CLEVELAND — Every day at 2 p.m., the Ohio Department of Health updates several COVID-19 statistics to give the people of Ohio an understanding of the impact of the disease on the state’s populace. One of the most closely watched numbers is the number of new cases each day, and one question that comes up consistently in response to our reporting on those numbers is: does the number of COVID-19 cases in Ohio include antibody tests?
Well, yes and no. It’s complicated. Here’s as simple of an explanation as we can provide.
Antibody test versus viral test
First, what is an antibody test, and how is it different from the nasal or throat swab test?
Antibody testing, also called serologic testing, is typically performed on a blood sample, and, ideally, shows whether you have ever been infected with the virus in the past. The test checks for antibodies that appear in the blood between one to three weeks after COVID-19 symptom onset and may remain as long as a lifetime. It is not yet known whether these antibodies protect against reinfection with the virus, as they do with some other virus types.
Antibody tests, however, are notoriously unreliable, with the CDC saying late last month that nearly one-half of antibody tests may be inaccurate.
“Serologic test results should not be used to make decisions about grouping persons residing in or being admitted to congregate settings, such as schools, dormitories, or correctional facilities,” the CDC stated in May.
Viral testing, performed on nasal swabs or throat swabs, tests for the presence of the virus itself, and if positive, means the patient most likely currently has an active COVID-19 infection that can be spread to others. A negative test means the person most likely does not currently have an active COVID-19 infection.
So, as the CDC explains, the most simple way to view the results of each test is:
Viral test positive: Most likely* you DO currently have an active COVID-19 infection and can give the virus to others.
Viral test negative: Most likely* you DO NOT currently have an active COVID-19 infection.
Antibody test positive: You likely* have HAD a COVID-19 infection.
Antibody test negative: You likely* NEVER HAD (or have not yet developed antibodies to) COVID-19 infection.
The CDC included this important caveat in its guidance for interpreting test results: “No test is ever perfect. All tests occasionally result in false positive results (the test result should be negative because you DO NOT have COVID-19 but comes back positive) or false negative results (the test result should be positive because you DO have COVID-19, but comes back negative). Sometimes the results are not definitive (the result is unclear, and you don’t know if it is positive or negative). For this and other reasons, results should always be reviewed by a healthcare professional.”
Does Ohio count antibody tests in its reporting?
Well, hold on. We’re not there yet. First, it must be understood that the Ohio Department of Health releases three different case numbers each day: probable cases, confirmed cases and total cases.
Cases are considered confirmed by the ODH when a patient’s viral test comes back positive, indicating that they do currently have an active COVID-19 infection.
Probable cases are cases that meet some criteria but have not been confirmed by a viral test.
The total cases are a combination of the confirmed and probable cases and includes both cases confirmed by a viral test and cases that meet the CDC definition of probable.
According to the CDC, there are three ways a case is considered probable:
- A person meeting clinical criteria AND epidemiologic evidence with no confirmatory laboratory testing performed for COVID-19;
- A person meeting presumptive laboratory evidence AND either clinical criteria OR epidemiologic evidence;
- A person meeting vital records criteria with no confirmatory laboratory testing performed for COVID-19.
To break that down further, “clinical criteria” are defined as:
At least two of the following symptoms: fever (measured or subjective), chills, rigors, myalgia, headache, sore throat, new olfactory and taste disorder(s)
At least one of the following symptoms: cough, shortness of breath, or difficulty breathing
Severe respiratory illness with at least one of the following:
· Clinical or radiographic evidence of pneumonia, OR
· Acute respiratory distress syndrome (ARDS).
No alternative more likely diagnosis
Epidemiological evidence or linkages are defined by the CDC as:
One or more of the following exposures in the 14 days before onset of symptoms:
· Close contact** with a confirmed or probable case of COVID-19 disease; OR
· Close contact** with a person with:
clinically compatible illness AND
linkage to a confirmed case of COVID-19 disease.
· Travel to or residence in an area with sustained, ongoing community transmission of SARS-CoV-2.
· Member of a risk cohort as defined by public health authorities during an outbreak.
The CDC says presumptive laboratory evidence includes:
· Detection of specific antigen in a clinical specimen
· Detection of specific antibody in serum, plasma, or whole blood indicative of a new or recent infection*
Finally, vital records criteria is just a death certificate that lists COVID-19 as a cause of death or a significant condition contributing to death.
Therefore, in order for a case to be considered probable without an antibody or viral test, the patient would need to display either one or two symptoms and have had some kind of documented exposure to a person or areas associated with the disease.
Even with a positive antibody result, the CDC still requires an additional piece of evidence, either a clinical symptom or symptoms, or evidence of exposure, before it is considered a probable case.
So, for real, does Ohio count antibody tests in its reporting?
Yes – antibody tests are counted among the probable cases reported by the ODH but not the confirmed cases, according to ODH Press Secretary Melanie Amato.
“Probable can be antibody testing, or cases that have yet to be confirmed,” she said. “For example, they meet the case definition but are waiting on their tests. Antibody tests will always remain probable.”
This is in accordance with CDC guidelines for reporting COVID-19.
The reporting of probable cases was established in April after a statement was issued by the Council of State and Territorial Epidemiologists, which made COVID-19 a nationally notifiable disease. Because the disease is so new (hence novel coronavirus), and because the disease was spreading so widely in the U.S., and because there needed to be a standardized surveillance method to recognize and understand the transmission of the disease, that group and the CDC decided to include probable cases in the data it published and recommended state and local jurisdictions track as well.
Therefore, looking at the probable cases, and the number of total cases, gives an indication of the locations and scope of COVID-19 infections. It is not intended to be the final number of total actual COVID-19 infections.
However, as has always been the case, confirmed cases do not include antibody tests. If you’re looking for hard numbers on how many people actually have or had COVID-19, the number of confirmed cases will always be the most accurate number.
Didn't you say you were going to explain this simply?
If you're looking at the probable cases or total cases, they will include antibody tests. But, for a case to be probable, it also requires another piece of evidence - such as symptoms or evidence of exposure to another person with COVID-19.
If you want to see just cases where the person had a positive viral test and almost certainly has the disease, you'll want to look at the confirmed cases number on the state's website.