A case-control study of acute respiratory tract infection in general practice.

Background: Acute respiratory tract infections (ARTIs) cause considerable morbidity, but little is known about the presence of respiratory pathogens in asymptomatic individuals. We hypothesized that asymptomatic persons could have a subclinical infection and thus act as a source of transmission. Methods: During the period 2000-2003, all patients with ART1 who visited their sentinel general practitioner had their data reported to estimate the incidence of ART1 in Dutch general practices. A random selection of these patients (cases) and an equal number of asymptomatic persons visiting for other complaints (controls) were included in a case-control study. Nose and throat swabs of participants were tested for a broad range of pathogens. Results: The overall incidence of ART1 was 545 cases per 10000 person years, suggesting that, in the Dutch population, an estimated 900000 persons annually consult their general practitioner for respiratory symptoms. Rhinovirus was most common in case patients (24%), followed by influenza virus type A (ll%), and coronavirus (7%). Viruses were detected in 58% of the case patients, beta-haemolytic streptococci group A in 11%, and mixed infections in 3% of the cases. Pathogens were detected in about 30% of the control subject, particularly in the youngest age groups. Conclusion: This study confirms that most ARTIs are viral and supports the reserved policy of prescribing antibiotics. In both case and control subjects, rhinovirus was the most common pathogen. Of bacterial infections, only group A betahaemolytic streptococci were more common in case patients than in control subjects. Asymptomatic persons may be a neglected source of transmission. (aut. ref.