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Yes, it is possible. You may test negative if the sample was collected early in your infection and test positive later during this illness. You could also be exposed to COVID-19 after the test and get infected then. Even if you test negative, you still should take steps to protect yourself and others. See Testing for Current Infection for more information.

You should stay home for 14 days after your last contact with a person who has COVID-19.

Rapid tests are most accurate when used by people with COVID-19 symptoms in places with a lot of community spread. Under those conditions, a rapid test produces correct results 80 to 90 per cent of the time, she said.

Some of the at-home antigen tests have an overall sensitivity of roughly 85 percent, which means that they are catching roughly 85 percent of people who are infected with the virus and missing 15 percent.

Rapid diagnostic tests (RDT) detect the presence of viral proteins (antigens) expressed by the COVID-19 virus in a sample from the respiratory tract of a person.

If the target antigen is present in sufficient concentrations in the sample, it will bind to specific antibodies fixed to a paper strip enclosed in a plastic casing and generate a visually detectable signal, typically within 30 minutes.

PCR test: Stands for polymerase chain reaction test. This is a diagnostic test that determines if you are infected by analyzing a sample to see if it contains genetic material from the virus.

• Molecular Test: a diagnostic test that detects genetic material from the virus.

• Reverse Transcription Polymerase Chain Reaction (RT-PCR): one type of molecular diagnostic test.

Some of the at-home antigen tests have an overall sensitivity of roughly 85 percent, which means that they are catching roughly 85 percent of people who are infected with the virus and missing 15 percent.

Some of the at-home antigen tests have an overall sensitivity of roughly 85 percent, which means that they are catching roughly 85 percent of people who are infected with the virus and missing 15 percent.

Rapid tests are most accurate when used by people with COVID-19 symptoms in places with a lot of community spread. Under those conditions, a rapid test produces correct results 80 to 90 per cent of the time, she said.

Most of the at-home tests are antigen tests and are not as accurate compared to the PCR tests. Schmotzer said the antigen tests need more of a viral load to detect whether someone is positive. She noted an antigen test is most reliable when people are showing symptoms of COVID-19.

Despite the high specificity of antigen tests, false positive results will occur, especially when used in communities where the prevalence of infection is low – a circumstance that is true for all in vitro diagnostic tests.

Antigen tests are commonly used in the diagnosis of respiratory pathogens, including influenza viruses and respiratory syncytial virus. The U.S. Food and Drug Administration (FDA) has granted emergency use authorization (EUA) for antigen tests that can identify SARS-CoV-2.

The clinical performance of diagnostic tests largely depends on the circumstances in which they are used. Both antigen tests and NAATs perform best if the person is tested when their viral load is generally highest. Because antigen tests perform best in symptomatic people and within a certain number of days since symptom onset, antigen tests are used frequently on people who are symptomatic. Antigen tests also may be informative in diagnostic testing situations in which the person has a known exposure to a person with COVID-19.

In the United States, the tests can range from $7 to $12 each, making them too expensive for most people to use frequently.

Sometimes a person can test positive for SARS-CoV-2 antibodies when they do not actually have those specific antibodies. This is called a false positive.

Symptoms may appear 2-14 days after exposure to the virus. If you have fever, cough, or other symptoms, you might have COVID-19.

If you got tested on the fifth day after exposure or later and the result was negative, you can stop isolation after seven days. While in quarantine, watch for a fever, shortness of breath or other COVID-19 symptoms.

• 14 days have passed since their last exposure to a suspected or confirmed case (considering the last exposure date to case as Day 0); and
• the exposed person has not developed signs or symptoms of COVID-19

You can be around others after: 10 days since symptoms first appeared and. 24 hours with no fever without the use of fever-reducing medications and. Other symptoms of COVID-19 are improving*

*Loss of taste and smell may persist for weeks or months after recovery and need not delay the end of isolation​