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Teenager transmits infection to 11 relatives after negative rapid COVID-19 test: MMWR.

2020-10-16
Muscat Avenue with green leaves

During this period (since February) I have been using this blog mostly to document new things I have learned about the novel coronavirus. There is a lot that I don’t document. There may be things that I do document that seem trivial. Nonetheless, each post reflects new knowledge that strikes me as important.

This article in The Washington Post (dated October 15) is an example of reporting about things that strike me as important (even if they are not entirely new): a case report, published in Morbidity and Mortality Weekly Report (MMWR) on October 5.

The Post article states that a 13 year old girl who tested negative twice spread the virus to 11 of her relatives during a three week period during which she visited families in four states. Her only symptom was a stuffy nose. Three of her infected relatives with symptoms tested positive only on blood antibodies, not on the nasopharyngeal (NP) swab with reverse-transcriptase polymerase chain reaction (RT-PCR)– which has been described as the gold standard but was early on shown to be false-negative in as many as a third of patients with confirmed infections.

The MMWR reports that eleven relatives who stayed in the same house with the index patient (the 13 year old) developed symptoms and were diagnosed as having COVID-19. Two other relatives who stayed in the same house did not develop symptoms, and six other relatives who stayed outdoors and distanced from the others also remained asymptomatic.

The index patient was exposed in a large outbreak in June and had a rapid antigen test four days after exposure (while she was asymptomatic) that was negative. The test she had was only approved for use during the first five days after symptoms develop, not in asymptomatic patients. This is an example of improper or inadequate testing, followed by failure to isolate.

She did develop a stuffy nose, but apparently was free of symptoms otherwise. This is an example of transmission from a relatively asymptomatic pediatric patient to numerous others, both children and adults. Eventually, she had a blood antibody test that was positive.

Three of the cases did not develop symptoms until two weeks or more after their first contact with the index patient. Two teenagers who were not counted as cases never developed symptoms (one tested negative by RT-PCR and the other was not tested.) Two teenaged cases developed symptoms late; one had a positive blood antibody test and the other was not tested. Both were counted as “probable” cases.

From the conclusion of the report:

This outbreak highlights several important issues. First,
children and adolescents can serve as the source for COVID-19
outbreaks within families, even when their symptoms are mild
(2). Better understanding of transmission by children and
adolescents in different settings is needed to refine public health
guidance. Second, this investigation provides evidence of the
benefit of physical distancing as a mitigation strategy to prevent
SARS-CoV-2 transmission. None of the six family members who
maintained outdoor physical distance without face masks during
two visits to the family gathering developed symptoms; the four
who were tested for SARS-CoV-2 had negative test results. Third,
rapid antigen tests generally have lower sensitivity (84.0%–97.6%)
compared with RT-PCR testing; negative results should be
confirmed with RT-PCR if used for persons with high pretest
probability of infection, such as those with a known exposure
(4). Fourth, regardless of negative test results, persons should self-quarantine for 14 days after a known exposure (5) or after travel
when mandated by state, territorial, tribal, or local authorities (6).
Finally, SARS-CoV-2 can spread efficiently during gatherings,
especially with prolonged, close contact. Physical distancing,
face mask use, and hand hygiene reduce transmission; gatherings
should be avoided when physical distancing and face mask use
are not possible (7).

https://www.cdc.gov/mmwr/volumes/69/wr/pdfs/mm6940e2-H.pdf

Thus, we see that rapid antigen tests are not as sensitive as RT-PCR and that a negative rapid test should be followed by RT-PCR when there is a high pre-test probability of infection. The CDC recommends that people in this situation should self-quarantine for 14 days regardless of the test results.

Equally important is the apparent absence of transmission of the virus to people who keep their distance and remain outdoors, even in the absence of face masking. This suggests that outdoor protest gatherings and even rallies are not likely to result in widespread virus transmission.

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