Pneumonia caused by S. aureus differed from the healthy controls for all 11 cytokines and in general the level of cytokines detected in influenza patients was consistently lower than the levels in patients with bacterial pneumonia and only differed from healthy volunteers for IFNγ, IL-6, IL-18, eotaxin, IP-10 and MCP-1. Here, IL18 is linked to susceptibility to pneumonia measurement.