2 million COVID-19 cases in the world: Here is what linear and exponential growth mean in the context of an outbreak

The first case of COVID-19 was reported to the World Health Organisation (WHO) in December 2019. Today, only three and a half months later, over two million people have been confirmed positive of the disease in the world so far, according to Worldometer’s data. The epicentre of the disease has moved from China to Europe and the USA. While the latter two are still trying to contain the number of cases — the total number of cases in Italy has crossed 160,000, while there are about 600,000 cases in the USA alone — China has already started opening up Wuhan, the city where the pandemic began. Over the course of these months, various models and estimates have been proposed, explaining how far the number of cases and deaths in the world or in specific countries may go. For example, a projection recently said India may see about 13 lakh cases by mid-May.   [caption id=“attachment_8250631” align=“alignleft” width=“380”]  Representational image. Image by Pete Linforth from Pixabay.[/caption] Here is what they mean by a linear and exponential growth in the context of an outbreak.

Growth curves of infectious diseases

Generally, any population — whether it is of a microorganism or any other living thing — will grow exponentially when they have unlimited resources and soon as the resources start to decline the population will decline too. In the case of an infectious microbe, one of the resources is the presence of a susceptible population.   Even when there is one infected person in a large population, the microbe can spread rapidly in the whole population if preventive measures are not put in place quickly and efficiently.   In an epidemic situation, the growth of a microbe is taken to be exponential initially.   The growth curves and the number of cases are estimated based on the time it takes for the microbe to show up in double the number of people than it was initially.   So say the 10 people were initially infected, in the absence of preventive measures — social distancing, hygienic practices, face masks — the growth curve would be based on how much time it takes the virus to show up in 20 people.   In an exponential situation, the growth will be larger and larger with each stage, something like - 10, 20, 40, 80, 160 and so on. This is quite different from a linear growth curve where the cases would increase by the same amount each time - like 10, 20, 30, 40 and so on. So, in short, exponential growth would mean rapid growth (not ideal in this case) whereas linear growth would be a more controlled and slower growth (more ideal in this case).

Flattening the curve

A lot of countries are trying to flatten the COVID-19 curve right now. According to Johns Hopkins University, a flattened curve will look like just that ‘flat’ on a graph. A flatter curve would mean the number of new cases per day in an area are decreasing and the infection is slowly starting to get under control. Flattening the COVID-19 curve is important because a steep curve will quickly overload the capacity of the local healthcare system, which will lead to more number of deaths. This is what happened in Italy. In a flatter curve, the total number of infected people, in the end, might be the same but it takes much longer for the virus to spread to that many people and, as a result, the healthcare system will be able to deal with the disease appropriately and more people will recover.   So far, the measures that have been suggested to flatten the COVID-19 curve include physical distancing and hand and respiratory hygiene. Countries like South Korea and Germany have kept their curve relatively flatter with aggressive testing and isolation of affected cases.   Read our   Tips on how to protect yourself against COVID-19 infection  for more detailed information. Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.