In the present case series, bacterial infection rate at presentation was low. Previous reports showed incidence of secondary superinfection by Streptococcus Pneumoniae, Staphylococcus Aureus, Pseudomonas Aeruginosa, Acinetobacter Baumannii, Escherichia coli [1, 3, 2] . In our experience, we found two cases (16.7%) of co-infection with Legionella Pneumophila, which is, to the best of our knowledge, a new epidemiological data, since no other case has been reported in literature. It is questionable whether Legionella Pneumophila infection occurred before or after H1N1 pneumonia. However, it could be that H1N1 pneumonia was associated with a lower reactivity of the immune system, as suggested by the low leucocytes count reported in our sample and by other Authors [3, 2, 1] .