What can you do to tell if a chest infection is viral or bacterial?

Infection: Culture and various serological testing can often identify the likely organism responsible for infection, and this includes the presence of antigens in urine, sputum and blood as well as antibodies. Often the clinical presentation of the illness will suggest the likely culprit, but proving it definitively may be difficult.

Chest infection : History and clinical examination do guide towards the probable cause , confirmation is possible only after culture of sputum and blood tests . http://patient.info/health/chest-infection