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Acute respiratory tract infections (RTIs), both upper (URTIs) and lower respiratory tract infections (LRTIs), are the most common reason for consultation with a general practitioner.RTIs result in about 180 million antibiotic prescriptions per year in the EU-27 member states (ESAC website, 2008; www.esac.ua.ac.be), and 6.4 million antibiotic prescriptions were prescribed for acute bronchitis and cough in 2003 in adults between 16 and 64 years old in the United States (65).The number of pathogens involved in LRTI, with various susceptibilities to antimicrobials, is large constituting an enormous challenge for diagnostic microbiology.In general, in only 50% of cases is an etiologic agent detected.Documented infection is uncommon in community-managed infection and is usually only defined in 25 to 50% of hospital-managed infections.The upper end of the respiratory tract, the rhinopharynx, is widely open to the introduction of airborne microorganisms.It is, however, also a very efficient barrier for invading bacteria.The barrier function of the rhinopharynx results from the local lymphoid tissue producing phagocytic cells and secretory immunoglobulin (Ig) and from the rich commensal flora of aerobic and anaerobic microbes establishing an interfering colonization resistance.The number of these organisms varies from 2.6 ϫ 10 4 to 4 ϫ 10 8 CFU of cultivable bacteria per cm 2 (95).Aerobes tend to decrease and anaerobes tend to increase with age (98).Colonization starts during the first year of life and is composed not only of commensal organisms but also of potential pathogens: group A -hemolytic streptococci, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.These are present permanently or intermittently, with rates varying with age (decreasing in adults), exposure to other children, geographic location, socioeconomic status, and vaccination status (39).In most cases, these organisms cause disease in only a small percentage of persons colonized.Viruses do not normally colonize the rhinopharynx.However, most bacterial
Loens et al. (Thu,) studied this question.