To minimize development and spread of antibiotic resistance, it is important to administer the correct antibacterial, by the best route, in the right amount, at optimum intervals, and for the appropriate duration.
Streptococcus pneumoniae and Haemophilus influenzae are the 2 most common bacterial pathogens observed in community-acquired respiratory tract infections.
Surveillance studies indicate increasing rates of in vitro resistance by S pneumoniae to many β-lactam and macrolide antibiotics.
To minimize risk of resistance-associated recurrence or relapse, antibacterial agents should be prescribed in accordance with existing guidelines and local resistance patterns. Patient compliance with dosage and duration of therapy should be fostered.
Preliminary data suggest that high-dose, short-course antibacterial therapy may be as effective as longer courses of low-dose therapy.
Community-acquired respiratory tract infections (CARTIs) are a reason for seeking medical attention. In 2001, there were 28.4 million office visits in the United States for an acute respiratory tract infection (excluding pharyngitis).1
Management of CARTIs poses several challenges. According to the World Health Organization (WHO), “for every 100 respiratory infections, only 20% require antibiotic treatment”2 —the remaining 80 infections most likely have a viral origin. Thus, antibacterial therapy should be avoided unless a bacterial cause has been confirmed or is deemed likely.
Once that determination has been made, clinicians need to separate patients who can be safely managed as outpatients from those who need to be hospitalized. Disease severity is, of course, an important consideration in this selection process.3-8
For management of patients who will not be hospitalized, the WHO and the Society for Healthcare Epidemiology of America/Infectious Diseases Society of America (SHEA/IDSA) offer the 3 Ds: administer the correct drug, at the right dose, and for the appropriate duration, to minimize development and spread of resistance.9,10 A recent consensus conference coordinated by the Primary Care Education Consortium and Texas Academy of Family Physicians elaborated on this mnemonic as it relates to outpatient management of 3 CARTIs: community-acquired pneumonia, acute bacterial exacerbations of chronic bronchitis, and acute bacterial rhinosinusitis. Its recommendations, which have been drawn largely from existing evidence-based guidelines, form the basis for this review.
Drug selection
Treatment with an antibacterial agent will not be medically warranted in the majority of patients with a CARTI. Many of these patients will, however, expect to go home with an antibiotic prescription. The primary care clinician can reduce such expectations and prevent unnecessary reconsultations by briefly addressing four issues: 1) the natural course of the viral illness, 2) the lack of effectiveness of antibiotics, 3) the problem of antibiotic resistance, and 4) the side effects of antibiotics.11
When selecting an antibacterial agent for patients with pneumonia, bronchitis, or rhinosinusitis for which a bacterial cause has been identified or deemed likely, several factors need to be taken into account, including the suspected or identified pathogens, local resistance patterns, previous therapy, patient allergies, and the patient’s ability to tolerate treatment failure. Many of these factors are considered by professional organizations that regularly develop guidelines for CARTIs based on the best available evidence. Perhaps most critical for decision-making in the primary care setting is an understanding of evolving microbiology and resistance patterns.
Common pathogens
There is considerable overlap among pathogens commonly found in CARTIs. Streptococcus pneumoniae and Haemophilus influenzae are most often observed in the outpatient setting.
Community-acquired pneumonia. In outpatients with mild illness, S pneumoniae, Mycoplasma pneumoniae, Chlamydia species (particularly Chlamydia pneumoniae, now called Chlamydophilia pneumoniae), and H influenzae are the most common pathogens.12,13 In patients younger than 50 years without significant comorbidity, Mycoplasma species are the most common pathogens. Older patients and those with significant comorbidity are more likely infected with S pneumoniae,13 a Gram-negative enteric bacillus, Pseudomonas aeruginosa, or Legionella.5,14
Bacterial bronchitis. In addition to S pneumoniae and H influenzae, Moraxella catarrhalis is a frequent pathogen in bacterial exacerbations of chronic bronchitis.15P aeruginosa and other Gram-negative bacilli are also seen, especially in patients with a severe acute exacerbation who have a forced expiratory volume in 1 second (FEV1) of 35% of predicted or less.16 Infection due to multiple pathogens occurs in a small percentage of all patients with chronic bronchitis, particularly those with severe exacerbations. Fewer than 10% of acute exacerbations are due to an atypical bacterium, usually C pneumoniae. M pneumoniae and Legionella pneumophila are implicated even less frequently.15
Bacterial rhinosinusitis.S pneumoniae and H influenzae also are frequent causes of acute bacterial rhinosinusitis. Other pathogens commonly seen in this condition include other Streptococcus species, M catarrhalis, oral anaerobes, Staphylococcus aureus in adults, and M catarrhalis, Streptococcus pyogenes, and anaerobes in children.17
