Understanding COVID-19 testing

Testing for the virus

Sample collection: A swab is taken from the inside of the nose or back of the throat.

Processing: Molecular tests detect whether there is genetic material from the virus.

Positive test result

True positive: You are currently infected. Almost all positive results are true positives.

False positive: You are not infected, but test positive (very rare).

Negative test result

True negative: You are not currently infected. There is no risk of infecting others.

False negative: You are infected, but test negative. Can happen when the test is done too early to detect the disease or when sample collection is poor.

Positive test result: individual isolates.

False negative test result: unaware of their infection and could infect others.

Testing accuracy depends on when you get tested

Test accuracy based on a 5-day incubation period from exposure to symptoms.

Initial exposure

• Days 0-2: very low virus
• Worst days to test
• Approximately 98% not detected^{Footnote *}
• Those tested too early will be unaware of infection and may infect others

Incubating

• Days 0 to 5: virus multiplying
• Approximately 50% not detected^{Footnote *}
• Up to half of those tested will get a false negative result and may infect others

Symptoms

• Day 5 or more: virus plentiful
• Approximately 10% not detected^{Footnote *}
• Low false negative rate

Recovering

• Day 15 or more: virus decreasing
• May take longer to recover from severe disease
• May not be infectious to others

Testing for antibodies

A blood test detects antibodies to the virus that usually start to appear when a person is recovering.

This blood test is not used to diagnose active COVID-19.

Research is underway to find out whether antibodies protect you from future infections.