Many people test negative quickly, PCR test is positive

Ho Chi Minh CityMany people have Covid symptoms but the rapid test is negative, the PCR test is positive, the doctor thinks that it may be due to incorrect self-sampling, leading to false negative or low viral load.

Ms. Hoang Linh 31 years old, exposed to F0 in the company, symptoms of cough, itchy throat, three rapid tests in three consecutive days were still negative, on the evening of the third day, she started to have a fever. She tested PCR, the result was positive, virus concentration (CT) 25. According to the guidelines of the Ministry of Health, the smaller the CT value, the higher the virus concentration; CT≥30 is one of the criteria for F0 to be considered cured. Thus, Ms. Linh’s CT is 25, which is a low level.

“I have had three vaccinations, coughed phlegm in my throat, not tired, PCR test results are clear, so I feel more secure in treatment and psychological comfort than living in anxiety and suspicion of infection,” she shared.

Mr. Quan (33 years old), Mr. Tung (age 31) lives in Thu Duc city, has been exposed to many F0s, eats together. Both rapid tests were negative, symptoms of mild chest tightness, nervousness, positive PCR test results. After 7 days, the symptoms disappeared, the test was negative, no transmission to family members.

Ms. Linh’s PCR test results were positive, 3 previous rapid tests were negative. Photo: Characters provided

Doctor Nguyen Minh Tien, Deputy Director of City Children’s Hospital, explained that people with typical symptoms of Covid-19 but a negative rapid test may be in the incubation period or have been infected but the virus concentration is at a low level. low level. Therefore, Antigen test results false negative, positive PCR test. Some people perform self-collection of rapid test samples incorrectly which may lead to inaccurate test results (false negative when in fact positive).

“Some people have the flu but mistakenly think they have Covid-19 because the symptoms are similar,” said Dr. Tien. People are afraid (leading to palpitations, nervousness) and are more alert when fever, cough or headache, especially when there is an epidemiological factor of exposure to F0.

In addition, studies around the world have come to the conclusion that rapid test less sensitive for Omicron strain than Delta . strain.

Share on ForbesDr. Gerald W. Fischer cited research from the Centers for Disease Control and Prevention (CDC) showing that rate of false negative tests in people with symptomatic Covid is 20%, asymptomatic people is 59%. The PCR test has a lower false negative rate. Earlier Johns Hopkins research also showed that taking samples too early in the early stages of the disease could lead to false results.

In addition, research shows that Some kits are less sensitive to strains of Omicron, especially in the early days of Covid-19. According to preliminary data from a study published on medRxiv, which surveyed more than 700 people, a common test in the US found that more than 95% of people infected with Omicron had a high viral load. However, when the viral load is low, the test kit misses about 35% of infections.

Data at the end of December 2021 from the US Food and Drug Administration (FDA) confirm that the antigen test is still effective for Omicron infections, but the sensitivity has decreased. This announcement is based on research from Emory University, part of the National Institutes of Health, comparing the performance of rapid tests on samples contaminated with two strains of Omicron and Delta.

Bruce Tromberg, director of the National Institute of Bioengineering and Biomedical Imaging of NIH, USA, also said that the rapid test kit for detecting the Omicron variant was inferior to Delta.

In the context that Omicron is gradually dominating in Vietnam, doctors recommend that people with typical Covid symptoms but a negative rapid test also should not be subjective. “These people need to be monitored for 5-7 days, limiting contact with people around,” advised Dr. Even in case the above symptoms are not Covid but flu, it is still advisable to follow 5K measures to avoid spreading to those around, live safely during the pandemic.

Doctor Truong Huu Khanh, consultant of the Department of Neurological Infections, Children’s Hospital 1, advises not to worry too much if you experience common cold symptoms, only suspecting infection when accompanied by symptoms of shortness of breath.

Quan's rapid test result was negative after being exposed to F0, showing symptoms of chest tightness.  Photo.  Characters provided

Quan’s rapid test result was negative after being exposed to F0, showing symptoms of chest tightness. Photo: Characters provided

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