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Early tests at LAC-USC Medical Center show 5% positive for COVID-19 March 12-16; in Santa Clara on March 5, 4% had the virus. We need antibody tests.


Coronavirus by Engin Akyurt via (open access)

An article in the LA Times published March 31 related the results of tests performed March 12-16 on a series of patients with “mild” flu-like illnesses.  Of 131 patients screened, 7 came up positive on the RT-PCR test that indicates the presence of virus RNA in a person’s nasopharyngeal secretions.  This test is generally believed to show about 2/3 to 3/4 of actual patients, that is, a sensitivity of roughly 60-80%.  The sensitivity varies with the series and depends partly on the adequacy of sample collection, the type of swab used, and numerous other factors.  Theoretically, the test should show virtually all of the actual patients secreting virus through their noses and throats, but there are numerous barriers to such sensitivity.

The point is that, on performing screening of some of the many patients who were treated at that center, 5% were positive.  This would be described as a “point prevalence” (number of patients with illness at any one moment) in patients with symptoms– not necessarily with fever or shortness of breath.  Six of the 131 had fever and one had a cough.  All were described as “not so sick they would have stayed home.”  None of them tested positive for influenza or RSV (respiratory syncytial virus), common causes of flu-like illness.  Most importantly, none of them had travelled recently or had contact with a known case of the novel coronavirus.

In the article headlined in my last post, there is this nugget:

The California Department of Public Health and the CDC did not begin community surveillance for COVID-19 in Santa Clara County until March 5. Samples were collected from 226 coughing, feverish patients who visited four urgent care centers; 1 in 4 turned out to have the flu. The state tested samples from a subset of 79 non-flu patients. Nine of them had COVID-19.

These two screening studies performed a week or two apart in separate parts of California showed that the prevalence of COVID-19 in symptomatic patients was 5% and 4%.  This was nearly a month ago.  Imagine what the prevalence would be now.  We desperately need studies of blood antibodies to SARS-COV-2 in order to determine who is immune and can come out of lockdown and who must stay isolated.



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