COVID 19 Challenges: Why at some places it is more contagious
Dr KK Aggarwal
President CMAAO, HCFI and Past National President IMA
The way covid 19 has spread in local clusters in diamond princess and a church in Korea has opened questions about its contagiousness.
1. It’s a droplet infection: Pass through droplets from coughing or sneezing. When these virus-laden droplets from an infected person reach the nose, eyes, or mouth of another, they can transmit the virus.
2. High viremia in early illness
3. Its infectious in both URI and LRTI stage: Respiratory illnesses generally fall into two categories: upper respiratory — infections in the nose, pharynx, or larynx, like the common cold and seasonal influenza; and lower respiratory illnesses, like pneumonia, which infect the lungs.
The original 2003 SARS virus was a lower respiratory infection: It replicated in the cells deep within the lungs and caused the pneumonia. People also seemed to only spread the virus days into their illness, when it was already clear they were sick. This made SARS more difficult to pass on to others and the job of containing it relatively easy.
The Covid-19 disease appears to be a different. While it also can eventually lead to pneumonia, replicating in the lung cells, the virus does a great job of replicating in the upper respiratory tract, even when people don’t have any symptoms or just begin to feel sick.
In a New England Journal of Medicine paper, researchers in Germany were able to isolate the virus from patients’ upper respiratory tract even before they showed any symptoms — more evidence of the potential for asymptomatic spread of the virus from the nose and throat.
4. The virus might spread through feces: In this new paper from the Chinese Center for Disease Control and Prevention, researchers managed to isolate live virus from stool samples of Covid-19 patients. And they’re not the first to find the virus in stool.
As with norovirus, this means the disease could be passed around when there’s less than optimal hygiene. That’s why the China CDC recommended taking measures to stop the spread of the virus this way, including: 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 of 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.
But just because the virus is found in stool doesn’t mean that’s how it’s transmitting. And, again, more research is needed to figure out how important the fecal-oral route is in the spread of this disease.
5. Airborne transmission: One more thing to watch out for: In the first SARS outbreak, a large housing estate in Hong Kong called Amoy Gardens became ground zero of a public health nightmare when more than 300 people were infected with the disease through yet another viral transmission route: airborne transmission.
This happens when the residue from evaporated, virus-containing droplets gets suspended in the air and indirectly infects those who breathe it in. It’s different from droplet transmission, since droplets are too large to float through the air and need to get sprayed directly on someone’s eye, nose, or mouth in order to infect them.
In the case of Amoy Gardens, researchers later learned 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, and an editor at Dynamed, noted that the US Centers for Disease Control and Prevention is recommending people admitted to hospitals with Covid-19 be put in an airborne isolation room. That’s 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 what 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