Anchor
General

What does a positive COVID-19 test result mean?

 , ,

What does a positive COVID-19 test result mean?

I would like to provide context on what a positive (or negative) COVID-19 test result means.

In short, for low prevalence diseases, there are high false positive rates.

Without getting too much into the weeds, I came across this great interactive website demonstrating the biostatistics behind COVID19 testing.

The fact is, we do not know the prevalence (how many people have COVID-19 in the population at any moment). How many people have the virus changes how we interpret positive and negative test results.

The higher the prevalence, the more people who have COVID-19 at any one time, the more likely a positive test result is a true positive and not a false positive. This is called Positive Predictive Value (PPV).

Using published sensitivity and specificity from a real COVID-19 Rapid Antigen test, I calculated the PPV for 4 scenarios with different prevalence:

  • Testing in Florida has consisted of those with symptoms, exposure to people with COVID-19, retesting to assure recovery, and those with concerns for COVID-19. This increases the likelihood of a positive result. The positive rate of this population is 8%. I used this as a high prevalence rate.
  • The estimated COVID-19 prevalence in Miami is 6% – the highest in the state. This is a more realistic high prevalence rate.
  • I also ran 3% and 1% prevalence rate scenarios as I suspect those are closer to real numbers for the state.

What I found:

  • If you have a negative COVID-19 test result in any of these scenarios, you can be more than 99.99% sure you do not have COVID-19!
  • If you live in Miami and have a positive COVID-19 test result, you only have a 50.3% chance of truly having COVID-19! There is a 49% False Positive rate for that estimated prevalence!
  • For the state of Florida, I think the overall prevalence is 1-3%. Anyone in Florida with a positive COVID-19 test, the overall likelihood you really are infected by COVID-19 is somewhere between 13-33%!
Social Media

So Many COVID-19 Models and Predictions

 ,
There are many models being discussed right now with attempts to predict what will happen with the COVID-19 pandemic.
 
I urge you to be cautious with COVID-19 projections.
 
Every model begins with assumptions. Any error or unexpected variation in these assumptions builds on the other assumptions (and their errors/variations) and results in potentially inaccurate conclusions for many of these models.
 
Instead:
  1. Take (common sense) appropriate actions to minimize risk
    1. Social distancing
    2. Hand washing
    3. No face touching
    4. Disinfecting high-touch surfaces)
  2. Feel free to listen to the possible model outcomes, but avoid thinking of them as a certainty.
What ends up happening will depend entirely on how we, as a society, react to this disease.
  • Take it seriously
  • Do the actions to not put yourself or your family at risk
General, Outreach

Answers to Frequent COVID-19 Questions

 ,

A Letter I Sent To My Patients This Week

Friends,

As I write this, we have had 1,171 COVID-19 positive cases in Florida so far. As a global community, we need to work together as a unified team to stop this pandemic as fast as possible. Building on my last email, I want to provide some answers to some common questions I have been asked by my patients:

How contagious is this virus?

Remember: Without contact with someone who has COVID-19, you cannot get it.

This virus is quite contagious and continues to spread. While quite contagious, it is spread by droplets and is not aerosolized. This means you will not likely get it by simply standing next to someone with it, walking past someone, or even touching them. You cannot become infected with this virus through your skin.

Were that infected person standing or walking by you cough or sneeze in the air and you breathe those droplets in, you can get infected. Should you shake the hand they coughed into, or doorknob they touched and then itch your eye, nose, or mouth, you can get infected.

The contagiousness of a disease is often expressed scientifically in a notation called R0. The R0 for COVID-19 is estimated around 2-3 right now (there are many variations on this estimate). This means that right now 1 person infects around 2-3 other people.

For comparison’s sake, here are some other diseases and their R0:

  • COVID-19: 2-3 (estimated)
  • HIV: 3.6-3.7
  • Seasonal Flu: 1.3
  • Measles: 11-18

This demonstrates the need for social distancing, hand washing, and avoidance of touching your face. Again, without contact with someone who has COVID-19, you cannot get it.

What are the symptoms of COVID-19?

COVID-19 symptoms overlap with other common seasonal conditions. These include Influenza (currently still prevalent), seasonal allergies (pollen counts are HIGH in Central Florida), and other viral colds.

As a member of a Direct Primary Care office, you have the luxury of reaching out any time you feel concerned. Please do not hesitate to call, text, or e-mail me with any questions about potential symptoms. I am happy to discuss these with you.

Symptoms for this virus begin 2-14 days after exposure. The most common symptoms are:

  • Fever (over 100.5 F) – Most patients have fever.
  • Cough
  • Shortness of breath

Should more severe symptoms occur, call 911 and explain concern for potential COVID-19. These severe symptoms include:

  • Trouble breathing
  • Persistent pain or pressure in the chest
  • New confusion or inability to arouse
  • Bluish lips or face

How do I avoid getting it?

AVOIDANCE! Remember: Without contact with someone who has COVID-19, you cannot get it.

All strategies revolve around avoidance of potential exposure to the virus.

  • Practice good hygiene:
    • Wash your hands (for at least 20 sec) frequently
    • Avoid touching your face
    • Cough or sneeze into a tissue or the inside of your elbow
    • Disinfect frequently used items and “high touch” surfaces as much as possible (Your phone is very dirty!)
  • Work or study from home
  • Avoid social gatherings, especially if there are 10 or more people
  • Avoid discretionary travel, shopping, and social visits

Avoid spreading this virus to those at high risk:

  • Do not visit nursing homes, retirement homes, or long-term care facilities. One nursing home facility in Washington suffered 26 deaths when COVID-19 was transmitted there.

People of all ages can become infected with COVID-19. While those who are younger are less likely to experience severe episodes, they can easily spread the disease to others who are higher risk. Working together to contain the spread of this virus is important for all of us.

Am I a high risk person?

If you are an older person and/or have a chronic health condition, stay home and away from other people.

Those who are higher risk should they become infected with COVID-19 are:

  • People aged 65 years and older
  • People of any age with excess weight with a body mass index (BMI) over 40
  • People with chronic lung disease or moderate to severe asthma
  • People who have heart disease with complications
  • People who are immunocompromised including cancer treatment
  • People who live in a nursing homes or long-term care facilities
  • People with underlying medical conditions like diabetes, kidney disease, or liver disease

If I get infected, what is the treatment?

It is important to remember that most people can be safely treated at home (81% of all COVID-19 positive cases according to one study). Current hospitalization rate in Florida is less than 20%.

There is no vaccine nor specific antiviral medication for COVID-19. Management mostly consists of treating symptoms and avoiding further exposure to others.

Symptomatic treatment includes assuring sufficient fluid hydration, cough suppression with dextromethorphan, zinc supplementation, and acetaminophen for muscle aches/joint pains.

If you are infected, avoid spreading COVID-19 to others.

  • Wear a mask – face masks will not protect you from COVID-19, but will help prevent the spread of the disease to others
  • If you feel sick, stay home. Do not go to work.
  • If your children are sick, keep them home.
  • If someone in your household tests positive, keep the entire household at home.

Have you heard about the caution regarding using ibuprofen?

This idea came from a French report based on some anecdotes. The evidence against its use is very weak. At this time, I think there is not enough evidence to say ibuprofen will result in worse disease process. If you have specific concerns, please reach out.

What about these other treatment modalities like hydroxy-chloroquine?

There are several medications currently being studied for effectiveness. There are some moving stories being reported in the news as well. These are all promising and provide glimmers of hope. I urge caution on placing too much weight on these treatment modalities until they are tested further.

I am aware of 3 potential vaccines in development, 4 different antivirals, and 4 medications from the biologics class with potential to treat COVID-19 and improve outcomes. As you are able, avoid the expectation for a rapid cure and instead concentrate your efforts on prevention.

How do I get tested?

First, think: Should you be tested?

The testing criteria are pretty strict. Not everyone needs or should be tested.

Here are the current CDC recommendations for testing (and what I and other Central Florida doctors are following):

  • If you have symptoms of acute lower respiratory illness (e.g., fever, cough, and shortness of breath) AND meet one or more of the following criteria:
  • Have had a close contact with a laboratory-confirmed COVID-19 case.
  • Are hospitalized with acute lower respiratory illness of unknown origin.
  • Have a history of travel to or from an affected geographic area with widespread community transmission.
  • Have traveled internationally or been on a cruise.
  • Are over 65 with chronic health conditions.
  • Are immunocompromised.

Should you meet these criteria, call the office, and I will order a test for you.

Remember, a positive or negative test does not affect your treatment much unless you develop severe symptoms.

If you feel sick, whether it is COVID-19, the flu, or any other cold, you should stay home, avoid other people, wash your hands frequently, cover your coughs, and disinfect surfaces. Treatment for most COVID-19 cases (and other colds) are managing symptoms and avoiding getting others sick.

As always, if you have questions, concerns, thoughts, suggestions, or any other comment, please do not hesitate to reach out to me!

Stay healthy,

Dr. Matt