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THREAD on why I think the presymptomatic transmission period has made #covid19 especially difficult to stop.
-SARSCoV-1 viral loads peak ~5 days later & are higher in the lower respiratory tract compared to #SARSCoV2, which has a high level of shedding from the upper resp tract
-compared to influenza, in which people who are asymptomatic generally have lower viral loads in the upper respiratory tract & shorter duration of shedding than those w/ symptoms, the same does not seem to hold for #SARSCoV2

nejm.org/doi/full/10.10…

nature.com/articles/s4159…
Most of this is not new- we had suspicion (multiple articles in both @NEJM & @JAMA_current in *February* suggesting that we had asymptomatic & presymptomatic transmission), yet for some reason-likely lack of tests- our strategy has for quite a while focused on symptomatic cases
This was posted online on January 30th. #covid19

nejm.org/doi/full/10.10…
More here⬇️ I had tweeted a thread on many of these articles way back in early March.

#covid19
jamanetwork.com/journals/jama/…
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Abraar Karan, MD MPH DTM&H
@AbraarKaran
1/ Presymptomatic transmission is one of the most complex parts of controlling the #covid19 epidemic.

Quantitative #covid19 viral loads have been found to be equally high in those with or without symptoms.

nejm.org/doi/full/10.10…
2/ This @NatureMedicine paper estimated presymptomatic #SARSCoV2 transmission as being responsible for nearly half (44%) of secondary cases.

nature.com/articles/s4159…
3/ A strategy that only focuses on those with symptoms is likely to fall drastically far behind in terms of curtailing transmission.

We need far more testing, likely sequentially a few times over the possible incubation period of 14 days in suspect cases

annals.org/aim/fullarticl…
Read 7 tweets
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Abraar Karan, MD MPH DTM&H
@AbraarKaran
THREAD on my new op-ed in WaPo

1/ I spent the last 2 weeks on clinical service in our emergency room #covid19 pod.

Caring for patients was tough, but it was even tougher knowing that sending them back home would likely mean infecting their families.

washingtonpost.com/outlook/2020/0…
2/ So many patients shared the exact same story- index case was a healthcare worker or other front line worker who got sick on the job. They tried to take care of themselves at home; got more ill; family tried to both avoid them/help them; family got sick as well.
3/ This was particularly devastating when it ended up that a son or daughter accidentally infected their parents, some of whom were old and had comorbidities, became critically ill, needing admission +/- a ventilator; some even dying within a couple of days. This was really hard.
Read 12 tweets
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Abraar Karan, MD MPH DTM&H
@AbraarKaran
New study @NatureMedicine estimates that nearly half of #covid19 transmission occurs in the 2-3 days before any symptoms, & peak infectiousness may be close to the actual day that symptoms start.

nature.com/articles/s4159…
“Significant presymptomatic transmission would probably reduce the effectiveness of control measures that are initiated by symptom onset, such as isolation, contact tracing and enhanced hygiene or use of face masks for symptomatic persons.”
This is why rapid diagnostics & wide community testing of people who are symptomatic AND those who are pre-symptomatic or asymptomatic w/ exposure to known cases- is critical. If we have to wait for symptoms to start, we may get too far behind. #covid19
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