Inclusion Criteria:
- Subjects who the investigator believes that parent(s)/ legally acceptable representative can and will comply with the requirements of the protocol.
- A male or female child between, and including, six to 72 months of age at the time of enrolment.
- Written informed consent obtained from the parent(s)/ legally acceptable representative of the subject.
- No antibiotic therapy within four weeks prior to the visit.
- No cystic fibrosis or known major immunodeficiency such as agammaglobulinaemia, T cell deficiency or Human Immunodeficiency Virus / Acquired Immune Deficiency Syndrome.
- No documented evidence or suspicion of gastroesophageal reflux disease.
- No evidence of an upper viral respiratory infection four weeks prior to the visit.
In addition, all subjects regarded as 'cases' must satisfy all the following criteria at study entry:
- Persistent cough greater than eight weeks.
- No response to five-day prednisolone treatment.
- Chest X-ray showing no evidence of a lobar pneumonia or gross structural abnormality.
In addition, all subjects regarded as 'controls' must satisfy the following criteria at study entry:
- No respiratory symptoms four weeks prior to the visit.
- No documented evidence or suspicion of lung disease upon physical examination.
Exclusion Criteria:
- Concurrently participating in another study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational product.
- Use of any investigational or non-registered product within 30 days prior to study procedures, or planned use during the study period.
- Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
- Child in care.