STONY BROOK, NY --While burn pits have been the focus of a controversy for years about causes of high rates of respiratory illnesses among military personnel deployed to Iraq and Afghanistan, evidence increasingly paints a more complex — and far more difficult to address — picture.

A new study published in the Proceedings of the National Academy of Sciences suggests that the flu virus that killed 50 million people worldwide in 1918 “circulated silently” at least four months before the 1918 influenza reached pandemic levels in the fall.

WASHINGTON — A pulmonary physician recently testified at a Senate subcommittee hearing about the number of troops returning from Iraq and Afghanistan with moderate to severe respiratory diseases, underscoring the growing debate about whether deployment to those theaters of operations increases the risk of developing lung problems.