INFLUENZA A (H1N1) - WORLDWIDE (70): RISK FACTORS
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A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Thu 18 Jun 2009
Source: Google news,The Canadian Press report [edited]
Risk factors for severe swine flu a wide umbrella under which many stand
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Whether speaking of a 58-year-old man or a 38-year-old woman, or a
little boy of 9, officials announcing swine flu deaths are almost
always quick to note "underlying health conditions" may have
contributed to the fatal outcome. Asthma, heart disease, diabetes,
maybe even obesity are among the conditions used to help explain why
swine flu infection is hospitalizing and killing younger people,
people who would be expected to make a full recovery from seasonal
flu.
It could create the impression that only the sickly are dying from
the new H1N1 flu virus -- a claim no one is making. To the contrary,
many, including the World Health Organization, say between one-third
and one-half of swine flu deaths have occurred in people who were
previously healthy. But how healthy is previously healthy? The answer
depends on who you ask.
Dr Anand Kumar is a critical care specialist who has been treating
swine flu cases in embattled intensive care units (ICU) in several
Winnipeg hospitals. He says a small portion of the ICU patients look
like flu's typical victims, people with health conditions know to be
badly exacerbated by a bout of influenza. But more are younger and --
until they got sick -- healthier than flu patients hospitals
typically see during a regular influenza season. "For the most part,
these young, relatively healthy people aren't marathon runners or
anything like that," he admits. "They're normal people.... If you
asked them 'Are you healthy?' they'd say 'Yeah, pretty healthy."'
Dr Michael Gardam, head of infectious disease prevention and control
for Ontario's public health agency, believes the constant refrain of
"underlying conditions" bespeaks a sort of wishful thinking, an
attempt to explain away the unusual age range of the people the new
virus is sending to hospital or to the morgue. "That's the story that
I think people haven't really registered," says Gardam. "We're
clinging to these 'Oh, they had underlying illness, therefore it's
OK."' "But ... I would argue that the 30-year-old with mild asthma --
how big of an underlying illness is that compared to again the
80-year-old person with bad lung disease from smoking, who's got
heart disease? That's the usual group that unfortunately gets really
sick with flu, not this healthy adult group." You'll find little
argument that this virus, at this time, is causing more severe
disease in people far younger than those normally hospitalized and
killed by flu or its complications in a typical flu season.
"This is not a disease of older adults. There's no question," says Dr
Allison McGeer, an influenza expert with Toronto's Mount Sinai
Hospital. "For people under 50, this is a significantly more severe
disease than seasonal flu. For people over 50, it's much better," she
notes. But are the people under 50 who are being badly hit by the
virus specimens of perfect health or are many of them already shaded
by the broad umbrella known as "pre-existing health conditions?" How
you view a condition like asthma -- seen in 41 per cent of the
hospitalized cases in New York City -- may influence how you answer
that question. "A lot of that is about labelling people," McGeer
admits. "Half of me doesn't want you to think you're diseased if you
have asthma, and the other half of me wants you to get your flu
vaccine because you're at increased risk." "How do you walk that
line?"
Year in and year out, public health authorities get plenty of
evidence many people who have some health issues plunk themselves
firmly on the "healthy" side of the divide. Scans of people with
asthma, diabetes and other conditions, and women who are pregnant
forego the flu shots public health officials urge them to get,
suggests Dr Scott Harper, an influenza expert with New York City's
Department of Health. New York City has had one of the biggest swine
flu outbreaks to date. As of Tuesday [16 Jun 2008], more than 700 New
Yorkers have been hospitalized with swine flu and 23 people in the
city have died from infections. With those kinds of numbers, one
might expect to see patterns emerge. But Harper says in fact the
department believes that many of the health conditions known for
years to increase the risk posed by flu are being seen in the people
suffering serious disease with swine flu. "The majority of deaths
that are being seen have well recognized underlying health risks," he
insists. "Those that don't may have and we just haven't seen them
yet. And then we may also find new risk factors, but they have not
yet been adequately described analytically to be able to say it's a
legitimate risk factor."
One such potential new risk factor is obesity. An early study from
the US Centers for Disease Control suggested it may be contributing
to poor outcomes in people who contract the new H1N1. The WHO is
concerned about that possibility. "Obesity is now a huge global
problem," says Dr Nikki Shindo, an expert with the WHO's global
influenza program. "And if obesity is a risk factor, then I would be
very much worried about some of the populations that are living with
obese conditions." Four of the people who died in New York City were
obese. Still, Harper says it's too soon to say whether that's a risk
factor in and of itself, or if some of the things that go
hand-in-hand with obesity -- like early heart disease, like diabetes
-- are the real risk factors. Teasing out that answer will be tough
but necessary, he says, noting that knowing who is truly at the most
risk from this virus will dictate who stands where in the queue for
swine flu vaccine once it becomes available and who should get
priority access to antiviral drugs.
[Byline: Helen Branswell]
--
Communicated by:
ProMED-mail Rapporteur Mary Marshall
[In the absence of clearly defined risk factors it remains reasonable
to assume that older people have some degree of protection due to
earlier exposure to an immunologically similar agent. In which case
it would be appropriate to give younger age groups priority for
vaccination with a swine-origin A (H1N1)-type vaccine when available,
and to continue vaccination of older age groups with seasonal
influenza vaccine if still available. - Mod.CP]
[The article above is a timely discussion on the issue of identifying
risk factors associated with more severe disease in this current wave
of influenza A (H1N1). One factor that should be highlighted when
discussing any comparisons with prior pandemic influenza patterns is
that it has been 41 years since the last influenza pandemic (the
"Hong Kong flu" in 1968), and much has changed in the interval since
the last pandemic in terms of basic health conditions. For example
there has been an observed pandemic of obesity, so that if obesity
has always been a risk factor for more severe disease with influenza
infection, the number of individuals at risk may have crossed a
threshold now allowing the "tip of the iceberg" to be large enough to
be seen. Another change has been an increase in morbidity and
mortality due to asthma in many countries. In the USA prevalence
rates of asthma have increased since 1978 (in table 7 of the American
Lung Association 2005 report on 'Trends in asthma morbidity and
mortality,' the reported asthma prevalence rates per 1000 population
in the 18-44 year old age group went from 29.0 in 1982 to 56.9 in
1996. For full report with all tables and analyses, see
For the reverse side, in studies addressing risk factors for
influenza among children, asthma has fairly consistently been
identified as a key risk factor for disease and co-morbidity among
hospitalized cases (see refs 1 and 2 below). Pregnancy has been
observed to be a risk factor of serious disease in many viral
infections, so it is not surprising that it is showing up as a risk
factor for serious disease in this present pandemic. Excess deaths
were observed among pregnant women in the 1918 pandemic and the 1957
pandemic (see refs 3 and 4.) Widelock, Csizmas, and Klein present an
analysis of the excess mortality among pregnant women in New York
during the 1957 pandemic period when compared with the same influenza
periods in 1958, 1959, and 1960.
This moderator has been leaning towards the question of "how healthy
are those who are reportedly healthy" or are there underlying
conditions that had not previously been identified in the reportedly
"otherwise healthy" individuals who have had severe disease
associated with influenza A (H1N1) infection? Having worked in major
inner city emergency rooms in a large urban center in the USA, it was
not uncommon for individuals to present with later stage severe
disease associated with chronic illnesses that had previously not
been identified, yet had most likely been present for a significant
amount of time prior to presentation to the health sector. Often it
was co-morbidity with an acute disease that precipitated presentation
to the emergency room where the "underlying disease" was then
identified.
As for the observation that there is more disease and more serious
disease attributable to influenza A (H1N1) infection among younger
age groups, the explanation for this observation may either reflect a
cross over immunity in older age groups from previously circulating
H1N1 influenza viruses, or it may reflect the bias that the initial
age group affected were younger ages, and these cohorts have greater
co-mingling to facilitate transmission among them, or most likely, a
combination of both. A study on serum cross reactive antibody
response to the novel influenza A (H1N1) virus after vaccination with
seasonal influenza vaccine revealed at baseline, cross-reactive
antibody was detected in 6-9 percent of those aged 18-64 years and in
33 percent of those aged greater than 60 years (see ref 5 below),
demonstrating that the younger age groups were more uniformly
susceptible to infection with influenza A (H1N1). Given this
observation it appears prudent to include younger age groups in
vaccination activities, but with only one third of older age groups
with cross reactive antibodies, they should also be included as
targeted for vaccination activities. Hence, a significant challenge
for vaccine production.
This is the 1st time that pandemic influenza activity has been
subjected to such intense scrutiny under a myriad of different
microscopes (both literally and figuratively) in a prospective manner
and the medical community is there validating and disproving many
previous "observations" and "theories." There is a lot to be learned,
and as each answer becomes available, new questions arise.
References
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1. Samransamruajkit R, Hiranrat T, Chieochansin T, Sritippayawan S,
Deerojanawong J, Prapphal N, Poovorawan Y: Prevalence, Clinical
Presentations and Complications among Hospitalized Children with
Influenza Pneumonia. Jpn J Infect Dis., 61(6): 446-9, 2008. Available
from
2. Gordon A, Ortega O, Kuan G, Reingold A, Saborio S, Balmaseda A,
Harris E: Prevalence and Seasonality of Influenza-like Illness in
Children, Nicaragua, 2005-2007. Emerg Infect Dis [serial on the
Internet]. 2009 Mar [date cited]. Available from
3. Widelock D, Csizmas L, Klein S: Influenza, Pregnancy, and Fetal
Outcome. Public Health Rep 1963; 78: 1-11 Available from
4. Gall SA: Influenza and current guidelines for its control. Infect
Dis Obstet Gynecol 2001; 9: 193-5. Available from
5. Serum Cross-Reactive Antibody Response to a Novel Influenza A
(H1N1) Virus After Vaccination with Seasonal Influenza Vaccine. MMWR
Morb Mortal Wkly Rep 2009 May 22; 58(19): 521-4. Available from
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...................................cp/mpp/mj/lm
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