Underlying conditions like asthma, diabetes, heart disease or tuberculosis appear to put swine flu victims at greater risk of hospitalization or death, doctors from the WHO and the CDC said.
Some of the serious cases involve healthy young people, and the reasons for that are still unexplained. Many of the patients went into rapid decline and died of viral pneumonia, not bacterial pneumonia, said Dr. Sylvie Briand, a W.H.O. flu expert. Viral pneumonia may be a result of the “cytokine storm,” in which the body’s own immune reaction to a new virus floods the lungs with fluid. It can progress faster and be harder to treat than bacterial pneumonia.
The cytokine storm was thought to be one of the factors that contributed to the deadliness of the 1918 pandemic. A cytokine storm describes an immune system that has over-reacted and is damaging the body, causing failure of multiple organ systems. This would explain why an unusually large number of young people died during the 1918 flu; they had the healthiest immune systems.