Risk Factors for Severe Swine Flu a Wide Umbrella Under which Many Stand

A ProMED-mail post (June 19, 2009)

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.