# 5205
A new study this morning from the journal Clinical Infectious Diseases, but first some background:
From the earliest days of the 2009 H1N1 `swine’ flu outbreak, it was apparent that most people who contracted this particular virus experienced a mild illness, and recovered without incident.
There were exceptions, however.
A significant number of apparently healthy individuals were overwhelmed by this virus, but most who were hospitalized appeared to have various underlying risk factors (ie. pregnancy, asthma, COPD, neuro/ developmental disorders, heart failure, etc.)
Extreme (or morbid) Obesity (BMI > 40) was mentioned very early on in the outbreak as a possible risk factor, based primarily on anecdotal stories describing many of those hospitalized during the first wave of the illness.
In fact, the earliest mention I can find in this blog of the link to obesity (and smoking) came on May 25th, 2009; roughly one month after the first swine flu cases were announced in San Diego (see H1N1 Morbidity And Previously Existing Conditions).
Over the next couple of months obesity was often mentioned as a possible risk factor (see Obesity Seen As Major Risk Factor For Flu Complications) , then cautiously discounted as unproven (see More On The ACIP Meeting) in late July of 2009.
In the second half of August, 2009 we got one of the first major studies that looked at the epidemiology of swine flu patients ( see Eurosurveillance: Epidemiology Of Swine Flu Fatalities), that examined 574 deaths associated with pandemic H1N1 influenza up to 16 July 2009
Two risk factors seem of particular importance: pregnancy and metabolic condition (including obesity which has not been considered as risk factor in previous pandemics or seasonal influenza).
In November of 2009 we saw a report (see Study: H1N1 Hospitalization Profiles), again in Eurosurveillance, on the first 205 confirmed H1N1 patients hospitalized in Ireland, and it listed the following risk factors:
The most common risk factor in admission to intensive care was chronic respiratory disease followed by chronic neurological disease, asthma and severe obesity.
Morbid obesity continued to be associated with H1N1 severity over the winter, and in March of 2010 we saw a PLoS One research article - Morbid Obesity as a Risk Factor for hospitalization and Death due to 2009 Pandemic Influenza A (H1N1) Disease – followed by this update from the CDC, that added more evidence (see Morbid Obesity And H1N1 Flu).
The CDC webpage (now archived for historical purposes) read, in part:
Morbid Obesity as a Risk Factor for Hospitalization and Death due to 2009 H1N1
This document provides updated information on obesity and morbid obesity as risk factors for serious 2009 H1N1-related complications based on findings from recent studies.
How are obesity and morbid obesity defined?
Body mass index (BMI) is a measure of body fat based on height and weight. Obesity is defined as a BMI of greater than or equal to 30 kilos per meter squared and morbid obesity is defined as a BMI greater than or equal to 40 kilos per meter squared. Among Americans 20 years and older, 28% are obese and 5% are morbidly obese.
<SNIP>
Should obesity be considered a high risk condition?
Scientific findings to date, including the PLoS ONE study, support the conclusion that people who are morbidly obese are at increased risk from complications of 2009 H1N1; these individuals should get vaccinated against it and should be treated early with antivirals if they do become sick. It is unclear based on this study, however, if a casual relationship exists between obesity and severe complications from 2009 H1N1 independent of other factors.
As you can see, while it is fairly easy to make early anecdotal observations, assembling solid scientific evidence – and actually quantifying the risk - takes time.
All of which serves as prelude to a California study, embargoed until last night, that found a three-fold increase in mortality among H1N1 patients who were morbidly obese.
That report hat is available online now. Here is the press release from the IDSA, followed by the link to the paper.
Infectious Diseases Society of America
Extreme obesity associated with higher risk of death for 2009 H1N1 patients
[EMBARGOED FOR JAN. 5, 2011] For those infected with the 2009 pandemic influenza A (H1N1) virus, extreme obesity was a powerful risk factor for death, according to an analysis of a public health surveillance database. In a study to be published in the February 1, 2011, issue of Clinical Infectious Diseases, researchers associated extreme obesity with a nearly three-fold increased odds of death from 2009 H1N1 influenza. Half of Californians greater than 20 years of age hospitalized with 2009 H1N1 were obese. (Please see below for a link to the study online.)
Data from 500 adults hospitalized with H1N1 in the first four months of 2009 in California were analyzed to test the hypothesis of obesity as a risk factor for increased fatality. Extreme obesity is defined as having a body mass index (BMI) equal to or over 40. The data was collected April 20 – Aug. 11, 2009, by health providers and reported to local health departments, which subsequently provided the data to the California Department of Public Health. During this period, H1N1 accounted for 50 percent of influenza-like illnesses. Patients under 20 years of age and pregnant patients were excluded from the study.
"Extremely obese persons with a body mass index equal to or over 40 should get vaccinated annually for influenza," according to study author Janice K. Louie, MD, MPH, of the California Department of Public Health. "They should also see their health provider early if symptoms of influenza develop, so that they can get diagnosed and treated as quickly as possible. This is especially important if the influenza virus is known to be circulating in the community and causing illness." Dr. Louie stressed that more research is needed to understand why extremely obese people are more likely to die from the 2009 H1N1 influenza infection.
A Novel Risk Factor for a Novel Virus: Obesity and 2009 Pandemic Influenza A (H1N1)
Janice K. Louie, Meileen Acosta, Michael C. Samuel, Robert Schechter,Duc J. Vugia,Kathleen Harriman, Bela T. Matyas, and the California Pandemic (H1N1) Working Group
