Acute bronchitis in adults. How close do we come to its aetiology in general practice?

Objective: To investigate how close we can come to the aetiology of acute bronchitis in adults in a primary care setting.
Design: Prospective study.
Setting: General practice population in Gardabaer district, south-western Iceland.
Subjects: 140 patients > or = 16 years old who were diagnosed as having acute bronchitis during a two-year period (1992-1993).
Main Outcome Measures: Laboratory investigations (twice with a minimum four-week interval), used in general practice to analyse respiratory tract infections. They included serology for Chlamydia pneumoniae, Mycoplasma pneumoniae, respiratory tract viruses, and the level of C-reactive protein.
Results: Of a total of 140 patients, two blood samples were taken on scheduled time in 113 patients. Serology confirmed recent infection in 18 (16%) of these patients. Only two (2%) had a bacterial infection (one C. pneumoniae, one M. pneumoniae). The others (84%) did not have a significant increase in antibody titres. Only four (4%) had C-reactive protein levels higher than 48 mg/l.
Conclusions: The study indicates that it is difficult to come close to a precise aetiology with respect to infectious agents of acute bronchitis in general practice. We conclude that the disease is rarely caused by atypical bacteria such as C. pneumoniae and M. pneumoniae, and rarely caused by bacterial infections severe enough significantly to increase the level of C-reactive protein.