Epidemics: Definition

00:00 Hello, my name is Dr. Raywat Deonandan and thank you for watching my videos on infectious disease pandemic epidemiology.

00:10 In this video, we'll learn how to define epidemic and pandemic.

00:14 We'll look at the different kinds of epidemics, some of the famous epidemics going back throughout history, going back hundreds of years.

00:22 We'll look at some of the methods of transmission of these diseases.

00:27 And finally we'll go over some of the ways we can control transmission.

00:31 I hope you enjoy them.

00:34 With this course, we hope that you'll have a few objectives for your learning.

00:38 First, you're going to know how outbreaks, epidemics and pandemics are defined and how you can classify epidemics according to how they spread through a population.

00:49 You're going to be able to name at least one pandemic in each of the following time periods: the 1900s, The 1800s and after 2000.

00:59 you're going to learn a lot about zoonotic diseases and be able to name one from the following categories: bacteria, viruses, fungi and parasites.

01:09 And you want to learn about some of the important indicators for describing epidemics and pandemics particularly the CFR, the case fatality rate and the IFR, the infection fatality rate.

01:21 You're going to be able to calculate some of the important indicators as well, such as the primary and secondary attack rate.

01:28 And you're going to do so by looking at some original data.

01:33 You're going to learn about some other important monitoring indicators, Things like the R-nought, the basic reproduction number, herd immunity and how we calculate the herd immunity threshold from the R-nought.

01:45 You're also going to learn how the effective reproduction number R, Or R sub e is different from R-nought.

01:53 You're going to compute R-nought from original data and you're going to know what factors affect its value and how to use this indicator to predict the evolution of an epidemic.

02:03 I'm going to show you how to draw the graphs of two diseases with the same R-nought but one being more infectious over a short period of time and the other being less infectious.

02:13 And how, using that graphical technique can help us understand how the disease is spreading.

02:20 You're going to learn how to interpret various types of epidemic curves and even be able to construct one from your own data.

02:29 And you're going to identify the main components of a disease transmission cycle.

02:34 And using that information, be able to devise infection control methods for interrupting that cycle.

02:41 We're going to learn a little bit about some of the infectious disease models, like the SIR/SEIR and the basic assumptions and faults that underlie all models.

02:53 And lastly, we're going to talk about the major challenges of the pandemic of the day, COVID-19.

03:01 So let's start with defining some terms.

03:04 First is 'outbreak'.

03:06 What's an outbreak? You've heard this term.

03:08 Public health officials always talk about outbreaks.

03:11 An outbreak is an increase, often a sudden increase in the number of cases of a disease above what is normally expected in that population in that particular area.

03:22 Now what is normally expected is going to vary from place to place, and different people are going to have different thresholds.

03:28 So it's very much a qualitative distinction.

03:31 But we use the word outbreak to describe a sudden appearance of the disease.

03:36 An epidemic is a lot like an outbreak, But we usually use that word to define outbreaks affecting many people over a wider area.

03:46 Again, it's a more qualitative distinction between the two.

03:49 And lastly pandemic, that's the big one.

03:52 That's an epidemic that spread over several countries or continents or official WHO regions and that affects a large percentage of the population.

04:02 Pandemic is typically worldwide.

04:05 So, outbreak is the smallest type of disease manifestation.

04:12 Epidemic is the medium type, and of course pandemic is the largest one.

04:17 It's important to realize that these distinctions do not are not based on the severity of the disease, but just on the degree to which it's spreading.

04:29 So the official definition of an epidemic from the CDC, is that epidemics occur when an agent and susceptible hosts are present in adequate numbers and the agent can be effectively conveyed from a source to the susceptible hosts.

04:43 Okay, what did I just describe there? I described an infectious disease.

04:48 An agent is the disease, the pathogen.

04:51 The hosts are the people who become infected, and the agent is being conveyed between the source to hosts.

05:00 What I described there is the spread of an epidemic.