID-19 has spread in local clusters, onboard Diamond Princess and in a church in Korea, has opened questions about its contagiousness.

1. It is a droplet infection: Passes through droplets from coughing or sneezing. When these droplets carrying the virus from an infected person reach the nose, eyes, or mouth of another person, they can transmit the virus.
2. High viremia in early illness.
3. It is infectious in both URTI and LRTI stage: Respiratory illnesses can be segregated into two categories: upper respiratory infections - involving the nose, pharynx, or larynx (common cold and seasonal influenza); and lower respiratory illnesses - like pneumonia, which affect the lungs.  

The original 2003 SARS virus was a lower respiratory infection: It replicated in the cells within the lungs and caused pneumonia. People also appeared to spread the virus days into their illness. Thus it was more difficult to transmit SARS to others and the task of containing the virus became easier.

COVID-19 appears to be a different. While it can also lead to pneumonia, by replicating in the lung cells, it can replicate in the upper respiratory tract as well, even when people don’t have any symptoms or just begin to feel sick.

In a paper published in the New England Journal of Medicine, German researchers isolated the virus from patients’ upper respiratory tract even before they began to show any symptoms. This provides additional evidence for asymptomatic spread of the virus from the nose and throat.

4. The virus might also spread through feces: In a paper from the Chinese Center for Disease Control and Prevention, researchers could isolate live virus from stool samples of COVID-19 patients.

This suggests that the disease could spread when there’s suboptimal hygiene. China CDC has therefore recommended measures to stop the spread of the virus through this route. The advice includes: maintaining environmental health and personal hygiene; drinking boiled water, avoiding raw food consumption, and implementing separate meal systems in epidemic areas; frequently washing hands and disinfecting surfaces of objects in households, toilets, public places, and transportation vehicles; and disinfecting the excreta and environment of patients in medical facilities to prevent water and food contamination from patients’ stool samples.

More research is needed to understand the significance of fecal-oral route in the spread of this disease.

5. Airborne transmission: During the first SARS outbreak, a large Hong Kong housing estate became ground zero when more than 300 people were infected with the disease through airborne transmission.

Such a condition arises when the residue from evaporated, virus-containing droplets gets suspended in the air and goes on to infect those who breathe it in. This is not droplet transmission, since droplets are too large to float through the air and need to be sprayed directly on someone’s eye, nose, or mouth in order to infect them.

In this particular case of transmission, it was later found that SARS was capable of going airborne, spreading through the building’s faulty plumbing and ventilation systems to the people who lived on the estate.

Vito Iacoviello, chief of the vision of infectious diseases at Mount Auburn Hospital in Cambridge, Massachusetts, has noted that the US Centers for Disease Control and Prevention is recommending people admitted with COVID-19 to be put in an airborne isolation room. That is the precaution used for TB, measles, and chickenpox.

6. The super spreader: The R0 value of the individual may be more that the R0 value of the virus or the person has more viruses than the others. It has been seen that an HIV-positive person sheds less virus than HIV + STI-positive person. We may need to find out the additional factor which intensifies the spread.
7. Contact period: The virus may survive on the surface longer than thought. Similar viruses have been surviving for up to a week. 

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA