A groundbreaking research has found obesity to be a possible contributing factor in fatal swine flu cases.
A team from the French Institute for Public Health Surveillance examined the characteristics of 574 deaths associated with the pandemic H1N1 influenza up until the middle of July.
The underlying disease was found in at least half of all fatal cases.
Mortality patterns were in many cases similar to those associated with normal, seasonal flu. However, the team observed: "Nevertheless two risk factors are noticeable: pregnancy and obesity."
Pregnancy is already a well-documented risk factor in seasonal influenza and in previous pandemics.
The researchers found that 16 women - representing 10 percent of all female deaths that were studied - were pregnant or had recently delivered at the time of their death. Half of these also had other health issues.
However, the conclusion that obesity may be a factor in some swine flu deaths opens up a new line of investigation for epidemiologists.
Where an underlying disease was found to be present after someone had died of swine flu, in more than one in four cases the deceased had a metabolic condition - diabetes and/or obesity.
The researchers also found significant demographic variations among those affected by the pandemic.
"Compared to younger age groups, the elderly seem to be protected from infection to some extent, perhaps due to previous exposure to strains akin to influenza A(H1N1)v virus," the Guardian quoted the authors as saying.
The research has been published in medical journal Eurosurveillance.