Not sure about the epidemiologist’s editorialization, and unclear how many those tested are truly asymptomatic vs presymptomatic … but another bit consistent with the hypothesis that the true infection rate may be much higher than the numbers used as the assumptions in the models, thus the true IFR may be much much lower and the number of resolved at various points of the curve much higher, than as modeled.
Stranger I asked if they’re feeling fine, not if their feline’s fine …
I wonder what studies will come from the USS Theodore Roosevelt which has over 500 positive cases so far. Soldiers tend to be young and healthy, so the symptomatic vs asymptomatic rate, death rate, etc. will be interesting to see from that.
But seriously, although I don’t think it is likely that domestic animals are a primary vector for spreading the disease, it is worth looking at whether they could harbor it (which felines apparently can) and whether they will produce enough to back-transfer to other humans, because that has implications for endemic spread. It would certainly not be the only case of such transfers.
I suspect, though, that a high degree of asymptomatic spread is primarily responsible for how rapidly this epidemic expanded and why there is so much untraceable community transmission. The antibody testing, once widely available, along with sample case histories should give us a more concrete answer.
The Roosevelt will be an interesting case study, but because of the close quarters and shared facilities it is a case of reinforced contagion that may not represent transmission trends in the population as a whole. However, because it is an almost fully contained population itself, it will tell us a lot about the absolute infectiousness of the disease.
And how many of those who test positive stay asymptomatic or with such minimal symptoms that they would not have noticed it if not under the microscope, and how many seriously ill to death. Also following up with serology testing (some of the negatives may actually be resolveds). A good complement to the Diamond Princess but with a younger healthier population.
Sorry for so much posting to this thread but another thought that limits high end estimates of asymptomatic rates -
Italy and Spain are now both over 300 deaths/million and NYC over 400 deaths/million.
Best estimates for symptomatic case fatality by the experts currently is 1%. If there are nine asymptomatic cases for every significantly symptomatic case then the Infection Fatality Rate would be 0.1%. Which would mean that 400 deaths per million would have required 400,000 cases/million, that is that NYC would already have 40% of the population infected two to three weeks ago (deaths lag). Now that is possible but start going to more than that asymptomatic rate and it becomes increasingly less and less believable.
Don’t be sorry, you and Stranger are both very informative about whats been going on, its been interesting to read.
Having said that, it was my understanding form the princess cruise that the final asymptomatic rate was 17.9%. At first it was nearly half, but most of them went on to develop symptoms.
FWIW, on the USS Theodore Roosevelt, where 550 sailors tested positive, the first sailor just died. Also 4 other sailors are in the hospital now. I’m sure its going to get worse but thats kind of disappointing. I assume most sailors are healthy people in their 20s, they aren’t frail elderly people.
Universal screening of 215 women coming in to deliver at a NYC hospital 3/22 to 4/4.
Total positive as currently infected 33/215 (15.6%). 4 symptomatic at the time (1.9%). 29 asymptomatic (13.7%) of whom 1 developed COVID-19 symptoms (two others unrelated postpartum fevers). One additional who tested negative but developed symptoms and was positive on repeat.
Adding it up 34 positive as being acutely currently infected (16%) and of that group 82% asymptomatic for the duration anyway.
Of those testing negative no way to know if they were resolveds or susceptibles. (Not counting the initially false negative.)
Theodore Roosevelt so far with 13% testing positive. Of them hospitalization rate 1.3%, ICU rate 0.3% including the death (0.015% infection mortality rate).
No report I can find regarding how many of the 98.7% who are infected but not hospitalized are ill and how many asymptomatic. Numbers may change. No report I can find if any serology testing has been done.
Asymptomatic rate (as of now, some could be presymptomatic, some could actually be resolveds) on the Theodore Roosevelt reported now as 60%.
I was expecting the asymptomatic rate to be higher myself.
Similar circumstance for a French aircraft carrier. Awaiting asymptomatic numbers but so far more in the hospital and no deaths.
Note that if this had to begin with an undocumented infection beginning likely March 10th-ish, a second wave beginning likely a week later so on for about maybe 4 to 5 cycles (?). R0 in these close quarters something like 3.5 to 4 then? Again antibody testing if done not reported.
Pooling the two ships we get a hospitalization rate of about 3% and an Infection Fatality Rate of 0.08%, subject to change with one from each ship in ICU and others potentially able to get sicker yet.
Numbers seem all over the place. But it seems very hard to get a tested cohort that isn’t in some way highly biased. Sailors on a naval vessel are very different crowd to pregnant women, are different to passengers and crew on a cruise ship, and so on.
Overall I have been assuming about 50%, for not much in the way of good reasons.
I do keep wondering whether the initial dose of virus is playing a part. Different modes of transmission making for different profiles of infection. A naval vessel is about as a bad as you could imagine for transmission. Maybe the confines tend to skew initial transmission to much higher quantities of virus, and more severe disease. Hospitals filled with the very sick making for a terrible place to receive an infection and maybe accounting for a noticeable higher portion of severe cases.
Little to support either, this but a personal hunch. (The thought would suggest Variolation may actually be a viable approach in the absence of a vaccine. Not that I imagine we would, or even could, go this route.)
Bear in mind that if the ~30% false negative rate of the CDC RT—PCR antigen test (which is what I assume they are using test sailors on the Roosevelt) then the number of infected could grow by a third (and the incidence of asymptomatic or presymptomatic cases would drop accordingly). It is probably too early to draw any conclusions about the ultimate infection fatality rate but given that the age demographics on a Naval vessel are going to be skewed with the median in the mid-20s (and virtually no one over 65) then it would be expected for fatalities to be much lower compared to the national population where the median is almost 40, with a spread all the way through retirement.
Stranger - actually the false negative rate would work the other way, increasing the asymptomatic rate, if we wanted to consider it. You can see such in a small scale with the women about to deliver data. Any who were asymptomatically infected and tested negative falsely were not included as infected. There was however one woman who was a false negative who then became symptomatic. She was retested, was positive, and counts as a symptomatic infection. False negatives who become symptomatic will likely be counted; false negatives who stay asymptomatic will be considered as negatives unless later picked up in an antibody study. Francis yes these are different samples of convenience and only hints at the whole.
Sailors are younger and more commonly physically fit, but also more commonly male (a risk factor). Overall not too different than the general population with 65% overweight or obese, 34% binge drinkers, 13.5% cigarette smokers, 37% with at least one chronic health condition (such hypertension or diabetes), so on. And of course stressed.
Women near term are a special group immunologically perhaps but also one would expect to be more likely to be compliant with social distancing than the general population.
But who knows?
They are small pieces that get put together complimentary to each other building a body of evidence that should be considered in aggregate. Even the antibody studies won’t be conclusive in and of themselves as some can have had infection and have minimal antibody response detected by the tests used. Are they still immune? Not? Unclear. Resistance to infection does not always correlate with specific titer levels. They clearly recovered and had mild infections. Maybe non-specific antibodies were a big factor and sufficient and still provoked some T-cell responses? In the actual preprint it is noted that younger patients were LESS likely to have high levels of specific neutralizing antibody. In any case the point remains that even antibody tests might not capture all the recovereds either.
Sorry, my lack of good copyediting made that unclear; the number of false negatives would increase the total number of infected persons including asymptomatic and presymptomatic, and given the timeframe I suspect there may be additional people who were exposed but not yet producing enough virions to test positive even for an accurate test. Even given the demographics I’ll be surprised if the eventual CFR of diagnosed cases doesn’t rise to 0.1%-0.2% which is inline of what is being seen for people in the 20s and 30s, though again antibody testing may reveal an even larger number of asymptomatic cases that drive that down.
Frankly, given the delay in evacuating crew from the ship, the tight quarters and shared facilities, and the apparent contagiousness of the virus, I’d be surprised if a majority of the crew were not infected. And if that is the case, it would be good news overall, in the sense that there is a significant portion of the population (at least of service age) who is essentially resistant to the disease despite the lifestyle factors you list, although not good news for the individuals who may be susceptible despite any obvious underlying factors or co-morbidities.
The initial viral load exposure very likely has some impact on the degree of infection and outcome, and in particular which part of the respiratory system the virus infects. Confined conditions, repeated exposure to large amounts of aerosol transmission, and the high stress conditions in an ER or ICU ward may significantly exacerbate the progression of the disease rendering normally resistant people to be more susceptible to ARDS or other aggressive presentations, which just reinforces the need to both physically distance as much as possible and provide effective PPE to both medical workers and other workers in essential industries that may be regularly exposed to contagion.
So in Santa Clara county, they found 50-85 times more infected based on antibodies than you’d expect based on confirmed cases.
But can this be extrapolated to other states? California only has about 24k confirmed cases out of a population of 40 million. New York has 220k conformed cases out of a population of 19 million.
If NY had 50x the infected rate vs confirmed cases, that would mean over half the state was already infected.
Don’t know about 50× but a massively larger than expected level of infections is my pet theory about how this is going. I am quite sure social distancing has a big effect but something else is limiting this disease.
This result is in the broad range I would have expected. Only a small fraction of those symptomatic get labelled as confirmed, and, as this thread has shown evidence for, there are some value of many more asymptomatic than symptomatic.
Currently they are running 69 deaths which likely reflects infection with onset in early April of a bit before. Using the 50K lower bound the Infection Fatality Rate would then be 0.14% which seems is in the range (albeit lower portion of it) I’ve been expecting these results would show.
I would not extrapolate from confirmed case count to other states as we know how those are a function of testing availability and protocols more than of cases and varies by locale and point in time. But to say that this makes one believe that the true population wide Infection Mortality Rate is closer to 0.2% than it is to 1% or higher as reasonable. That would mean that New York’s 626 deaths/million represents 31% of the state having been infected maybe three weeks ago, and closer to 52% of New York City, official count (and 70% if all probables count) if same death rate there … (but likely higher death rate there as a function of exceeding healthcare system capacity).
More believable if/when replicated elsewhere of course. But consistent with the blood donor study in Italy. Next weeks will either confirm or go against these numbers and then the models have some real inputs to plug in.
Not necessarily. It may just have been spreading longer.
The Imperial College model got the big share of the press but there was another one from Oford that ran a variety of hypotheticals. The study here and an explanation of it here. They used R0s in the 2.25 to 2.75 but varied the probability of severe infection in a range from 0.1 to 10%
The models work fine. The chosen inputs are the questionable part.
Of course Stranger has shared a model with a higher effective R as well.
These sorts of antibody studies can, if replicated, inform as to what the actual inputs should be.
If the IFR turns out to be not much higher than the flu, I wonder if there will be large scale social repercussions due to that. I think people will be pissed.
I don’t necessarily see why this would be the case since SARS-CoV-2 spreads more rapidly than the flu. If 1,000,000 people get infected and 0.1% of them die, that’s the same death toll as 100,000 people getting infected and 1% of them dying, for example.
