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

Abstract

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. 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. 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. 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. 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.