References




  •  This article incorporates public domain material from the Centers for Disease Control and Prevention document: "Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19".

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Methods

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Positive viral tests indicate a current infection, while positive antibody tests indicate a prior infection. Other techniques include a CT scan, checking for elevated body temperature, checking for low blood oxygen level, and the deployment of detection dogs at airports. Detection of the virus Reverse transcription polymerase chain reaction Polymerase chain reaction (PCR) is a process that amplifies (replicates) a small, well-defined segment of DNA many hundreds of thousands of times, creating enough of it for analysis. Test samples are treated with certain chemicals that allow DNA to be extracted. Reverse transcription converts RNA into DNA. Reverse transcription polymerase chain reaction (RT-PCR) first uses reverse transcription to obtain DNA, followed by PCR to amplify that DNA, creating enough to be analyzed. RT-PCR can thereby detect SARS-CoV-2, which contains only RNA. The RT-PCR process generally requires a few hours. Real-time PCR (qPCR) provides advantages including automatio...
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Confirmatory testing

The WHO recommends countries that do not have testing capacity and national laboratories with limited experience on COVID‑19 send their first five positives and the first ten negative COVID‑19 samples to one of the 16 WHO reference laboratories for confirmatory testing. Out of the sixteen reference laboratories, seven are in Asia, five in Europe, two in Africa, one in North America and one in Australia.
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Infectivity

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Infectivity is indicated by the basic reproduction number ( R 0 , pronounced "R naught") of the disease. SARS-CoV-2 is estimated to have an R 0 of 2.2 to 2.5. This means that in a population where all individuals are susceptible to infection, each infected person is expected to infect 2.2 to 2.5 others in the absence of interventions. R 0 can vary according factors such as geography, population demographics and density. In New York state R 0 was estimated to be 3.4 to 3.8. On average, an infected person begins showing symptoms five days after infection (the "incubation period") and can infect others beginning two to three days before that. One study reported that 44% of viral transmissions occur within this period. According to the CDC, a significant number of infected people who never show symptoms are nevertheless contagious. In vitro studies have not found replication-competent virus after 9 days from infection. The statistically estimated likelihood of reco...
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