Managing community-acquired pneumonia during flu season
ABSTRACTThe clinical findings of influenza overlap those of community-acquired bacterial pneumonia (CABP), and influenza infection can be complicated by bacterial infections. Reviewed here are the epidemiology, pathophysiology, diagnosis, and management of community-acquired pneumonia (CAP) with special emphasis on considerations during influenza season.
KEY POINTS
- Especially during flu season, clinicians should consider influenza in patients with respiratory symptoms.
- The diagnosis of CAP is based primarily on clinical factors: a combination of signs and symptoms such as cough, fever, chills, sputum production, dyspnea, pleuritic pain, tachypnea, tachycardia, hypoxemia, consolidation or rales on auscultation, and a new infiltrate on chest imaging.
- Empiric outpatient treatment of a previously healthy patient with CABP should include either a macrolide or doxycycline. A fluoroquinolone or beta-lactam plus a macrolide should be used for patients with comorbid conditions.
- Several indices have been validated for use in deciding on inpatient vs outpatient treatment and whether a patient with pneumonia should be admitted to an intensive care unit.
DIAGNOSTIC TESTING
Once the diagnosis of pulmonary infection is suggested by clinical features, the initial evaluation should include measurement of vital signs, physical examination, and radiographic imaging of the chest. Additional diagnostic measures to consider include viral testing, blood culture, sputum culture, urinary antigen testing for Legionella and for S pneumoniae, fungal culture, and mycobacterial smear and culture.
Chest radiography (with posterior-anterior and lateral films) is the study that usually demonstrates the presence of a pulmonary infiltrate. If initial chest radiographs do not show an infiltrate, imaging can be repeated after treatment is started if the patient’s clinical presentation still suggests pneumonia. Chest radiographs are of limited value in predicting the pathogen, but they help to determine the extent of pneumonia and to detect parapneumonic effusion.46
A caveat: anterior-posterior, posterior-anterior, and lateral views can miss more than 10% of effusions large enough to warrant thoracentesis, especially when there is lower-lobe consolidation.47
Blood cultures are recommended for patients admitted to the intensive care unit and for those with cavitary infiltrates, leukopenia, alcohol abuse, severe liver disease, asplenia, positive pneumococcal urinary antigen testing, or a pleural effusion.21 However, blood cultures are positive in only 3% to 14% of hospitalized patients with CABP, and the impact of a positive blood culture on management decisions in CABP appears to be quite small.48–50
For the highest yield, blood culture results should be obtained before antibiotics are given. Not only is this good practice, but obtaining blood culture results before starting antibiotics is one of the quality measures evaluated by the Center for Medicare and Medicaid Services.51
Sputum culture is considered optional for outpatients and patients with less-severe pneumonia.21 While it can provide a rapid diagnosis in certain cases, a good-quality sputum sample is obtained in only 39% to 54% of patients with CABP, yields a predominant morphotype in only 45% of cases, and provides a useful microbiologic diagnosis in only 14.4%.52,53 Fungal and mycobacterial cultures are only indicated in certain situations such as cavitary infiltrates or immunosuppression.
Urinary antigen testing for Legionella and S pneumoniae should be done in patients with more severe illness and in those for whom outpatient therapy has failed.21S pneumoniae testing has been shown to allow early diagnosis of pneumococcal pneumonia in 26% more patients than with Gram staining, but it fails to identify 22% of the rapid diagnoses initially identified by Gram staining.54 Thus, a sequential approach is reasonable, with urinary antigen testing for patients at high risk without useful results from sputum Gram staining. Also, recent data suggest that the pneumococcal urinary antigen test may allow optimization of antimicrobial therapy with good clinical outcomes.55
Endotracheal tests. If the patient is intubated, collection of endotracheal aspirates, bronchoscopy, or nonbronchoscopic bronchial lavage (sometimes called “mini-BAL”) should be performed.
Thoracentesis and pleural fluid cultures should be done if a pleural effusion is found. Empyema, large or loculated effusions, and parapneumonic effusions with a pH lower than 7.20, glucose levels less than 3.4 mmol/L (60 mg/dL), or positive results on microbial staining or culture should be drained by chest tube or surgically.56
Testing for influenza should be done if it will change the clinical management, such as the choice of antibiotic or infection control practices. Specimens should be obtained with either a nasopharyngeal swab or aspirate and tested with reverse transcriptase polymerase chain reaction, immunofluorescent staining, or rapid antigen detection, depending on local availability.45
Inflammatory biomarkers such as C-reactive protein and procalcitonin have been receiving interest as ways to predict the etiology and prognosis of CAP and to guide therapy. Several studies have shown that C-reactive protein can help distinguish between CAP and bronchitis, with higher values suggesting more severe pneumonia and pneumonia caused by S pneumoniae or L pneumophila.57 Procalcitonin may help discriminate between severe lower respiratory tract infections of bacterial and 2009 H1N1 origin, although less effectively than C-reactive protein. Low procalcitonin values, particularly when combined with low C-reactive protein levels, suggest that bacterial infection is unlikely.58
RISK STRATIFICATION AND SITE-OF-CARE DECISIONS
Following a presumptive diagnosis of CAP, it is important to decide not only what treatment the patient will receive but whether he or she should be hospitalized. If the patient is to be admitted to the hospital, the clinician must also decide if his or her condition warrants intensive care.
Severity-of-illness scores
A recent meta-analysis compared the performance characteristics of the PSI and CURB-65 scores for predicting mortality in CAP and found no significant differences in overall test performance.61
Another meta-analysis found that the PSI was more sensitive than the CURB-65 and had a low false-negative rate, and so was better at showing which patients do not need to be hospitalized. Conversely, the CURB-65 was more specific and had a higher positive predictive value, and thus was more likely to correctly classify high-risk patients.62
Other scoring systems that aid in deciding about hospital admission and level of care include the CRB-6563 (which can be used instead of the CURB-65 if laboratory values are not available), SMART-COP,64 and SCAP.,65
Guidelines on when to admit to the intensive care unit
Guidelines from the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) also provide guidance on when intensive care admission is advised,21 and their criteria were recently validated.66 The guidelines advocate direct admission to the intensive care unit for patients requiring vasopressors or mechanical ventilation, and intensive care unit or high-level monitoring for patients with three of the following criteria for severe CAP21:
- Respiratory rate ≥ 30
- Pao2/Fio2 ratio ≤ 250
- Multilobar infiltrates
- Confusion or disorientation
- Uremia (blood urea nitrogen ≥ 20 mg/dL)
- Leukopenia (white blood cell count < 4.0 × 109/L)
- Thrombocytopenia (platelet count < 100 × 109/L)
- Hypothermia (core temperature < 36.0°C [96.8°F])
- Hypotension requiring aggressive fluid resuscitation.
None of these scoring systems or criteria is meant to replace clinical judgment. A recent study has suggested that an oxygen saturation of less than 92% is an appropriate threshold for hospital admission, in view of higher rates of adverse events in outpatients with saturations below this value.67
