Timeframe for diving post covid +

[Lorenzoid]

Okay, @Nick_Radov, I'm obviously out of my league in this discussion, but what I meant was the kind of more severe infections that the experts here have mentioned. Influenza, mainly. I can't speak for others, but I haven't had a "cold" that affected my respiratory function in any way that I can remember, and I believe we have a long track record of successfully returning to diving after the common cold. I last had the flu about 20 years ago, but if I had it again today, and it knocked me out the way it did back then, I would consider being tested before returning to diving. I understand that most primary care physicians wouldn't have a clue about respiratory infections and returning to diving, and insurance wouldn't cover the testing, but maybe as individual divers we need to look out for ourselves and push for additional testing when the general public would not. Looking out for myself as a diver who decided to venture far from medical help on some dives, I have pushed for additional cardiac testing (at my own expense) when there was nothing to suggest to my primary care physician that it was "necessary."

 

[Nick_Radov]

I last had the flu about 20 years ago

Are you certain about that? About a third of influenza infections are asymptomatic (similar to SARS-CoV-2 in that regard). You could have been infected at some point without even knowing it.
If you want to get additional tests beyond the standard of care for your own peace of mind, then that's up to you and your doctor. But I am strongly opposed to over medicalizing every little thing for the general population. As a society we have limited healthcare resources and we can't afford to burn up doctors' time on screening the "worried well". Plus, every test has some rate of false positives, potentially leading to additional unnecessary medical procedures and the risk of iatrogenic harm.
SARS-CoV-2 is endemic and well never go away. The majority of divers have already been infected (even if they were never formally diagnosed) and most of us will probably be occasionally reinfected throughout our lives. If medical authorities and certification agencies try to impose some kind of strict screening protocol, then that will destroy the dive industry for everyone.

 

[duke dive medicine]

Perhaps - one of the things I’m trying to get a feel for is how common barotrauma was before Covid. I don’t practice dive medicine in specific, and my practice location does not see a lot of divers in general, so I don’t have a good feeling for the rate of injury pre-Covid. My gut is that on a per dive basis it is very low as likely thousands (tens of thousands?) of people dive worldwide every day.

The big rub about screening is the time and cost, as well as possible unintended outcomes of trying to make a healthy person “healthier”. Having the rate of injury would give some needed perspective.

It's very uncommon. Exact injury rates are difficult to ascertain because as you indirectly pointed out we don't have a solid idea of how many dives are made during any given time. In eleven years of hyperbaric nursing I never saw a diver with a gas embolism; in 20 years of Navy diving and seven years of commercial diving instruction I saw one confirmed AGE and one possible that was treated as one, both in training and with clear precipitating events. A friend of mine who manages a hospital chamber a few states away sees more AGEs just because he catches much of the business from an area with a high concentration of divers. He's never seen a gas embolism related to underlying lung pathology. That's probably not as detailed as you (or anyone) would like - DAN has accident statistics and their annual fatality report, but again there has to be a total number of dives to compare them to which unfortunately would come down to somebody's best guess - maybe not even expert opinion

Best regards,
DDM

 

[Seaweed Doc]

Are you certain about that? About a third of influenza infections are asymptomatic (similar to SARS-CoV-2 in that regard). You could have been infected at some point without even knowing it.
If you want to get additional tests beyond the standard of care for your own peace of mind, then that's up to you and your doctor. But I am strongly opposed to over medicalizing every little thing for the general population. As a society we have limited healthcare resources and we can't afford to burn up doctors' time on screening the "worried well". Plus, every test has some rate of false positives, potentially leading to additional unnecessary medical procedures and the risk of iatrogenic harm.
SARS-CoV-2 is endemic and well never go away. The majority of divers have already been infected (even if they were never formally diagnosed) and most of us will probably be occasionally reinfected throughout our lives. If medical authorities and certification agencies try to impose some kind of strict screening protocol, then that will destroy the dive industry for everyone.

Interesting discussion. Two quick thoughts:

1. I've been vaccinated for many things. I would say I've never caught those things. In reality, the odds are pretty good that I indeed was infected, and that my immune system took out the infection before I was symptomatic BECAUSE I was vaccinated. Isn't that pretty much how all vaccinations work? It's not that the bacterium or virus has to stay at least 6' (1.5 m) away from you because the vaccine police require it for vaccinated individuals. For that matter, opportunistic infections might fall in this category as well. Asymptomatic cases are a bit of a red herring in my view. (I'll leave it to more knowledgeable folks to decide if a positive COVID test is considered a sign/symptom or not. In my hypothetical asymptomatic infections, it's possible there wasn't enough virus or bacterium to test positive.)

2. I think DDM raised an excellent point that's getting missed. Covid is making us all realize we need to stratify patients with ANY respiratory illnesses. (And by "we" I mean all of you that treat humans.) That stratification may end up being based on symptoms, or it may be more cautious with some respiratory illnesses (e.g., COVID) vs. others (rhinoviruses) because evidence, experience, or logic indicate. UCSD has attempted this for COVID, which suggests they're on the right track.

3. In the United States, we're now aware that masking can reduce COVID spread (despite some cranks' claims). We really should do as some Asian cultures have done long before COVID and mask up when we have a cold. Or better yet, stay home and not try to tough it out at work if that's feasible.

 

[Dr Simon Mitchell]

Kinoons,

My main objection to your posting in this thread is your nihilistic portrayal ("failure of academic medicine" "guesswork" etc) of a diving medicine community trying to do the right thing in a difficult situation. This has been laced with an authoritative voice (you imply you are a physician but give no detail) and (sorry to say) naive demands for a randomised trial to resolve this issue.

When the pandemic broke, it did not take long for evidence of serious and sometimes persistent lung changes to emerge. It became clear that this could occur in patients who had suffered relatively mild illnesses. One of these changes was air trapping which, as I have pointed out previously, is an indisputable established risk factor for pulmonary barotrauma. Under these circumstances, it is no surprise that months into the pandemic the early guidelines regarding return to diving (including those published by UCSD) were conservative.

Those guidelines have subsequently been modified to reflect the fact that (as you have observed) many divers have undoubtedly returned to diving after covid with few obvious problems so far. You have condemned this as "guesswork" and demanded a randomised trial to resolve the issue.

It is easy to be a triallist sitting at a keyboard. I don't know how many randomised controlled studies you have published, but in case it is none, then I can assure you it is not straight forward. The big problem in this case is power. We don't know the exact incidence of arterial gas embolism secondary to pulmonary barotrauma in 'normal diving', but in our recent review article [1] we cited several studies with over 3000 cases of DCI in which the authors believed about 6% were AGE and the rest DCS. There is reasonable evidence that the incidence of DCI in typical recreational diving is something in the vicinity of 1:10,000 dives [2]. If only 6.5% of 1:10,000 are AGE then the problem is obvious. You would need a massive study (100s of thousands of subjects) randomised to a medical assessment or not to show any difference in the incidence of AGE between a medical assessment vs a no medical assessment approach. On this thread you were proposing that a research team would contact all these people in a lead up to a dive trip and ask half of them to submit to a medical exam that they were not intending having. The rate of subjects declining such an imposition would be huge, not to mention the extra-ordinarily difficult logistics of such an undertaking. I hope you can appreciate that an experienced triallist (which I am) would find the virtual impossibility of your proposal somewhat ironic in the context of someone criticising the field for "a failure of academic medicine".

Kinoons, many of your points are valid. It is becoming clear that the risk is lower than originally feared. The community is responding to that by modifying its guidelines to be less conservative. There are still anxieties about air trapping lesions (eg reference 2 in my previous post), but these will be appropriately calibrated over time. For the record, I agree with you that the CXR recommendation for cat 1 cases in the UCSD guideline can be questioned. If you go back to their original paper they address the logic for this, but I'm still not sure I agree with it for the reasons you state. I also agree that other serious viral illnesses can provoke lung changes, but they did not break under pandemic conditions equivalent to SARS-CoV-2. Moreover, they probably are mostly dealt with in much the same way was UCSD advocates when seen by diving physicians. A diver coming to me for any pulmonary condition that put them in hospital on oxygen or in intensive care would get a fairly thorough work-up before I would endorse return to diving.

Finally, I want to be clear to others reading this thread that I agree with the liberalisation of the guidelines for return to diving. I am not advocating for more screening. It will probably be even less over time. I am simply defending the path the medical community has taken through this difficult situation.

Simon M

1. Mitchell SJ et al. Decompression illness. N Eng J Med 2022;386:1254-64

2. Hubbard M et al. Decompression illness and other injuries in a recreational dive charter operation. Diving Hyperb Med 2018;48:218-23

 

[Nick_Radov]

1. I've been vaccinated for many things. I would say I've never caught those things. In reality, the odds are pretty good that I indeed was infected, and that my immune system took out the infection before I was symptomatic BECAUSE I was vaccinated. Isn't that pretty much how all vaccinations work?

Well, yes and no. Vaccinations don't all work the same way. I think what you're getting at is the difference between sterilizing immunity versus protective immunity. This is a spectrum — not a binary classification — and the immunity induced by any particular vaccine will fall somewhere in the middle. With true sterilizing immunity there is no growth of the pathogen in the patient's body, and they are unable to transmit it. The measles vaccine is pretty good at inducing sterilizing immunity in most patients but it's not 100%. By contrast, vaccines for respiratory viruses such as influenza and coronaviruses fall more towards the protective immunity side of the spectrum. They don't do much to prevent infection or transmission but are fairly effective at preventing severe symptoms in most patients. In general, it's just really hard to make a vaccine that would induce the type of mucosal immunity that would be necessary to sterilize such viruses.

Sterilizing immunity: Understanding COVID-19

Sterilizing immunity describes the elimination of a pathogen before it can replicate in the host. Here, Wahl and Wardemann describe the challenges of inducing and measuring sterilizing immunity. The authors discuss the relevance of sterilizing immunity for protection in the context of the...

www.cell.com

 

[L13]

You would need a massive study (100s of thousands of subjects) randomised to a medical assessment or not to show any difference in the incidence of AGE between a medical assessment vs a no medical assessment approach.

If a study of this size is required to detect any difference, doesn't that imply that the risk of not doing a medical assessment is very low? Possibly as low or lower than the risk for otherwise unnecessary assessments?

The larger the size of the trial needed to detect the difference, the more likely the adverse effects of the assessment are worse than the problem averted by the assessment. I have no idea where the curves cross.

 

[SlugLife]

I didn't read the entire thread, but it probably heavily depends on what symptoms you had. Some people are asymptomatic (meaning encountered the virus, but zero symptoms) and they should be fine to dive relatively immediately. Similar with people who had no respiratory symptoms.

I may have gotten covid the other day myself for the first time. Aside from being tired, I'd describe it as a mild flu, and no respiratory symptoms. I'm probably fine to go diving right now if I really wanted to.

 

[Dr Simon Mitchell]

If a study of this size is required to detect any difference, doesn't that imply that the risk of not doing a medical assessment is very low? Possibly as low or lower than the risk for otherwise unnecessary assessments?

The larger the size of the trial needed to detect the difference, the more likely the adverse effects of the assessment are worse than the problem averted by the assessment. I have no idea where the curves cross.

Yes, of course. Entirely correct. If the risk in COVID cases were dramatically higher than baseline then you would not need such a large study to demonstrate a difference from the (low) baseline risk. Under those circumstances a randomised or cluster randomised study might even be plausible. However, the emerging observational evidence suggests that the risk in those post-COVID patients who have returned to diving seems low, and per my previous post, it would almost certainly take an almost impossibly large study to detect a difference between divers who do or do not have medical evaluations.

To your main point, avoiding risk / harm / unnecessary inconvenience etc from over-investigation is exactly why the diving medicine community has dialled back its recommendations to a less conservative setting. We can expect related advice to continue to evolve.

Some people are asymptomatic (meaning encountered the virus, but zero symptoms) and they should be fine to dive relatively immediately. Similar with people who had no respiratory symptoms.

Yep, that's pretty much what the latest guidelines from UCSD and DMAC say.

Simon M

 

[Seaweed Doc]

Well, yes and no. Vaccinations don't all work the same way. I think what you're getting at is the difference between sterilizing immunity versus protective immunity. This is a spectrum — not a binary classification — and the immunity induced by any particular vaccine will fall somewhere in the middle. With true sterilizing immunity there is no growth of the pathogen in the patient's body, and they are unable to transmit it. The measles vaccine is pretty good at inducing sterilizing immunity in most patients but it's not 100%. By contrast, vaccines for respiratory viruses such as influenza and coronaviruses fall more towards the protective immunity side of the spectrum. They don't do much to prevent infection or transmission but are fairly effective at preventing severe symptoms in most patients. In general, it's just really hard to make a vaccine that would induce the type of mucosal immunity that would be necessary to sterilize such viruses.

Sterilizing immunity: Understanding COVID-19

Sterilizing immunity describes the elimination of a pathogen before it can replicate in the host. Here, Wahl and Wardemann describe the challenges of inducing and measuring sterilizing immunity. The authors discuss the relevance of sterilizing immunity for protection in the context of the...

www.cell.com

Thanks, Nick. This is very helpful. A question though:

With measles, I understand you don't get any symptoms at all (as opposed to just less severe symptoms) once vaccinated. However, I'm thinking that at least some human cells (epithelial, perhaps?) will get infected before killer T-cells or others take out the virus? Or do people who are vaccinated never even have this initial level of infection? I'm having trouble imagining the virus never invading a single cell before being wiped out by the immune response, unless it only infects immune cells that recognize it.

I'm taking this thread adrift a bit: Most folks probably don't care about it beyond "Will I feel sick" and "Will I die?" I also need to admit.

I'm a botany guy, long removed from micro classes where immuno was discussed, but I'm teaching evolution where HIV is used as an example so I've been thinking about immune system responses and viral infections.