Pneumonia is diagnosed based on clinical evaluation and X-ray imaging when available. It can be difficult to establish whether pneumococcal infection is the cause of the patient’s symptoms because even in true pneumococcal cases, the specimens collected often do not yield the bacterium. This is particularly true of pneumococcal pneumonia because specimens from the actual site of infection (i.e., the lung) cannot be collected and in only a small fraction of pneumococcal pneumonia cases is the blood also infected.
When laboratory testing is possible, pneumococcal infections may be identified through testing of the blood (for bacteraemia and bacteraemic pneumonias) or in the case of suspected meningitis by performing a lumbar puncture, which involves inserting a needle into the epidural space to obtain a sample of cerebrospinal fluid (CSF). Pneumococcus is a difficult bacterium to grow in the laboratory and frequently goes undiagnosed even when blood or CSF samples are truly infected with the pneumococcus.. Testing to determine the pneumococcal serotype is used primarily for research purposes and is not available for patient diagnosis in most clinical settings.