The prevalence of potentially pathogenic bacteria in nasopharyngeal samples from individuals with a long-standing cough - clinical value of a nasopharyngeal sample

Background. A long-standing cough is a common cause for visits to a GP. If the patient also has a respiratory tract infection, one of the concerns of the doctor is to decide if the cough is caused by an underlying bacterial i nfection. Objectives. Our aim was to investigate whether a nasopharyngeal sample, obt ained in routine medical practice, could yield information about the aetiol ogy of a long-standing cough in patients with a respiratory tract infection . Methods. The prevalence of potentially pathogenic bacteria (Streptococcus p neumoniae, Haemophilus influenzae and Moraxella catarrhalis) in nasopharyng eal swab samples from 618 healthy individuals was compared with that from 2 36 patients with a respiratory tract infection and long-standing cough (>9 days) of the same age in a defined geographical area. Results. The proportion of cultures with potentially pathogenic bacteria de creased with age and was 44% among healthy individuals of pre-school age, 1 3% in schoolchildren and 6% in adults. The corresponding figures for patien ts with a long-standing cough were 83, 35 and 36%, respectively. All types of potentially pathogenic bacteria were found more frequently in preschool children and in adults with a long-standing cough compared with healthy ind ividuals of the same age. Conclusions. In patients with a respiratory tract infection and a long-stan ding cough, where a bacterial infection is suspected on clinical grounds, a nasopharyngeal culture could yield information about the aetiology. If M.c atarrhalis is found in pre-school children, or if H.influenzae is found in adults, they are likely to be the aetiological agent.