The diagnosis of pneumococcal disease is difficult and microbiological proof of infection may not be possible. There are various ways of finding out whether a patient has a pneumococcal infection. Which tests are used will depend on the patient’s signs and symptoms. As other types of bacteria can also cause infections with similar symptoms, testing specifically for the presence of S. pneumoniae is important.
The doctor may carry out or order some of the tests described below:
A physical examination of the patient - the physician will listen to the patient’s chest with a stethoscope. If a distinctive crackling sound is heard (rales) it could be a sign of pneumonia. A healthcare provider may also be able to diagnose cases by observing a patient’s respiratory rate and breathing patterns.
Blood pressure test - people with serious infections tend to experience a drop in blood pressure.
Chest x-ray - a "shadow" on the chest x-ray may indicate pneumonia. There may also be evidence of fluid in the pleural cavity which may indicate empyema.
Specimen (sample) tests - if pneumococcal infection is suspected, Gram stain and culture should be performed using appropriate specimens, which should include at least one of the following:
- Cerebrospinal fluid test by lumbar puncture - a sample of cerebrospinal fluid is taken from the base of the patient’s spine and checked for bacteria. If a raised CSF white cell count and/or bacteria are found it means that the patient has meningitis.
- Pleural fluid or lung aspirate
- Joint fluid
- Peritoneal fluid
- Other abscesses or tissue specimens
Ideally, samples should be obtained before antibiotic therapy has started but there should never be a delay in starting antibiotics. Samples should be placed directly into blood-culture bottles when possible.
Laboratory tests are not usually ordered if the patient has conjunctivitis, or otitis media, unless they have an unusually high fever or appear to be extremely ill.