Coronavirus SARS-CoV-2 is spreading
If you follow the news you’ve probably heard the words “Wuhan” and “Coronavirus” a lot lately. In December 2019 a cluster of
patients was found in Wuhan, China, with pneumonia of unknown cause. The virus has since spread rapidly over the last month there have been over 20,000 confirmed cases according to the World Health Organization. While the majority of the cases remain in China there have been confirmed cases in countries around the world including several in the United States and Australia.
The interim named of the new virus is 2019-rCoV. Coronaviruses derive their name from the crown likespikes that adorn their surface resembling the Sun’s corona. Coronaviruses are zoonotic which means they’re transmitted between animals and people. It remains unclear with the host animal of the new coronaviruses though bats are a prime suspect. Experts think another animal may serve as an intermediate host but they have not identified it yet. During the course of the outbreak a number that you may never have heard of shown up again and again. It’s called the R0 and it’s been a critical part of the scientific effort to understand just how transmissible the new virus is.
Understanding what it is can tell us some useful things about all disease outbreaks. The R0 is also known inside epidemiology as the basic reproduction number. It’s a measure of how potentially infectious that disease is. What that boils down to essentially
is the are not predicts how many additional people one infected person could get sick in a population with no immunity to the disease. In general the higher the R0 the core infectious the disease. And the value of one is important when it comes to the R0. An R0 less than one means the outbreak will peter out, whereas an R0 greater than one means the infection will continue to spread. Here are some R0s from past outbreaks. Measles’s R0 is an estimated 12 to 18. SARS or Sudden Acute Respiratory Syndrome has an R0 of 2 to 4. it is also a coronavirus virus. Early
genetic analysis suggests that the new coronavirus emerged from a virus related to SARS.
Coronavirus (COVID-19) health alert
So what is the R0 of 2019-n-CoV? An early scientific consensus is forming around than R0 of 2 to 3. But the R0 can be thought of as some silver bullet metric for the reality of this outbreak or any other. Infectious disease expert David Fishman of the University of Toronto explains If you didn’t know that an infectious disease and you let it just run through a totally immune population early on in the epidemic how many secondary cases would you get for each primary case that’s what they R0 is it’s right at baseline and the reason people distinguish R0 from the reproduction number later in an epidemic and sometimes called RE which is R effective is that reproduction numbers change for a few different reasons one of them is that people become immune and that deprives the disease of new susceptible people to infect and that slows epidemics down the second thing that changes reproduction numbers pretty predictably and without vaccines or antibiotics or public health care intervention is that people’s behavior often changes in the context of epidemics people react to them sometimes in ways that are helpful in terms of
reproduction numbers and sometimes in ways that are unhelpful.
Cases by source of infection
If the outbreak was tailing off and everybody looks around and says I can come out of hiding now because the outbreak is going away you can have multiple waves of outbreaks so that’s one example behavior changing affecting reproduction number. How do we calculate R0? Well there are a couple of different components to R0. One is how many contacts does the case have per unit time. One is how likely are they if they’re infected to infect each of those contacts so probability of transmission conditional on contact and then the third component
of R0 is duration of infectivity. So the longer your infectious the more people you can potentially infect and that drives the reproduction number up. It’s a unitless quantity so you need to rescale the epidemic into into bug time rather than people time and we call that the serial interval, which is you can you can use our knot to map out what an epidemic is likely to do if you know what the serial interval is.
And that’s the average interval between a becoming infectious and that case’s average secondary case becoming infectious. That’s how we talk about generations and infectious diseases. So you use R0 in combination with serial intervals to figure out how diseases are going to grow. One of the frustrating things about a situation like this where everyone’s sort of on edge and wants it to stop and go away is the time steps in this epidemic are seven or eight days so people look at change in case numbers day to day that has nothing to do with the underlying
epidemic that has to do with how many people are getting tested.
So we really don’t see the contour of the epidemic play out at one to two day time stamps. It’s week to week to week so patience is the watchword and I feel like you make predictions on this stuff at your peril. As the total number of covid 19 cases reported worldwide rises, there are many media outlets reporting vaccines acquired by various governments. Naturally, as death tolls increase in the aged populations, contact tracing and virus testing becomes much more prominent.
Stay tuned to the information services in your state or province for the latest updates from the government public health resources. If you have symptoms or covid 19 coronavirus medical questions locate your nearest hospital to get tested.