Can a person test negative and later test positive for COVID-19?

Viral tests are performed to determine whether an infection is currently present. A negative result indicates that the COVID-19-causing virus was not detected in the individual’s sample. This indicates that the individual is likely not infected with the coronavirus. False negatives can occur for several reasons, including people being tested too soon after exposure to the virus (which may not allow enough time for the virus to build up to a detectable level). Differences in how well the coronavirus replicates in one person versus another. And instances where sample collection (e.g., swabbing) does not capture enough of the virus for whatever reason.

In one study. Johns Hopkins concluded that negative COVID-19 PCR tests conducted 3 to 5 days after exposure could not be relied on to determine infection status; instead, the clinical and epidemiologic situation should be thoroughly assessed by medical professionals. In addition. The study revealed that the false-negative rate is at its lowest point eight days after exposure.

Suppose people believe they have been exposed to COVID-19. In that case. They should isolate themselves, see a healthcare practitioner determine when they should be tested. Or take other measures to address their health and monitor their symptoms.

A negative COVID-19 test result for a sample acquired from a symptomatic individual suggests that the COVID-19 virus is not causing their current sickness.

You are seated next to a person infected with the coronavirus. As they exhale and you inhale. A portion of their virus particles attach to the cells that line your nose and upper airways and begin to enter. Nonetheless, if you were to perform a PCR test at this point, you would certainly test negative. Why?

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At the onset of every viral infection, including COVID-19. There is a period known as the “latent period” during which the infected individual cannot spread the virus. In addition, there is a period known as the “incubation period” before symptoms appear. The degree of overlap is dependent on the virus. Those infected with Ebola. For example, exhibit symptoms before becoming infectious, whereas those infected with COVID-19 typically become infectious before developing symptoms. And many individuals never develop symptoms. This makes it so difficult to contain COVID-19; the most effective intervention (quarantine) is sometimes implemented too late because people are unaware that they are infectious due to a delay in the development of symptoms. The usual incubation time for COVID-19 is 5 to 6 days (but it can last up to 14 days), and researchers believe that persons become infected 2 to 3 days before exhibiting symptoms.

The precise timing of these events is determined by the rate at which the virus replicates in infected cells and whether these cells are involved in the transmission of the virus to other people, as well as the amount of virus the individual was initially exposed to, how they were exposed, their biological susceptibility to that type of virus, and their immune system.

Similar variables may influence when individuals begin to test positive for the virus using diagnostic techniques such as PCR or lateral flow.

Diagnostic delay

SARS-CoV-2 prefers to infect cells lining the airways, with the nose being the most common site of infection. Once within these cells, the virus releases genetic material known as RNA, which the host cell converts into proteins, assembles into new viral particles, and then releases. These viral particles subsequently infect new cells lining the airways, eventually increasing the amount of virus in the body (viral load) and the amount exhaled by an infected individual.

PCR tests begin to detect RNA from SARS-CoV-2 approximately 1-3 days before the onset of symptoms, corresponding to when persons become infectious, with the maximum viral loads found during the first few days of symptoms (assuming the person is symptomatic). From this point on, the amount of virus steadily decreases until it is no longer detectable using PCR. In general, asymptomatic individuals may test positive for 1 to 2 weeks. Whereas those with the mild-to-moderate disease may continue to test positive for a week or longer.

Less sensitive lateral flow or fast antigen tests necessitate a greater viral load to provide a positive result. Which is why they typically only identify individuals during their most infectious phase.

False negatives

While PCR tests are commonly recognized as the gold standard for diagnosing SARS-CoV-2. They are not perfect, and the likelihood of detecting an infection varies depending on the timing of the test. A PCR test performed to confirm a coronavirus infection in an individual who has just acquired COVID-19-like symptoms is more likely to identify the presence of viral RNA than a test performed on an individual who was infected the day before or weeks earlier.

The care with which samples were gathered from the nose and throat may also affect the likelihood that an infected person may test negative (a false negative), with home tests likely less reliable than those performed by professionals.

The UK Government believes that PCR testing should never produce more than 5 percent false positives. Or 5 percent false negatives in laboratory settings. However, investigations conducted under real-world situations imply that false negatives are more prevalent.

In a recent study, Chinese researchers attempted to contact all close contacts of persons who tested positive for COVID-19. But who themselves tested negative and urged them to take an antibody test. The data revealed that the PCR tests overlooked 48 (36 percent) of 134 affected close contacts. The scientists said, “Even thorough [PCR testing] techniques may miss a large number of SARS-CoV-2 infections, possibly because of problems in finding the appropriate testing period in asymptomatic people.” Despite these testing limitations, the authors stated that the entire control effort (which included tight isolation measures after exposure) successfully prevented the virus’s spread.

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