Effect Measure

Nursing homes (Long Term Care Facilities, LTCFs) are a favorite hunting ground for respiratory viruses, including flu. They are open to the general community, where visitors and employees mingle freely with the residents. The residents are usually of an advanced age, have other sicknesses that make them vulnerable and often have less active immune defenses. So when the swine flu pandemic began at the end of April, the Public Health Laboratory at Ontario’s Agency for Health Protection and Promotion ramped up their respiratory infection outbreak registration system with the prospect that LCTFs would be hard hit. We now know that swine flu acts like other pandemic flu viruses and preferentially targets the young. This doesn’t necessarily mean the elderly are spared, however. It’s just that they are expected to suffer proportionately less than seasonal flu, which ordinarily spares the young. What adds interest to the results of the LTCF surveillance between April 20 and June 12, 2009 (roughly the first 2 months of the swine flu pandemic) is that technology was deployed to identify most of the viral agents causing respiratory disease outbreaks in the Ontario LTCFs, not just swine flu or even influenza in general.

Even a relatively simple study of this type has a number of moving parts that non-epidemiologists are usually unaware of. For example, if you are going to study outbreaks in LTCFs, you need to have a definition of an outbreak:

Respiratory infection outbreaks in LTCFs were defined as any of the following: 2 cases of acute respiratory tract illness, 1 of which was laboratory-confirmed; 3 cases of acute respiratory tract illness within 48 hours in a geographic area (e.g., unit, floor); and >2 units having a case of acute respiratory illness within a 48-hour period. Influenza-like-illness was defined as acute onset of respiratory illness with fever and cough with >1 of the following: sore throat, arthralgia, myalgia, or prostration. (Marchand-Austin et al., Emerging Infectious Diseases 2009 Dec; [Epub ahead of print])

Using this definition, 112 outbreaks were registered with the authorities after start of the pandemic, but testing couldn’t be done in 29 because of an insufficient or inappropriate sample, leaving 83 outbreaks, of which the paper reports 91% were in LCTFs (we note that 91% of 83 is not a whole number, nor does it round to 91% for any whole number; oh, well). 5% of the outbreaks were in hospitals, child care centers and psychiatric institutions, while the nature of the institutions in 4% of outbreaks was unknown. The paper reports the median age of the persons tested to be 85, with 95% older than 57. It’s not clear if this is all specimens or just the ones from LCTFs. So the data reporting is not as clear as it might be. This is annoying but we don’t think it affects the main message of the paper. Either way, this is an old population (the mean was 82 years, so it was not badly skewed, as the 95%-ile indicates).

The 112 outbreaks were ones that occurred after the start of the pandemic, but molecular testing was also one on a total of 589 specimens taken from 161 outbreaks that went back to the start of the flu season. This was not as intensive testing as occurred in response to the pandemic, but gives a picture of the just concluded seasonal flu season. What was interesting was that use of a multivirus molecular panel allowed the lab to identify an agent in 89% of these 161 outbreaks, an astonishingly high number. Most (69%) of the outbreaks were caused by a single agent (not always the same one), but 15% of the outbreaks involved two different viruses simultaneously, while 4% involved there viruses. There were even 2 outbreaks that have 4 simultaneously pathogenic agents involved in the outbreak! The epidemiology of respiratory outbreaks in LTCFs (and probably in all institutions) is can be much more complex than we usually assume.

The most common respiratory virus was enterovirus/rhinovirus, usually associated with upper respiratory infections (“head cold”), but especially in LTCFs capable of producing fatal lower respiratory infection. Other viruses (in order of prevalence) were metapneumovirus (which we once posted on here), parainfluenza virus and influenza A/H1. 186 patients (as opposed to outbreaks) had no virus identified, which means that there might be even more variety and multiple agents in some outbreaks than identified. But it wasn’t just outbreaks that had multiple agents. 22 patients had co-infections with more than one virus, most commonly two different types of coronavirus.

What about swine flu? There were two swine flu outbreaks, but it appears only the first to occur (June 3) was in a LTCF (the other was in a hospital treating patients with influenza-like illness). The date is significant because by that time swine flu was reported to be widespread in the general community, with over 2000 cases confirmed at the public health laboratory in that time period. No seasonal H1N1 was detected in any of the institutional outbreaks and largely absent from community.

In addition to the general interest of what kind and how many viruses cause LTCF outbreaks, these data confirm dramatically what we already knew: that the elderly are not the target of swine flu, the younger age groups are. Exactly why this is we don’t know. The two leading explanations involve some residual immunity from the days prior to 1957 when the 1918 lineage H1N1 seasonal flu was replaced by H2N2 (the “Asian flu”), but a seasonal H1N1 made a comeback in 1977 and has since been co-circulating with H2N2’s successor in the 1968 pandemic (the “Hong Kong flu”). Why that virus affords no cross-protection if the residual immunity explanation is correct remains to be explained. A second explanation is the relative lack of contact between the older segment of the population and the likely human vector of swine flu (those under the age of 20). That may well play a part, but it doesn’t feel convincing to us. The sparing of the older age group (for which we are grateful) is one of the intriguing mysteries of this pandemic.

Meanwhile, it puts us older folks at the end of the line for swine flu vaccine. Personally, I don’t mind and see the rationale for that, but it wasn’t exactly something we as a society discussed and decided. That’s our fault. For years bioethicists have been pleading for a national conversation on how to use scarce resources in an emergency but we haven’t done it. So now the decision has been made, as it had to be, without benefit of as much public participation as we would have liked.

Life is like that. And so is death.

Comments

  1. #1 Dr Denise
    November 10, 2009

    Revere
    Well said, objectively and compassionately. I am a bit more depressing on this issue, please be forewarned. I have a few elderly friends and patients who feel the current culture/administration no longer needs them, that they are at the back of the line on things like this. One couple I know in their 80’s are quite hurt that they are “low priority” for the vaccine. They are lifelong military and have helped out in several wars here and feel betrayed. The others I know seem ready to die to not be a burden (not related to swine flu but the economy). One has already passed, almost on cue, as her monies ran out in the market crash and she had no desire to be on the state tab.

    There are consequences to these unspoken messages, and so it goes. There are no easy or good answers to rationing of potentially life saving resources. But those left out do notice the trends. I myself am top priority HCW, still cannot get inactivated vax here in NYC. Would prefer to avoid flumist as I treat many immunocompromised adults.

  2. #2 jbh
    November 10, 2009

    We can’t even have a rational, constructive national conversation on healthcare reform, I don’t know how we could ever have a national conversation about something as tricky as how to use scarce medical resources.

  3. #3 Paula
    November 10, 2009

    Very good discussion, revere. I’m curious what you meant, re “the relative lack of contact between the older segment of the population and the likely human vector of swine flu (those under the age of 20)” as an explanation “doesn’t feel convincing to us”; your feeling here may be good intuition, but can you clarify?
    I share Dr Denise’s depression on this issue, and not only as an older person or even a friend of several older HCW persons who nevertheless are by age last in line (and if the [so far]“lack of contact” theory is the correct one, are by no means safe).
    The casual view of old persons as irrelevant no-longer-persons has been extant in this country for at least decades, and can hardly be attibuted to the current administration’s policies–yet it is hard not to wonder. That those least at risk should be last for a scarce vaccine makes sense; that trimming of “waste” from Medicare should be a main component to pay for expanded health coverage makes, if not necessarily factual, at least political sense; when one looks at both, though, in conjunction with the swarm of recent popular articles lauding strictly palliative care for, specifically, elderly patients in their last months(a preference one may prefer for oneself, but preferably to be determined by a person’s choice and not by economic policy); then one does start to note a message. Yes, it is a message riding, in part, on the wheel of time; it seems, however, to be rolling in on politico-economic wheels as well.

  4. #4 red rabbit
    November 11, 2009

    Interestingly, this year’s seasonal flu vaccine, Vaxigrip, also has the seasonal lineage H1N1 as a component. I find it odd that there seems to be no cross-protection.

    It’s been difficult here in Ontario where public health (understandably, considering how quickly things were moving) jumped when the news outlets got hold of that paper which supposedly suggested that those who had received last year’s Vaxigrip were at increased risk of pandemic-strain flu this year. We were told to cancel our flu clinics in favour of H1N1 and everything was rearranged entirely by the time the paper with its true, not-mangled-by-the-media result was released 3 days later. Obviously, there was no increased risk.

    On the up side, that shows how quickly public health is willing to respond. On the downside, Oh, the confusion! Today I saw a couple: he was over 65, and so is not yet eligible for the H1N1 vaccine, but can get his seasonal flu shot. She was under 65 but not “high risk” so we have no H1N1 vaccine for her though she will be eligible when the supply becomes available, and we have been asked to delay the seasonal flu shot for these patients.

    Plus based on a study on measles vaccine done in 1965 we are asking people to wait three weeks between shots. Imagine trying to explain all of this. Hours of entertainment!

  5. #5 Alex Marchand-Austin
    November 19, 2009

    In response to your comments about the numbers, 75 out of 83 outbreaks were from LTCFs. This is 90.36% and was rounded to 91% for formatting purposes.

    With regards to the mean and median age, these reflect all patients from institutional outbreaks registered between April 20 and June 12, 2009. Not just those from LTCFs.

  6. #6 revere
    November 19, 2009

    Dr. Marchand-Austin: Many thanks for clarifying those minor details. As we noted, the main points were unaffected.

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