A strong index of suspicion is required for diagnosis, especially in elderly and immunocompromised individuals, who have altered response mechanisms. This is true with “typical agents.” Subtle clues in the elderly include changes in mentation, confusion, and exacerbation of other illnesses. The febrile response may be entirely absent, and the results of the physical examination are not predictive of pneumonia. In high-risk groups, an increased respiratory rate of greater than 25 breaths per minute remains the most reliable sign of infection. Mortality in these high-risk groups of patients is strongly correlated with the ability of the host to mount normal defenses to the symptoms of fever, chills, and tachycardia.
All women suspected of having pneumonia should undergo chest radiography to establish the diagnosis and to detect alternate diagnoses such as congestive heart failure and tumors.
The chest radiograph can detect complications like pleural effusions and multilobar disease. Laboratory studies helpful in identifying community-acquired pneumonia are sputum Gram stain, sputum culture, and two sets of blood culture. An “adequate sputum” sample (defined as more than 25 neutrophils with less than 10 epithelial cells per low-powered field on microscopic examination) may be difficult to obtain. Respiratory therapists are an excellent resource for inducing sputum. Hospitalized patients undergo assessment of blood–gas exchange by either oximetry or arterial blood–gas analysis. Diagnosis of Legionella pneumoniae requires a different laboratory technique: measuring urinary antigen levels. Mycoplasma pneumoniae should be suspected when cold agglutinin findings are positive in the presence of the appropriate clinical symptoms.
The American Thoracic Society updated their original guidelines in 2001 (10). These clinical recommendations use an evidence-based approach for the diagnosis and management of community-acquired pneumonia. Therapy should be directed at the responsible or most likely pathogen, but in many cases of pneumonia, the exact cause cannot be determined, and empiric therapy should be initiated. The American Thoracic Society recommends empiric therapy based on four groups of specific patient profiles, the presence of modifying factors, and pneumonia severity (Table 9.1).
Group I. Outpatients with no cardiopulmonary disease (congestive heart failure or COPD) and no modifying factors. These patients are in the lowest-risk group and are usually infected by pathogens such as Chlamydia pneumoniae, Mycoplasma pneumoniae, or Streptococcus pneumoniae. Patients should be treated with an advanced generation macrolide such as azithromycin, clarithromycin, or doxycycline.
Group II. Outpatients with cardiopulmonary disease or modifying factors. Patients in this group usually have some comorbidities and are older than 50 years of age. Aerobic gram-negative bacilli, mixed infections with atypical pathogens, and drug-resistant
S. pneumoniae (DRSP) should be considered in this patient population. Drug recommendations include monotherapy with an antipneumococcal ﬂuoroquinolone, such as gatiﬂoxacin or levoﬂoxacin; a combination of a macrolide (or doxycycline) with a betalactam such as cefpodoxime, cefuroxime, or amoxicillin-clavulanate; or parenteral ceftriaxone followed by cefpodoxime.
Table 9.1 Modifying Factors that Increase the Risk of Infection with Specific Pathogens
Beta-lactam therapy within the past 3 months
Immune-suppressive illness (including therapy with corticosteroids)
Exposure to a child in a day-care center
Corticosteroid therapy (>10 mg of prednisone per day)
Broad-spectrum antibiotic therapy for >7 days in the past month