Negative test results do not prove the absence of COVID-19 – time standard

If it is positive, you can be convinced that the COVID-19 infection is active, but a negative COVID-19 test result is not necessarily an infectious disease.

The test used at the Humboldt County Institute of Public Health (New Coronavirus Real-Time Reverse Transcription Polymerase Chain Reaction Diagnostic Panel of the Centers for Disease Control and Management 2019) is very specific, detecting targets and others Almost never. , And very sensitive to detect small amounts of that substance. In this case, it happens to be the viral genetic code.

“It’s really one of the gold standards,” said Dr. Teresa Francovich, director of health at Humboldt County, in a video on Wednesday.

Currently, the polymerase chain reaction (PCR) test is the most widely used test for detecting the virus that causes COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2). Video by Dr. Carmen Wiley, President of the American Society of Clinical Chemistry.

“When a patient’s sample has only a small amount of virus, PCR can get the genetic material from the virus and target specific gene segments that only the virus has, making very many copies of those segments.” They can be detected and measured, “Wiley said.

The CDC test is specifically targeted to SARS-Cov-2, so if positive in those without a disease test, it can cross-react with another genetically similar coronavirus, resulting in a false positive result There is almost no sex.

The same cannot be said about false negatives if the sick person is negative.

“Negative results do not rule out 2019-nCov infections and should not be used as the sole basis for treatment or other patient management decisions,” the CDC’s instructions on test status.

False-negative results can occur for a variety of reasons, including when and where the virus is collected in the body because the virus is below the detection limit.

In a preliminary study of 1,070 samples collected from 205 Chinese COVID-19 patients, the sample size was 8 swabs, while nasal swabs had a 63% positive rate, but respiratory samples had the highest positive rate. It is “SARS-CoV-2 in Different Types of Clinical Specimens” was published on March 11, in a peer-reviewed journal of the American Medical Association.

Studies show that bronchoalveolar lavage fluid collected from the lungs has a 93% chance of being virus tested positive, and sputum, or sputum, has a 72% positive rate. The positive rate in other parts of the body was much lower, for example 1% in blood and 0 in urine.

Currently, the CDC recommends using a hypopharyngeal swab to test COVID-19. This requires “increasing technical skills and equipment needs” for the collection of samples from the lower respiratory tract and should only be done for those who present with serious symptoms, as directed by the authorities on collection and handling. That’s why the sample.

Samples collected from the upper respiratory tract have different positive rates depending on how infected a person is, according to “Time course of the false negative rate of the reverse transcriptase polymerase chain reaction-based SARS-Cov-2 test” .. It was published in “Annals of Internal Medicine” on May 13th.

In a literature review, “the probability of false-negative results in infected individuals was reduced from 100% to 4% on day 1 to 67%.” “The median false-negative rate on the day of symptom onset was 38%,” “On day 8, it dropped to 20% and on day 9 it started to rise again from 21% to 66%,” the review says.

“Testing will tell you the status of the day,” says Frankovich. “It really doesn’t tell us anything about your status for the next day or the next day.”

In addition to positive test results, health authorities are looking at other factors such as COVID-19, for example, type of symptoms and known contacts of those who test positive. ..

Francovich said that if there were no symptoms, having more than one test every two weeks would not help.

“But if you develop mild symptoms, even if it’s a short period of time, get involved and have a test,” Francovich said. “If you see more serious symptoms, please contact your provider.”

You can contact Sonia Waraich at 707-441-0506.