Asymptomic carriers of COVID19 (i.e. Typhoid Mary)?
April 18, 2020 9:32 PM   Subscribe

I'm not asking about the stage of COVID19 in which people are initially asymptomatic. Rather, do we know yet if, and/or how long, people could be asymptomatic carriers of COVID19 (à la Typhoid Mary) – could it be indefinite (such as with Mary), or would it eventually progress to being symptomatic, or leave/burn out?
posted by WCityMike to Health & Fitness (13 answers total) 11 users marked this as a favorite
I think China and some other countries have been following individuals from when they test positive until they test negative twice. Some people are showing signs or reinfection in South Korea, so they are following people for awhile (on the scale of months as this virus is only 5 months old) But there hasn't been any news I'm aware of where people are testing postitive and then never testing negative.
posted by AlexiaSky at 11:00 PM on April 18, 2020

Here’s a fairly recent article on China‘s asymptomatic cases. They found a significant number don’t get any symptoms, but it seems they do “burn through” the disease and “recover” rather than remaining carriers.
posted by scorbet at 12:08 AM on April 19, 2020 [2 favorites]

The answer appears to be that we don't know, because there is not enough research and testing yet. E.g.

* What We Know About The Silent Spreaders Of COVID-19 (NPR, Apr. 13, 2020 "there are wide gaps in our understanding of [...] how much they contribute to transmission of the disease. [...] About 75% of people who test positive without showing symptoms turn out to be presymptomatic, displaying coughing, fatigue, fever and other signs of COVID-19 in a later follow-up exam")
* How Long Does It Take To Recover From COVID-19? (NPR, Apr. 13, 2020 "Aaron Carroll, a professor of medicine at Indiana University, says there's still some uncertainty. "We still don't have enough data to really know how long people are infectious," he says.")
* More evidence indicates healthy people can spread virus (AP, Apr. 1, 2020 "CDC officials say they have been researching asymptomatic and pre-symptomatic infections, but the studies are not complete.")
* How Long Can Asymptomatic Coronavirus Carriers Infect Others? (Huff Post, Apr. 1, 2020 "it is not known how long those carriers may be contagious.")
* Coronavirus Can Live in Patients for Five Weeks After Contagion (Bloomberg, Mar. 12, 2020 "Patients with the new coronavirus keep the pathogen in their respiratory tract for as long as 37 days, a new study found, suggesting they could remain infectious for many weeks.")
posted by katra at 12:20 AM on April 19, 2020 [7 favorites]

Lot of us may already have had it -- which is obviously good news. The article doesn't answer/ discus the super carriers angle, but focus on anti-bodies would indicate that these people are likely not carrying it anymore.
posted by zeikka at 7:35 AM on April 19, 2020

With the current crop of antibody tests, we are probably seeing a LOT of false positives. This means that many of the people who test positive actually have not been infected with coronavirus and would still be vulnerable to it.

Please see this clear explanation about why this is so: the problem is not unique to coronavirus, but has to do with test sensitivity and what happens if many people still haven't been exposed.
posted by Sheydem-tants at 3:57 PM on April 19, 2020 [1 favorite]

Anecdote: my spouse's co-worker came down with COVID-19 after the co-worker's child returned from college. The child's roommates also were infected. The child has still displayed no symptoms.

So yes, there are asymptomatic carriers.
posted by JawnBigboote at 4:52 PM on April 19, 2020

There is a real difference between what Mary Mallon had, and what asymptomatic carriers have, just to be clear.

Mary had an active colony of typhoid bacteria (not a virus) living in her gall-bladder, and she was also immune (or at least highly resistant) to the disease herself. But the bacteria remained, because her body had no immune response to it -- they didn't have the term at the time, but her "gut microbiome" was hospitable to the bacteria.

On top of all this, she did not wash her hands while serving as a cook. She had more than once been allowed to return to work on the condition that she maintain a better hygiene regimen and also work in a field that didn't involve food preparation, and failed on both counts, including taking kitchen work under false names. You don't get typhoid from someone exhaling droplets, you get them because someone doesn't wash their hands with soap after taking a shit. That is the only transmission.

Jump to today, and we have a variety of immune responses to COVID-19, but even the asymptomatic carriers are exhaling it, hence the masks. But on the other hand, the asymptomatic carriers are also fighting it -- they're having an immune response which will eventually overwhelm the virus. However, there is a chance for reinfection considering (a) we don't know how much immunity we get after surviving (could be years, could be less), and (b) immune-compromised people, even if they're surviving, may continue to shed virus because their bodies just can't fight it back all the way.

So the tl;dr answer to your question is: people who are asymptomatic with COVID-19 are only temporarily like Typhoid Mary, they will eventually purge the virus from their bodies. The longer-term danger of transmission comes from people who are immune-compromised, and those people (usually) know who they are and can take steps to avoid transmission.
posted by The Pluto Gangsta at 6:04 PM on April 19, 2020 [8 favorites]

Side note re: serology tests

A lot of people may have had it (even asymptomatically), and now have antibodies that would be detectable in a reliable test (which does not exist). Even so, presence of antibodies is not a reliable indicator of immunity. I think it was in Yong's Atlantic coverage, a doctor/scientist said (paraphrased): we've been studying whooping cough antibodies for twenty years, and we still don't know what level of antibodies confers immunity.
posted by j_curiouser at 6:07 PM on April 19, 2020 [3 favorites]

I think it was in Yong's Atlantic coverage, a doctor/scientist said (paraphrased): we've been studying whooping cough antibodies for twenty years, and we still don't know what level of antibodies confers immunity.

"“Even for diseases we’ve been studying for over 100 years, like whooping cough, we still don’t know what level of antibody would indicate that you’d be protected if you got reexposed,” said Sam Scarpino of Northeastern University, who studies infectious-disease dynamics. The only way to find out is through long studies." Our Pandemic Summer (Ed Yong, Atlantic, April 14, 2020)
posted by katra at 6:19 PM on April 19, 2020 [3 favorites]

Thank you! I knew I was gonna be wrong on some part of that. I got the gist, I think.
posted by j_curiouser at 7:21 PM on April 19, 2020 [2 favorites]

The AP published this today: Reports suggest many have had coronavirus with no symptoms, which includes studies of people who later developed symptoms, as well as statements about the need for additional testing and studies, e.g. "None of these numbers can be fully trusted because they’re based on flawed and inadequate testing, said Dr. Michael Mina of Harvard’s School of Public Health," and "Better answers may come from newer tests that check blood for antibodies, substances the immune system makes to fight the virus. But the accuracy of these, too, is still to be determined," and "scientists caution that there is still much to learn about whether mild illnesses confer immunity and how long it might last."
posted by katra at 10:41 AM on April 20, 2020

This online report suggests that there is no answer to your question yet: Furukawa NW, Brooks JT, Sobel J. Evidence supporting transmission of severe acute respiratory syndrome coronavirus 2 while presymptomatic or asymptomatic. Emerg Infect Dis. 2020 Jul ("knowledge of SARS-CoV-2 immunity among persons with asymptomatic or mild SARS-CoV-2 infection is needed; specifically, whether full or partial immunity develops in these persons, how long protective immunity lasts, and if it is possible to be immune from reinfection but still asymptomatically transmit SARS-CoV-2 while in a carrier state.")
posted by katra at 9:45 PM on May 11, 2020

This article makes a reference to Typhoid Mary: Could nearly half of those with Covid-19 have no idea they are infected? (Guardian, May 30, 2020) and reports "It took two months for Raje’s husband to recover. Repeated tests, done every five days, showed that Raje remained infected for the same length of time, all while remaining completely asymptomatic. In some ways it is unsurprising that the virus persisted in her body for so long, given that it appears her body did not even mount a detectable immune response against the infection."
posted by katra at 5:31 PM on May 30, 2020

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