The flu season has barely begun, and already hospitals are feeling a strain on their capacity. Last week, the CDC declared the outbreak to be an epidemic by one measure. “We’re seeing an onslaught of patients, to be honest. We’re seeing much higher volume than in previous years,” said Dr. Robert Kelly, president of New York-Presbyterian Hospital. At least one analyst said the strong flu season could be a positive for cash flow, though it may not necessarily mean higher margins for hospitals.