Hi friends. Wow. How are you? I took over a week off of blogging to, much like most of the rest of the world, adjust to my new normal due to the novel coronavirus. If you’re anything like me, you might be finding it hard to focus on tasks like work and schoolwork, as the news is all-engrossing, ever-changing, and at times, very overwhelming. I plan to go back to posting content about non-coronavirus things soon, but before I do, I thought I would make a handy reference list of some common public health definitions to help you understand COVID-19 news.
These phrases are all over that the news these days, so I hope this post helps you understand what they mean, so that you can perhaps better comprehend what’s going on in the world right now.
I’m not an infectious disease epidemiologist or doctor, but I was introduced to many of these phrases during my MPH. Yay for public health.
Read on for some public health definitions for COVID-19 (and public health in general) that are being used by public health experts and journalists to discuss updates of the novel coronavirus.
Also, I didn’t really add photos to this piece. Usually, I add a lot of photos. But I didn’t have any original photos that I felt really made sense here, so I stuck to infographics I made, instead. Feel free to scroll through them!
Epidemiology is a data-driven, systematic scientific discipline. It is the study of distribution (frequency, patterns) and determinants (causes, and risk factors) in specific populations (communities, or individuals viewed collectively) and the application of this study to control health problems. It deals with collecting, analyzing, and interpreting data on health and disease. It is sometimes described as the ‘basic science’ of public health.
An epidemic refers to a condition that affects a large proportion of individuals within a population, community, or region at the same time. An example would be the Zika virus.
A pandemic is the worldwide spread of a new disease that impacts an exceptionally high proportion of the population.
The phrase ‘endemic’ refers to the baseline level of a disease in a population. It is not necessarily the desired level of the disease in a population (which may be zero), but rather, the baseline or actual amount.
A disease is considered to be endemic when it is maintained at a baseline level in in geographic area. Influenza is considered endemic, as it is predictable to reoccur every year. Some have expressed concern that COVID-19 may become endemic, meaning it comes back repeatedly over time.
A hyperendemic is persistent, high levels of disease.
An influenza pandemic occurs when a new virus emerges and spreads around the world. Most people do not have immunity to pandemics, which is part of why they are able to spread so much.
Immunity refers to the development of a state of resistance against an infectious agent. Right now, because COVID-19 has never before been transferred to humans, no one had immunity to the disease, which is part of why it is spreading so quickly.
Typically, people develop immunity to a disease via a vaccine or by contracting the disease and developing antibodies (or your body’s defense system) against it. Currently, there is no vaccine for COVID-19. Post-infection immunity to COVID-19 is not completely defined; however, it seems as though most similar viruses lead to post-infection immunity.
Also known as community immunity or population immunity, herd immunity occurs when a high percentage of a community is immune to a contagious disease. People may become immune to some diseases through vaccination, and/or previous illness from the disease.
When a high enough percentage of the population is immune to the disease, the rest of the population is far less likely to get the disease, because far less people are carrying the disease around infecting others.
Herd immunity is why vaccines work on the population level. Even those who can’t get vaccinated (whether they are immunocompromised or ill), are far less likely to get a disease when most of the people they interact with can’t get or spread the disease.
Generally speaking, the more infectious a disease is, the greater the percentage of immunity within the population is required for herd immunity. Once a certain threshold of the population acquires herd immunity, a disease can be eradicated (meaning, it’s effectively eliminated)from the population.
An asymptomatic or healthy carrier is an individual who does not show any clinically recognisable signs or symptoms of an illness, but is still hosting or carrying around a disease agent, possibly transmitting it to other people.
Part of the concern with COVID-19 is that about 80% of the infections appear to be mild, meaning there are many barely or asymptomatic carriers of the disease increasing its spread.
Previous viruses, like SARS and MERS, were easier to contain because people did not spread the disease until they were symptomatic, making it much easier to isolate people who could give the disease to others. COVID-19 is stealth in transmission, which is why it is so hard to contain.
Flatten the curve:
“Flattening the curve” is a concept from infectious disease epidemiology. It refers to slowing the spread of an infectious disease to spread out cases of illness over a longer period of time, with the intention of preventing lots of people from getting sick at the same time, in hopes of not overwhelming the health care system.
Flattening the curve has been talked about a lot with the COVID-19 outbreak. Flattening the curve via strict social distancing is indeed essential to public health, as it can help people get adequate treatment when they need it (versus being turned away due to hospitals being at capacity).
However, there is concern about whether or not the strict social distancing practices being seen now are sustainable long-term, and if outbreaks will spike again once social distancing regulations are relaxed. For now, we will have to watch and wait to see what happens when countries begin to relax regulations.
An outbreak typically refers to something similar to an epidemic (meaning a condition that affects a large proportion of individuals within a population, community, or region at the same time), but usually in a smaller area than an epidemic.
A cluster is an aggregation of cases in a place and time that is typically greater than the number that would be expected.
Community spread refers to a disease being spread within an area, and some people are not sure of how or where they became infected. In the COVID-19 context, community spread refers to spread within a population where infected people did not have any history of traveling to impacted areas.
The incubation period is the amount of time from when a person is exposed to the causative agent (disease or vector) until the first symptoms develop. The typical incubation period for COVID-19 is 1-14 days, with a median (meaning most often reported) incubation period of 5 days. This means that a person may be exposed to the virus, and it will take anywhere from 1 day to 2 weeks for them to show symptoms characteristic of the disease.
The latent period is the time period from infection to onset of ability to be infect others.
The mortality rate is a measure of frequency of occurrence of deaths in a population during a specific time interval.
The formula for mortality rate is below:
10^n refers to the conversion factor, meaning it helps you gauge the amount of people you compare your rate to. For example, if n=3, 10^3 = 1000, meaning you wound calculate your mortality rate per 1000 people.
Basic reproductive number (R0):
You may have seen R0 mentioned in news articles. It refers to the basic reproductive number, which can be thought of as the expected number of cases generated by one case in the population where all individuals are susceptible to infection, meaning, it assumes that all other individuals are not infected nor do they have immunity towards the disease.
The R0 for COVID-19 is estimated to be between 2.06-2.58.This means, every person who gets COVID-19 will infect roughly 2-2.58 other people. For reference, the basic reproductive number for influenza is approximately 1.3.
Generally speaking, in epidemiology, if R0 = 1, the number of cases is stable. If >1, the number of cases is increasing, and if <1, it means the number of cases is decreasing.
Case fatality rate:
Case fatality rate is an epidemiology term that refers to the proportion of persons with a particular condition (cases) who die from the condition.
The formula for case fatality rate is as follows:
The value is a proportion. For example, if 100 people have the flu and 3 of those people die from influenza, the case fatality rate would be (3/100)*100 = 3%.
COVID-19 has an estimated case fatality of 0.8-4.2% (the exact value is currently unknown; as more data emerges we will be able to have a more accurate value). For reference, influenza has a case fatality rate of 0.1%
Also known as direct transmission, contagion means transmission of an infection from one individual to another.
PPE stands for personal protective equipment worn to minimize exposures to hazards in a workplace. This phrase can mean different things in different contexts (for example, doctors have different PPE than do construction workers). In the COVID-19 context, PPE typically refers to N-95 (fitted, specially protective) face masks, and certain eye protection, gloves, etc.
Well, that is all for now. I hope you found this article about public health definitions for COVID-19 (and public health in general) to be useful in some way, or to help you better understand what’s going on in the world right now.
Have a great day! Millie loves you.
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Public Health Definitions for COVID-19, 2020.