In my Masters thesis, I used a technique called multivariate logistic regression analysis. This was during the time of 2009 H1N1, and I looked at all the data for the Las Vegas valley, and literally went through paper patient charts looking at their demographics. I must have had 30 variables and more than 6000 hospitalized H1N1 cases, and my question was: What is the difference between hospitalized patients who tested positive for H1N1, and patients that were put into the ICU. I found that very young and very old age, cancer treatment, pregnancy, etc. were factors that made a person more susceptible to H1N1 severe illness.
I hope this answers your question!