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.