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It also doesn't sound like it even lowers the bar for getting a diagnosis, even with all these caveats. You'd still need a CT scan, in a world where many can't even get a respirator.

I'd be more interested in a model that tries to give a preliminary diagnosis (positive or negative) based on data a patient already has with them or can get at home. An image of their throat, audio of their cough, maybe a time sequence of thermometer readings. If we could self-diagnose (or at least rule out some cases) using a smartphone, that would truly change the game.

I think everything that you've said is completely true. However, I'll add that it matters a lot more if you otherwise don't have testing capacity available, or if your test has a large false negative rate. China relied heavily on CT-based diagnosis to backstop a lack of available and reliable testing.

Another issue is that modern sanitation standards don't really enable using a CT to diagnose an infectious disease. The equipment is far too slow and expensive to truly sanitize, you would have to be willing to just PPE the patient and hope that works out. Again, perhaps better than skipping any diagnostic testing altogether if you don't have any alternative, but certainly not a first-line choice, and ethically questionable if you risk exposing uninfected people.

Actually you just need to have them wear a mask and wipe down the equipment with standard hospital grade wipes. We know now that COVID-19 is not airborne and is spread by droplets only so this would be routine precautions, unlike TB which we scan routinely and is an airborne pathogen.

The problem with CT is we know that the test is completely normal in 50% of patients from day 0-2, and 10-15% of patients up to day 5, and roughly 7-10% of patients up to day 10. These numbers are probably an under representation given how few people with the illness get CT imaging.

Additionally as has been stated the findings are considered only somewhat specific, we believe that specificity will decrease as more and more people will eventually get scanned and prove our findings thus far to be false.

That is why we (in radiology) currently recommend against the routine use of CT in screening or diagnosis of COVID-19 related illness as a negative test does not mean anything and a positive test is usually noncontributory (clinical diagnosis of COVID-19 infection already made). Additionally, this will rarely affect clinical management. The only potential argument being made is the small subset of people who have viral pneumonia and may theoretically avoid being asked to self-quarantine however I highly doubt in the present climate any infectious patient with a cough will be allowed/think it wise to roam the streets.

China has also removed CT from their sixth edition diagnostic manual for this disease as an aside.

Source is from STR/ACR, there is a good video below: https://veritastv.org/programs/covid-19

> We know now that COVID-19 is not airborne and is spread by droplets

What?! It was only, like, yesterday when I heard that "we know" pretty much the opposite. I'm less and less convinced "we know" anything at all.

There is a medRxiv paper from March 9 that suggests 3 hours half life in the air

Anyone who “knows” something is currently wrong, but there is evidence of possible airborne transmission

Can you provide this link?

I could only find:

https://www.medrxiv.org/content/10.1101/2020.03.09.20033217v...

Which does not actually address whether there is airborne transmission of the virus but rather refers to laboratory generated aerosolized particles and viability on various surfaces.

If you know otherwise please share as this is in direct contradiction to what various health organizations have been telling HCWs and forms the basis of our hospital’s standard of care which like all other in North America is that airborne precautions are NOT needed except during aerosolized particle generating procedures.

“Standard of care” is risk managed by a vast bureaucracy of counter-balanced interests. It is not designed to incorporate rapid learning of emerging unknowns.

During the exponential introduction of a new disease, the standard of care lags, badly.

Repeating “that goes against the basis” or “not needed” doesn’t make sense until the competing interests have settled on a new standard incorporating understanding of the new unknown.

Better to follow the emerging research, tailor care, document, and contribute findings back, to optimize the learning curve.

I don’t follow your logic. When COVID-2019 first became a thing the “standard of care” was to use airborne precautions and respirators, it did not “lag badly” as you so claim.

Two months of research later there has been no evidence that this virus can be transmitted by airborne particles (read: not droplets) and the standard of care was updated a couple of days ago to reflect that, hence why we now do not require negative pressure isolation rooms and respirators.

I don’t see where the lag is.

Previously, you wrote, "various health organizations have been telling HCWs and forms the basis of our hospital’s standard of care which like all other in North America is that airborne precautions are NOT needed".

Now you write, "'standard of care' was ... two months of research later ... the standard of care was updated a couple of days ago to reflect that".

Yet you comment, "I don’t see where the lag is."

The two months' lag was enough it's not at all obvious which standard of care you were referring to when you're saying no lag, the lagged standard or the just updated standard.

This very comment thread highlights the issue.

Here's yesterday's updated standard of care language in regional guidance. Recall that a standard of care also protects providers and facilities from liability. By relaxing it, both are less liable for things that may still be risks.

Looks like the language makes it clear the goal here is to preserve the supply of masks:

The safety of healthcare workers is a top priority for the Health Department. As we gain more understanding of COVID-19, our guidance will evolve. The use of standard, contact, and droplet precautions with eye protection is appropriate when caring for patients with possible or confirmed COVID-19. Personal protective equipment (PPE) should include: facemask (procedure or surgical mask) AND gown AND gloves AND eye protection (goggles or face shield).

The Health Department recommends healthcare workers do not need to use a fit tested N95 respirator or Powered Air Purifying Respirator (PAPR) for routine (non-aerosol generating) care of a COVID-19 patient. Patients can be evaluated in a private examination room with the door closed.

Supplies of PPE must be reserved for high risk procedures due to potential supply chain constraints.

Ample studies indicate the safety of droplet precautions which may also help prevent the complete exhaustion of fit tested N95 respirators and PAPRs; higher level PPE will continue to be needed to protect HCWs during critical and medically necessary aerosol generating procedures (e.g., intubation, suctioning) throughout the course of this outbreak.

Placing the patient in an AIIR and the use of a fit tested N95 respirator or PAPR is still recommended for aerosol-generating procedures (e.g., intubation, suctioning, nebulizer therapy) and when caring for patients with severe illness requiring intensive care.

Most nations have follow the WHO advice and have all dropped the requirement for airborne precautions/isolation rooms and we now use droplet precautions as we do with every other influenza and Coronaviruses. It is my understanding that the CDC has done so as well, partially due to supply chain issues but also largely given the lack of evidence of airborne transmission.

https://www.publichealthontario.ca/-/media/documents/ncov/up...

https://apps.who.int/iris/bitstream/handle/10665/331215/WHO-...

The article fails to ask the obvious next question: if this can potentially apply to much cheaper and instantaneous tests, maybe something ultrasound based? I'm not an expert on medical imagining, so can someone comment on ultrasounds' usefulness here?

Ultrasound has a ton of untapped utility and is a fantastic medical imaging modality. Like you said, the equipment is cheap and portable (can be pocket sized, even!). It’s near instantaneous, allowing you to image in real time. You can even measure blood flow velocity and see other physiology. (I could go on!)

But its great advantage over x-ray and CT, which is that it doesn’t use ionizing radiation, is also its greatest weakness. Ultrasound uses sound waves, of course, which unfortunately simply cannot travel very far in the body, and (critically) do not travel well across certain interfaces. One such interface is with air. Sound waves travel through your chest wall fine but on arriving at the lung... they just sort of fizzle out. Very little sound continues, and even less comes back to the transducer as meaningful signal.

So ultrasound is unfortunately very poor at seeing lung tissue. (It can show us some secondary findings of pulmonary disease in the lungs, such as fluid collecting in the thoracic cavity [a pleural effusion], but that’s yet another non-specific finding.)

Not entirely true.

Ultrasound actually has pretty good sensitivity for pneumonia (88%) and even higher if you look at the “difficult” cases requiring CT in the Cochrane review I link to below.

While the fundamentals of what you say are correct, consolidation by definition is the build up of fluid which is very well depicted by ultrasound. For a predominately peripheral airspace disease like COVID-19 ultrasound should theoretically be very sensitive.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279077/

I wasn’t aware lung US was at this point — I’ll have to read more!

> And they are time-consuming, costly, and harmful (they use radiation!)

To put things in perspective, I got a CT in China, and the imaging took less than 5 minutes, and cost $35 (just the machine, not reading). The radiation is less than the increased radiation than taking a flight to China.

While your perspective is probably accurate for the US, if you step back and think, it is no more complicated than getting grade school photos.

By my math, a chest CT is about 10x the dose from a flight. However, there is no “safe” level of ionizing radiation. There is only acceptable and unacceptable risk.

Right, one CT scan increases your lifetime risk of cancer 0.1%: https://www.scientificamerican.com/article/how-much-ct-scans...

Which isn't much for one person, but if you're CT scanning thousands of people, on average that's an extra case of cancer per thousand scanned.

The PCR test is probably more accurate and in the US, maybe even cheaper? Although it probably does have higher latency.

A lung CT can be done at about 1/5th the radiation dose of a chest CT. The future will decide if we took the correct risk with extremely limited testing in the early stages.

In my experience, “not my job” , “too much risk”, and “need more data to make a decision“ is the default attitude in the medical profession. People choose that career because it is safe, and very few doctors have military experience these days. That being said, people adjust to a new reality very quickly.

By the time pneumonia has occurred it’s too late for screening. This isn’t replacing rtPCR for people who are coughing.

Keeping everyone safe and antiseptic while you move a possibly COVID patient in and out of a CT scan will make the whole thing way more complicated and slow.