Sarah Baron, Harold Pierce, Dirk Baron, and Tabea Mahler
COVID-19 disease took the public health system and shined a bright light on the terms, practices and history. Every day numbers and rates fill our news feeds, and we are bombarded with shifting messages and projections. This blog will explain some terminology and then answer these questions: what do these numbers mean, why are these strategies in place, and why are public health professionals, journalists and the world watching these numbers daily?
Public health professionals watch for outbreaks
Just like firefighters may watch for a blaze to spark in a forest to control its spread, public health professionals are always on alert to watch for disease outbreaks. In fact, outbreaks occur annually, monthly and even daily across communities all over the world. On a daily basis, health departments and professionals are monitoring diseases to look for outbreaks. For the public health, the key idea is to prevent an outbreak before it spreads and this requires vigilance and dedication.
The key terms for watching a disease grow are:
- Endemic: a health condition that appears at a steady rate in a geographic area or among a population.
- Outbreak: when the condition occurs above the typical endemic levels.
- Epidemic: when the outbreak spreads to larger areas.
- Pandemic: when the condition has spread globally.
With COVID-19 this disease moved quickly from an outbreak to an epidemic and now is a pandemic. This is not the world’s first pandemic, however. Public health agencies keep close records on past pandemics to determine what has worked in containing a pandemic. See the history of pandemics in the US here - the history of responses.
Who is in charge? Good Question. There are many people in charge...
In the United States, the public health system has different levels of key players, each with a specific role and limited power.
Two important points:
- The power to implement public health mandates lies with the local government and States. If you get the feeling that State and Federal governments have different approaches to this pandemic and mandates, this is why...they do.
- The second point is this division of power, is supported by the constitution and is open to interpretation. The 10th amendment allows policing power to be held by the States in certain circumstances.
Why public health people watch them closely
There are three big tenets to public health:
- Protecting the health of entire populations.
- Preventing problems from happening before people get sick or injured.
- Promoting healthcare equity, quality and accessibility.
Why are there different numbers at different times of the day?
The data is collected at the local level, then reported to the State level and then in real time uploaded to the Center for Disease control. This is why you see a shift in numbers throughout the day. It depends on when you look at the data and where it was collected. The most up-to-date numbers are at the local health departments or State labs who are tracking cases in real time and then uploading the data in real time to CDC. These cases needed to be considered confirmed and verified prior to publishing the results. Depending on when and where you look, these numbers will shift throughout the day.
Pay attention to how the data is presented. It tells different stories.
- Linear Scale - this watches the number of cases each day and in a pandemic it shows a steepening line once the disease suddenly increases. This is called an Epi-Curve.
- Epi-Curve- this is a tool to monitor outbreaks (see CDC tutorial here)
- Log Scale -Why use this scale? Infectious diseases don’t spread in an even, linear fashion but a log scale shows exponential growth. It takes out the daily cases and has us focus on the growth and/or if it is declining. The scale is set to grow by a factor of 10. This allows us to see when cases take a jump exponentially. Often you will see trend lines in the graphs, which help show the rate of growth.
- Rate- an expression of the relative frequency with which an event occurs among a defined population per unit of time, calculated as the number of new cases or deaths during a specified period divided by either person-time or the average (midinterval) population. (see CDC Principles of Epi for definitions). Rates are used to compare populations to see who is impacted more than another population. In public health we use rates to look at health disparities. See example here of health disparity story on COVID 19.
- Testing data varies by area along with the lab response time. This is why it is important to pay attention to the log scale data which tunes out the small ups and downs and allows you to focus on the rate of growth. Go to this website for the growth rate in your county.
- For when we discuss rates next week- Week 3 see this excel spread sheet with rates. The source is Rachel Alexander, Salem Reporter Journalist who is downloading data from OHA
- The last slide provides favorite data links.
- On the screen, you will need to move the cursor to see the full slide with notes.