 Less common causes of ILI include bacteria such as "Legionella", "Chlamydia pneumoniae", "Mycoplasma pneumoniae", and "Streptococcus pneumoniae".Influenza, RSV, and certain bacterial infections are particularly important causes of ILI because these infections can lead to serious complications requiring hospitalization.Physicians who examine persons with ILI can use a combination of epidemiologic and clinical data (information about recent other patients and the individual patient) and, if necessary, laboratory and radiographic tests to determine the cause of the ILI.