Bacterial aetiology in lower respiratory tract infections: Relevance in outpatients

Abstract

Lower respiratory tract infection (LRTI) is one of the leading reasons for consulting in primary care. Today, a general practitioner faces the challenge of distinguishing between patients with a mild self-limiting disease to whom antibiotics would do more harm than good and those who would benefit from antibiotic treatment and should be monitored closely. Two categories are generally considered relevant with regard to the diagnosis and treatment of LRTI, i.e. bacterial LRTI and pneumonia. However, the current management of LRTIs is often inadequate and involves the unnecessary prescription of antibiotics, which drives antimicrobial resistance. To contribute to the rational management of LRTIs in adults, three main topics – for which currently evidence is lacking – are discussed in this thesis: the diagnostic workup and disease course of bacterial LRTI in primary care, the effects of antibiotics on uncomplicated pneumonia and the clinical relevance of resistance in bacterial LRTIs. We analysed data on 3,104 adult primary care patients with acute cough (≤ 28 days) in 12 European countries. All of the patients underwent clinical examination, measurement of C-reactive protein and procalcitonin in blood, and chest radiography. Bacterial infection was determined by conventional culture, polymerase chain reaction and serology, and positive results were defined by the presence of Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Bordetella pertussis or Legionella pneumophila. All patients recorded symptoms in a diary for four weeks. The main results were as follows. Firstly,signs and symptoms turned out to have limited clinical value for identifying a bacterial cause in primary care patients who are not severely ill and in those who present with clinically unsuspected pneumonia. C-reactive protein measurement added little to the clinical assessment and procalcitonin added no information to the diagnostic workup of these patients. Moreover, we found that Bordetella pertussis infection was not that common among adults presenting with acute cough (3%) and that symptoms had limited diagnostic value when it came to detecting pertussis in these patients. In general, the disease course of bacterial LRTI in outpatients without pneumonia was mild, uncomplicated and self-limiting; no different from that of non-bacterial LRTI, with the exception that B. pertussis infection showed a prolonged disease course, especially regarding cough. However, in subjects with radiologically proven but not clinically suspected pneumonia bacterial aetiology seems to matter since antibiotics (oral amoxicillin) improved symptom duration and symptom severity in this subset of patients. Finally, bacterial resistance was not related to disease course. Based on these results, we concluded that in outpatients with non-severe LRTI without risk factors, the detection of bacterial pathogens is not helpful when it comes to deciding which patients should receive antibiotic treatment. Moreover information about antimicrobial resistance does not contribute. Indications for the antibiotic treatment of LRTI are related to disease severity and the patient’s vulnerability. For elderly patients, there is still insufficient evidence on bacterial infections in LRTI to withhold antibiotics with confidence. Future studies could help determine the diagnostic and prognostic value of point-of-care inflammatory tests.