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

Abstract

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 infection. OBJECTIVES: Our aim was to investigate whether a nasopharyngeal sample, obtained in routine medical practice, could yield information about the aetiology of a long-standing cough in patients with a respiratory tract infection. METHODS: The prevalence of potentially pathogenic bacteria (Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis) in nasopharyngeal swab samples from 618 healthy individuals was compared with that from 236 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 decreased with age and was 44% among healthy individuals of pre-school age, 13% in schoolchildren and 6% in adults. The corresponding figures for patients with a long-standing cough were 83, 35 and 36%, respectively. All types of potentially pathogenic bacteria were found more frequently in pre-school children and in adults with a long-standing cough compared with healthy individuals of the same age. CONCLUSIONS: In patients with a respiratory tract infection and a long-standing cough, where a bacterial infection is suspected on clinical grounds, a nasopharyngeal culture could yield information about the aetiology. If M.catarrhalis is found in pre-school children, or if H.influenzae is found in adults, they are likely to be the aetiological agent.