Effect Measure

When swine flu poked its head above water in the northern hemisphere in April our “normal” flu season was just ending. A surge of swine flu cases during a time when influenza was not usually seen was bewildering and confusing, not to mention alarming. We didn’t know what to expect nor were we sure if it would peter out over the summer, as flu usually seems to (we may learn differently in the future as we start to do surveillance over that period) and then come roaring back or just disappear. While it didn’t peter out very much, the big question was going to happen when the northern hemisphere entered its traditional flu season when, for reasons we still don’t understand, influenza infections greatly increase. CDC’s official flu season has been week 40 of one calendar year (October) to week 20 of the next (April). But this was a pandemic strain so we didn’t know how it would act when it had to compete with seasonal flu viruses under environmental conditions that seem to favor infection. So almost immediately eyes turned to the southern hemisphere which was on the cusp of its usual flu season (6 months out of phase with ours). We still don’t have all the results but a paper published this week in the New England Journal of Medicine summarizes experience with critical care bed demand in Australia and New Zealand.

The demand for critical care beds (“Intensive Care Units”) is one of the nasty problms in an increasingly brittle health care delivery system in the US. As noted in an earlier post, it is quite common for big city hospitals to have periods where they are “on diversion,” meaning that ambulances carrying patients to their emergency departments (ED) are diverted to another hospital, not because of lack of space in the ED but because of lack of staffed critical care beds. I am told much of this may be the result of stupid scheduling for elective surgeries (not spreading them evenly throughout the week), but in general ICU beds, especially those with mechanical ventilation, are the neck of the acute care hourglass. So it’s useful to make some back-of-the envelope calculations to see what might happen:

We performed a multicenter inception-cohort study involving 187 ICUs in Australia and New Zealand ? all the ICUs (adult, pediatric, or adult and pediatric) in the two countries.12 The ICUs had a total of 1879 beds, of which 1449 were equipped for mechanical ventilation.. . .

From June 1 through August 31, 2009, we identified all patients admitted to the ICU with confirmed infection with the 2009 pandemic influenza A (H1N1) virus. The 2009 H1N1 influenza was confirmed by means of a polymerase-chain-reaction (PCR) assay or serologic analysis. The 2009 pandemic influenza A (H1N1) virus and seasonal subtypes (preexisting H1N1 and H3N2 strains) were confirmed by PCR assay. (ANZIC Influenza Investigators, NEJM)

The investigative team obtained data for each patient on dates and times of admission and first symptoms, medical condition on admission (especially airway status), age, sex, race, BMI [Body Mass Index], pregnancy or childbirth less than 28 days previously and a large number of pre-existing medical conditions. 856 patients with laboratory confirmed influenza A infection wound up in an Australian or New Zealand ICU in the 3 month period, 722 (84.3%; 626 Australia, 96 New Zealand) with identified swine flu. Most of the rest were not able to be typed further and it is likely many or perhaps most were also swine flu cases. 37 patients (4.3%) had infections with identified seasonal flu subtypes (seasonal H1N1 or H3N2), so of the influenza patients in critical care beds, the overwhelming proportion were swine flu cases. Comparing this number (722) to previous years for patients admitted to the two countries’ ICUs for the general category of viral pneumonitis (which includes seasonal influenza A) the numbers are 57 in 20º5, 33 in 20º6, 69 in 2007 and 69 in 2008 (mean of 57 patients for the same 3 month period that yielded 722 this year; the seasonal flu number of 37 is on a par with other years). So the admission rate for influenza is at least 15 times higher than in other years. It still represents a minority of ICU admissions, however.

The ICU admission rate for Australia and New Zealand (combined population of roughly 25 million) was calculated as about 30 per million (I have rounded slightly because these are estimates). In the US, with a population of 300 million, this would amount to about 9000 ICU bed admissions for swine flu over a comparable 3 month period (the flu season isn’t over in the southern hemisphere but the objective was to get some preliminary data that would be of use to planners in the north).

How does this compare with the US? According to Table 3 in this paper (subscription only, I’m afraid) in 1999 the US had 5.7 million adult ICU admissions/yr. (so this underestimates a bit because pediatric ICUs aren’t included but it’s likely we have fewer beds per population than before as well; it’s the best data I could find). So that’s roughly 1.3 ICU million admissions in a three month period. If swine flu contributes another 9000, that’s not much added burden (maybe 1%) and even in terms of bed days it’s only about 2% of the total bed days, although it will be very unevenly distributed, with some places hit hard and others barely touched. As usual with flu, the paper showed a lot of geographic variation. It also showed usage peaking 4 to 6 weeks after the first winter admissions for swine flu, so we have yet to feel the bite in critical care beds. It’s also important to remember that beds don’t care for patients, nurses and doctors do, and staffing shortages is another area where we have been having trouble. I expect that we’ll be seeing some trouble spots, but the data as we see them here don’t suggest a looming catastrophe. We’ll find out soon enough.

The striking epidemiology of swine flu seen elsewhere is again confirmed in these data. The two graphs below show rates and numbers for different age groups. The top panel gives rates, and the highest risks are seen in the 0 to 1 age broup (babies), followed by adults in the 25 to 64 year old age ranges. But because there are so many more people in the 25 to 49 year olds, the numbers of ICU admissions in that age group is highest (bottom panel). Consistent with the initial stages, risks in the over 65 group are relatively low (as are number of ICU admissions), unlike seasonal influenza where they represent most of the severely ill flu cases.

i-e4ed68fb3ad6194cb6107b9ee99f52fc-NEJMoa0908481f2.gif

Major risk factors are a BMI over 35 (CDC considers 30 to be obese; a five foot six inch female with a BMI of 35 would weigh 216 pounds and a 5 foot 10 inch man 243 pounds; table here). Almost a third of the ICU admissions had a BMI over 35, a level of obesity found in only 5% of the population down there. During the same period it was estimated that about 1% of the population in those two countries was pregnant, but pregnant women made up over 9% of the ICU admissions, once again confirming pregnancy as a major risk factor. Among other pre-existing medical conditions, asthma and chronic pulmonary conditions were present in about a third of the ICU admissions but estimated to be only 13% prevalence in the general population. Being a member of one of the indigenous populations was also a risk factor, something seen in Canada’s First Nation and eskimo communities as well. But about a third of the ICU admissions were in healthy adults with no known predisposing factors.

As might be expected with people admitted to ICUs, these folks were pretty sick. About half had Acute Respiratory Distress Syndrome (ARDS) or viral pneumonia and 20% had a secondary bacterial pneumonia. Once again, if the thought is that modern medicine will save us because we have antibiotics and respirators, these data don’t suggest this will make a major impact. Interestingly, the proportion who died (about 16%) is essentially the same as people who were admitted to the ICU for regular seasonal flu subtypes. The main difference is in the ages: with swine flu it’s people below the age of 65, with seasonal flu it’s people over the age of 65.

We don’t know how much relevance these data will have for countries in the northern hemisphere, where the availability of critical care beds varies dramatically among developed countries as do medical care practices. Complicating this is the recommendation if not requirement that patients with swine flu be isolated, meaning that the usual multibedded ICU may be unsuitable, putting added stress on resources. Since total increase in demand is only a few percent, if it is not too sharp and too high it should be possible to make adjustments by converting acute care beds to critical care beds and postponing elective surgery. Hospitals that have done some pandemic planning will be much better off than those that haven’t. Unfortunately many have only paid lip service to detailed planning. They hospitals will struggle if hit suddenly.

The big unknown is what effect the timing, availability and uptake of swine flu vaccine will have. There was no vaccine for swine flu throughout the time reported by this paper. No one has any good idea what will happen in the northern countries now that flu season is starting. I’m taking out a public health insurance policy and getting swine flu vaccine (I already got the seasonal flu shot) as soon as my turn comes up, even though I am in the lower risk age group. The risk is still substantial and it’s the most rational thing to do.

I try to be rational about things, although I’m not always successful. This one I’ll make sure I succeed at.

Comments

  1. #1 Curious
    October 10, 2009

    Is it possible to be reassured and frightened at the same time? Because while these numbers make it hopeful we aren’t heading toward catastrophe (though they still are scary — 15-fold increase!), the news about the rapid rise in pediatric deaths kept me up last night.

    Do you think the rise is due to the massive increase in cases? Or is something more sinister going on? This is when I think counting cases would be helpful to put things in perspective, though I realize that’s not possible.

  2. #2 revere
    October 10, 2009

    Curious: Two things. A 15x increase is a big increase but it’s 15 times a small number to begin with. That makes the increase a possibly unstable estimate. But it also reflects the fact that the epidemiology of this virus is different (it is a pandemic strain). That means its CFR may be the same as seasonal flu but it is (rarely) killing a different age group, one that is much more anxiety producing. That difference in epidemiology is what makes this virus different and something to reckon with. I’ll probably do a peds mortality post tomorrow if I have the time to get one together.

  3. #3 Julian Lieb,M.D
    October 10, 2009

    In 1981, I published the first of nine review articles on the remarkable immunostimulating and antimicrobial properties of lithium and antidepressants. Immunostimulation, propagandized as unavailable, has in fact been available for more than a quarter of a century, but suppressed by vested interests. A few doses of lithium, or perhaps an antidepressant in some cases, could sufficently stimulate immune function, and inhibit viral replication, to rescue some of the ailing.

  4. #4 stefano
    October 10, 2009

    If I am not wrong, australian and New Zealand data report that only 5-10% of people were estimated to be H1N1 positive.
    This is consistent with our knoledge that seasonal flu are generally milder than in northern emisphere ( probably for climate and population density)

  5. #5 Ron Law
    October 10, 2009

    The 15 x figure is wrong and should have been picked up during the peer review and editing processes. 15 x 57 = 855… more than the entire study group.

    There were 48% ARDS AND viral pneumonitis… yet the 57 figure only related to viral pneumonitis… so the paper was comparing apples with oranges.

    The fact is that intensive care units were not swamped… they coped with the workload which may have been different to previous flu years, but in fact did not result in any ‘code purples.’

    The main fact as pointed out in your article is that the system was able to cope well with the flu season. There was no unusual absenteeism… society kept going as normal… schools only closed when forced to do so for political reasons at the beginning of the season… transports systems kept going as normal, etc, etc.

    Regards

    Ron Law
    New Zealand

  6. #6 Ron Law
    October 10, 2009

    Stefano, In New Zealand over 11 percent of the 4.3 million citizens were infected this past winter with 18 deaths. That’s an infection fatality rate of 1:26,000. Similar figures exist for australia and even new york city. Applying that to the 4,000+ deaths reported globally that equates to 105 million infections. Assuming 700 deaths in the USA that’s 18 million infected in the USA so far. The CDC was reported last week as saying that 5-10 percent had been infected in the US… that’s 15-30 million already infected!!

  7. #7 revere
    October 10, 2009

    Ron: I don’t have the paper in front of me and I’m trying to cope with two screaming grandsons aged 28 months and 14 months, but I think the 15x figure is for the entire flu associated ICU admission, not just the swine flu. Since past years didn’t have swine flu, the comparison was the correct one. They also didn’t have data on flu admissions so the used viral pneumonitis as a surrogate. This is all spelled out in the paper and the main points are unaffected by this.

  8. #8 Paula
    October 10, 2009

    This is interesting and, to a degree, reassuring data. (Wish there were some way to have actual data on numbers infected!) Sadly, though, none of this may help much in rural areas, such as mine, where hospital (and related) preparation is minimal and slow, and where trained ventilator nurses are rare, ICU beds scarce, equipment not state of the art, etc. And only cold water faucets in the primary-grade schools.

  9. #9 Paula
    October 10, 2009

    Oh yes–and where the entire county received a bit 200 doses of vaccine last week, and where the sole hospital, after finally scheduling a seasonal flu clinic the week before, only two days later discovered it was out of (seasonal flu) vaccine and could not get more.

  10. #10 Jason Dick
    October 11, 2009

    Very interesting that people over the age of 65 seem to do better against this new swine flu than they do against the traditional seasonal flu. I wonder if this means that this pandemic strain will die out rather quickly once people have immunity, or whether it just has some evolving to do to catch up to the previous seasonal flu.

  11. #11 Barb
    October 11, 2009

    I visit this site once in a while to catch up on the latest on H1N1. I have 4 high schoolers who think I am just way too cautious, a ‘germaphobe’, to be precise. I shrug it off and still make them take their vitamins if they want the car, especially D, as I have read up on its antimicrobial effects. I know more research is needed on D, but I am surprised this is not mentioned more in the mainstream media. Seems like the best kept secret. Sometimes anecdotal evidence is more powerful for me than no articles at all. Are the drug companies afraid of vitamin research? I’ve not had a common cold in quite a few years…

  12. #12 revere
    October 11, 2009

    Barb: Vit. D has come up fairly often in the comments but rarely in the posts. The science behind vit. D is interesting and evolving but its relation to flu, although possibly important, is mainly speculative, although some of the speculation is plausible. My personal opinion is that it has not reached the point where I could possibly advise vit D supplementation as a way to prevent or treat flu. Moreover vit. D is fat soluble, so it can be toxic and people have a tendency to think, “if one vit. T capsule is good, ten are ten times as good.” My nutrition advice is the same as the one my old school GP father always gave his patients, “Everything in moderation.” Eat a balanced diet, including sources of vit. D. and go out in the sunlight and don’t sit (as I am doing) in the dark in front of a computer screen all the time. Vit. supplements are mainly for the lazy or diet careless, IMHO. But that’s just me.

    Anyway, that’s the explanation for not talking more about vit. D in the posts.

  13. #13 Barb
    October 11, 2009

    I appreciate your advice. Again, I am working with teenagers whose diets can be defined by carelessness and laziness if not taste and convenience. As far as my part, I try to cook healthily for them but a single mom, employed full time,on the run, only has so much time…I take D myself as a physical therapist in a long term care facilty. I wish the residents would be at least tested for levels. Maybe they would not be as ill, but then the facility would have to pay for those tests and supplements, huh? First do no harm, I know…so I am testing my family soon. Ignorance can be just as harmful if not blissful…enjoy your blog!

  14. #14 Don S
    October 11, 2009

    Thank you for this analysis, as far as it went (no offense intended): the adult ICUs in America are at low risk of exceeding surge capacity. Allow me to attempt to extend this to what may turn out to be the most critical bottlenck however: Peds ICU surge capacity.

    I refer the interested reader to an article calculating surge capacity in the New York City metropolitian area http://pediatrics.aappublications.org/cgi/content/full/119/1/94

    At the time of that analysis that region the conclusions included the following:

    “If an attempt was made to provide usual standards of intensive care, vacancies would not reliably accommodate as few as 25 children (total number) in trauma center PICUs (Fig 3: curve a), or in all regional PICUs, with or without trauma center designation (Fig 4: curve a). Increasing capacity through a discretionary modification of discharges and admissions and a reduction in care standards sufficient to quadruple the number of new patients admitted to each PICU vacancy would substantially improve the situation. As a result, intensive care could be reliably provided for 63 children per million (a total of 100 new children) (Fig 4: curve d).” {That’s, I believe, per million age specific population}

    Also “Reducing standards of care would reliably permit hospital care of 500 per million children in the New York City region in a disaster. Depending on the proportion of critically ill or injured patients, PICU beds may be insufficient even with modified standards of care.”

    So how do these numbers fit into those simulations?

    Infants ran about 75 ICU admits/million age specific population, and for older children significantly less. But that is spread over a season, not all at one time – so if we run similar numbers, and we are willing to implement the measures discussed in the reference article, and most of the country has the PICU capacity that the NY area has, then we should be able to skate by, albeit perhaps getting close. OTOH, if our higher population density makes for a higher attack rate (and their overall attack rate seems low, about the same as most typical influenza years, about 11% overall – see http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19319), or other regions do not have the NY area’s surge capacity, or the cases all clump together in one big peak, then not.

    As for pediatric hospitalizations overall – if we have the 30-40% overall attack rate that many experts predict and the 0.5% overall hospitalization rate per child infected that seems reasonable, then we’d have about 1500 children per age specific million of population over the season, which only stays within that 500/million if it is evenly spread out over three months – something not too likely.

    Of course if we have that attack rate then our PICU admissions go up to. The Down Under experience is consistent with others in that 20% of all admits end up in the ICU – that would get us to about 300 PICU admits/age specific million population – and for that number even spreading out evenly over 3 months is not enough to get below a number that overwhelms PICU surge capacity.

  15. #15 revere
    October 11, 2009

    Don: I couldn’t find data on PICUs and you might well be right that it will be the choke point. The adult ICUs have more flexibility as the elective surgeries can be put off or rescheduled but the PICUs don’t. There is also the issue of vents for that population. If you find data on PICUs post it here.

  16. #16 Ron Law
    October 11, 2009

    Revere, the NZ total infected numbers are here… about 11 percent at a similar point in time to the ICU paper.

    http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19319

    The NZ, Australian, New York data and even CDC comments point to an infection fatality rate (IFR) of about 1:25,000 meaning that about 100 million people have already been infected.

    The peak ICU occupancy in Australia and NZ was 7.5 beds per million… for the USA that would equate to about 2,200 beds. The USA has about 100,000 ICU beds and about 60,000 ventilators… http://www.cdc.gov/nchs/data/ad/ad391.pdf

    the CDC has about 5,000 extra ventilators in reserve as doing many states… NY is reported to have about 5,000 on standby too… (of course that doesn’t mean there are extra staff but in emergencies people cope with things if they need to.)

    The fact is that in Australia and NZ the system coped… as always happens in winter flu causes problems with a combination of extra patients and fewer staff. There were no reports of extra staff vaccancies due to H1N1v flu.

  17. #17 Ron Law
    October 11, 2009

    Don and Revere, the New York PICU papaer is talking about a single sudden influx of patients due to a disaster rather than influenza which would cause a surge over several weeks. The only mention of influenza in the paper is this; “Some anticipated disasters would exceed targets of 500 per million. For example, a severe influenza pandemic might cause illness in 300 000 per million, with hospital care required for 33 000 per million, and mechanical ventilation for 2400 per million, over the course of the pandemic.25 Limited stockpiles of mechanical ventilators are likely to be a critical factor, which is not accounted for in the present study, in accommodating critically ill or injured patients.10″

    Note that the experience with this flu (indeed any flu) is that about 1/3rd have asymptomatic infection, about 1/3rd have cold like symptoms and about 1/3rd have what is commonly called ‘influenza.’ Australia and New Zealand had infection rates around 11 percent (110,000 per million) with admissions around 240 per million [not 33,000] and ICU admissions of around 30 per million and those requiring mechanical ventilation of 20 per million [not 2,400].

    The paper says, “Hypothetical scenarios were assumed to involve a single mass casualty incident with patient numbers as large as 500 per million age-specific population.1 This corresponds with 800 hospitalized children, 0 to 14 years of age, in the New York City region. The regional population in this age range is 1.6 million.15 For analysis of PICU resources, it was assumed that critically ill or injured patients accounted for up to 30% of the hypothetical total, consistent with historical reports of pediatric and adult mass casualty events.16–18 This would correspond with as many as 150 children per million, or a total of 240 hypothetical PICU patients for the region.”

    The Australia NZ experience provide huge reassurance that the system will cope with any expected surge. Indeed, NYC has already been through a phase where about 10% of the populace have been infected already… and coped.

    The maximum number of beds occupied at any time was 7.5 per million. Note that whilst numbers were high for <1 year olds they were very low for the other age groups up to 14 yrs old. Larger teenage children could easily be transferred to adult ICUs if required giving a degree of flexibility.

  18. #18 Don S
    October 12, 2009

    Ron,

    I am aware that the New York City study was modeling an acute disaster scenario; it does however model the limits of pediatric surge capacity. Integrating that study of the NYC region’s pediatric surge capacity and the Australian/New Zealand overall ICU experience with swine flu to the question of American surge capacity this Winter has many limitations:

    - Why was New Zealand’s (and presumably Australia’s) overall rate of infection so low? Is an 11% overall rate of infection something that we should be expecting here? Or are the predictions of a 30 – 40% rate still more likely? That answer is partly contingent on vaccination rates and timing and a variety of differences in our societies.

    - How concentrated will the peak period of influenza morbidity be as opposed to spread out over many weeks to months? How “sticky” will the patients be?

    -Is the NYC region reflective of surge capacity across the country? In general pediatric ICU capacity is significantly concentrated in urban centers and I suspect that the NYC region is better positioned than many other urban centers let alone the country overall – I do not know that however.

    This study is not a “huge reassurance”; it has some reassuring aspects and some aspects that give cause for significant concerns. No more and no less.

    We know that Australia/New Zealand had about 15x more ICU admissions overall and that they were particularly greater in younger cohorts. We know that a representative major urban center can handle a surge peak of 63 PICU admissions per million age specific population. The open question is still what the likely peak surge in America will be and how most of America can handle it.

    Typically (see http://pediatrics.aappublications.org/cgi/content/full/118/6/2409 ) admissions for influenza range “from 6.3 to 252.7 per 100000 children. The highest rates were in children younger than 6 months, and rates decreased with increasing age. Forty-nine (15%) children had an ICU stay; 27 required mechanical ventilation, and half of these patients were >2 years of age.” If we pick the middle of that range, and we multiply the end result by just 15 (and PICU admissions were likely more than 15X if overall was up 15 and it was shifted to younger age groups), we end up with 2250 per million age specific population needing PICU over the course of the epidemic. If we assume that half of that total occurs over a 4 week peak period and that each admission stays in the PICU for 7d, then we’d peak at over 280 PICU patients competing for a maximum of 63 PICU beds persisting for that 4 weeks

    (Please double check these calculations – if I have erred I would love to be corrected.)

    Now that’s a lot of assumptions and a lot of unknowns and the fact that we have not heard of infants on Australia who suffered from lack of PICU spaces reassures but I do not see how to read this as hugely reassuring.

  19. #19 Don S
    October 12, 2009

    I obsess only because I can find no one else calculating these figures out. I realize that others are better equipped than I, but the question needs answering, so I do the best I can …

    Another stab at baseline numbers, this study more broadly US representative than the Salt Lake City one above – http://content.nejm.org/cgi/content/full/355/1/31

    “From 2000 to 2004, an average of 0.9 per 1000 children 0 to 59 months of age were hospitalized with laboratory-confirmed influenza (95 percent confidence interval, 0.8 to 1.1 per 1000) with annual variations according to age group, year, and site (Table 3 and Figure 1). Average annual rates of hospitalization attributable to influenza were 4.5 per 1000 children 0 to 5 months of age (95 percent confidence interval, 3.4 to 5.5 per 1000), 0.9 per 1000 children 6 to 23 months of age (95 percent confidence interval, 0.7 to 1.2 per 1000), and 0.3 per 1000 children 24 to 59 months of age (95 percent confidence interval, 0.2 to 0.5 per 1000). …

    … 4±2 percent were admitted to the intensive care unit”

    @1 per 1000 (1000/per million age specific) hospitalization rate * 4% ICU regular baseline = 40 children in PICUs/million age specific during the course of a normal influenza season. Multiply 15x usual ICU rate equals 600/million age specific PICU admits for the swine flu season to come. Again accept the same half of the season occurring in a 4 week peak period and an average stay of 7d (as per the Southern hemisphere experience) and that’s an average PICU census of 150/million age specific population. Of course this is for those under 6 yo only.

    Well that’s better than the 280 but also well above the 63 PICU surge capacity calculated for the major metropolitian area of NYC. Given the roughness of choosing 100 as a middle range between 6 and 253 in the first stab, I am amazed it is that close really.

    PLEASE explain to me why I am wrong here. Believe me, I know that I can miss some things and I’d love to find out that such is the case. I really want to be wrong here.

    Until then I am concerned at what I have not heard – I have not heard tremendous planning about what to do when PICUs are overwhelmed.

    Apparently an editorial in JAMA concurs (according to a Medscape snip of it) – http://www.medscape.com/viewarticle/710347 -

    ” … “We have demonstrated that 2009 influenza A(H1N1) infection–related critical illness predominantly affects young patients with few major comorbidities and is associated with severe hypoxemic respiratory failure, often requiring prolonged mechanical ventilation and rescue therapies,” the study authors conclude. “With such therapy, we found that most patients can be supported through their critical illness.” …

    … In an accompanying editorial, Douglas B. White, MD, MAS, and JAMA Contributing Editor Derek C. Angus, MD, MPH, from the University of Pittsburgh School of Medicine in Pennsylvania, note that many US hospitals may be inadequately staffed to provide treatment of the most seriously ill patients with 2009 influenza A (H1N1) in a timely fashion.

    “Hospitals must develop explicit policies to equitably determine who will and will not receive life support should absolute scarcity occur,” Dr. White and Dr. Angus write. “Any deaths from 2009 influenza A(H1N1) will be regrettable, but those that result from insufficient planning and inadequate preparation will be especially tragic.” … “

  20. #20 revere
    October 12, 2009

    Don: Thanks. The Editorial comment (and the three papers) are available for free. Editorial is here: http://jama.ama-assn.org/cgi/content/full/2009.1539

    Some limitations to these data as they are not population based. I think the southern hemisphere data are better guides at the moment but they may underestimate demand. We could build in a safety factor x2 if we had good PICU bed numbers.

  21. #21 Don S
    October 12, 2009

    Thanks for the link.

    There is also this – http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2809%2961512-9/fulltext#tbl1

    Over three years in 4 UK PICUs with seasonal influenza resulted in 58 admits and 9 deaths.

    During the initial wave of swine flu in those same units there were 13 admits, “Eight of the cohort presented with shock: one was fluid-responsive, three responded to catecholamines, and four had catecholamine-resistant and steroid-resistant shock, one of which was associated with bacterial coinfection. Five children died. This fulminant course was not seen in the seasonal cohort.”

    The initial wave was only a small tip of what the coming wave is expected to be. Hard to extrapolate from this sample to a population at large.

    One wonder I still have about the Australian/New Zealand numbers is if influenza epidemics tend to be less intense there in general. 11% overall infection rate for a Winter’s worth of swine flu seems to be a smallish number. If their baseline PICU admit rate is very low then 15x it may not have overwhelmed a system, whereas 15x a larger typical baseline would.

    Still we can only work with the data we have access to.

  22. #22 revere
    October 12, 2009

    Don: I’m not confident of the overall infection rate figure of 11%. My guess is that it is higher, but the important data point is the number of admissions per million population. I calculate for the Canadian paper it is around 8 per million, a third of the southern hemisphere developed nation data. More here tomorrow morning.

  23. #23 Don S
    October 12, 2009

    I look forward to your take on it!

    Dang. A third of the admits per million as in Australia but still enough to cause “full occupancy of all regional ICU beds” at peak in the peak area. Patients “stickier” – not just in the ICU for a week but for 12d as median. And vented that long too.

    Per a news report interview – http://news.yahoo.com/s/nm/20091012/hl_nm/us_swineflu_sick_1/print
    “…Kumar said he normally sees only a few patients a year who become severely ill from an infection.

    “In the case of Winnipeg, we saw 40 people on ventilators struggling for their lives simultaneously. It’s a bizarre and somewhat frightening experience,” he said in a telephone interview.

    “At one point, 50 percent of the available ICU (intensive care unit) beds in the entire city were filled with H1N1 patients,” Kumar said. “We basically maxed out our capacity.” …”

    And this is what just the first wave did? (Albeit at peak in peak location.) And we have media idiots frightening people out of getting vaccinated…

  24. #24 Paula
    October 12, 2009

    Thanks, Don S. We also have administrative (hospital, state-level, bureaucratic communications, etc.) folks sticking their heads in the sand, especially re honest info to the public, whom half the time they regard as “difficult-acting” adversaries.