Overview Of Pneumonia Health Article

Because the microbiologic etiology of community-acquired pneumonia is determined in only approximately 50% of cases and because this diagnosis may take a day or two, the clinician must institute appropriate empirical therapy based on the most likely agents contributing to the lung infection. When possible, empirical therapy should be initiated within 8 hours of diagnosis, an interval that appears to reduce the 30-day mortality. Empirical antimicrobial therapy is based on the severity of illness (inpatient or outpatient settings) and should broadly cover the most likely organisms. Therapy can be narrowed later based on any relevant culture information.

Effective guidelines for initial empirical therapy of community-acquired pneumonia target the most common pathogens and lead to better clinical outcomes compared with therapies not based on such guidelines (Table 92-1). The most common bacterial pathogens are S. pneumoniae and H. influenzae ; however, the so-called atypical pathogens, including M. pneumoniae , C. pneumoniae , and Legionella species, can be the primary or co-infecting agents in up to 40% of community-acquired pneumonia and must be covered in empirical antibiotic regimens.

Under current guidelines, patients are stratified with respect to where treatment is initiated (outpatient, inpatient, or intensive care unit [ICU] setting), the presence of underlying cardiopulmonary disease, and other modifying factors, such as whether the patient is likely to be infected with drug-resistant S. pneumoniae , gram-negative enteric bacilli, or P. aeruginosa . In general, outpatients who are mildly ill and without underlying cardiopulmonary disease or other modifying factors are usually infected with S. pneumoniae , M. pneumoniae , C. pneumoniae , H. influenzae , respiratory viruses, or Legionella species. These uncomplicated outpatient cases can be managed with an advanced generation macrolide, such as azithromycin or clarithromycin, which are better tolerated and have better coverage of Haemophilus than does erythromycin. ² Alternatively, doxycycline can be used in patients who are intolerant of macrolides, although this is less optimal because increasing levels of tetracycline resistance are being observed in S. pneumoniae isolates. Patients who also have underlying cardiopulmonary illnesses or modifying factors are more likely to be infected with drug-resistant S. pneumoniae or M. catarrhalis ; such patients should be managed initially not only with a macrolide or doxycycline but also either with an extended spectrum oral β-lactam (such as cefpodoxime, cefuroxime, high-dose amoxicillin, amoxicillin-clavulanate) or with parenteral ceftriaxone followed by oral cefpodoxime. Alternatively, single agent treatment can be instituted with an antipneumococcal fluoroquinolone, such as levofloxacin, gatifloxacin, or ciprofloxacin.

The decision to admit a patient to the hospital must be made on clinical grounds. Patients can be effectively and safely managed as outpatients if they are mildly ill, are younger than age 50 years, and do not have coexisting cardiopulmonary disease, malignancy, immune compromise, or renal, liver, or other significant systemic diseases. ² Features such as a respiratory rate greater than 30 breaths/minute, a diastolic blood pressure less than 60 mm Hg, evidence of poor perfusion or end-organ dysfunction (e.g., confusion or an elevated blood urea nitrogen or creatinine level), multilobar disease on the chest radiograph, or hypoxemia predict a more severe course and generally require inpatient management. Inpatients who do not require intensive care but who have underlying cardiopulmonary disease or are elderly are at risk for infection with enteric gram-negative bacteria. Such patients should be managed initially with intravenous β-lactams (i.e., cefotaxime, ceftriaxone, ampicillin/sulbactam) plus either an intravenous macrolide or doxycycline to cover atypical organisms. ³ Alternatively, an intravenous antipneumococcal fluoroquinolone may be used alone. ⁴ Patients who require hospitalization but not intensive care may be treated initially with intravenous azithromycin alone or may be started on doxycycline plus a β-lactam if they cannot tolerate macrolides. Alternatively, such patients can again be managed empirically with intravenous antipneumococcal fluoroquinolone monotherapy.

Patients who have respiratory insufficiency, septicemia, or significant multiorgan dysfunction require management in an ICU and evaluation to exclude infection with P. aeruginosa . High-risk patients include those with structural lung disease (particularly bronchiectasis), greater than 10 mg/day of previous corticosteroid therapy, neutropenia, malnutrition, or prior broad-spectrum antibiotics for more than 7 days in the last month. ICU patients who are not considered at risk for P. aeruginosa infection can be treated initially with an intravenous β-lactam (such as cefotaxime or ceftriaxone) combined with either an intravenous macrolide (azithromycin) or an intravenous fluoroquinolone. Fluoroquinolone monotherapy is not considered appropriate in the setting of severe community-acquired pneumonia. In the ICU patient population considered to be at risk for P. aeruginosa infection, combination antipseudomonal therapy should be used, including intravenous antipseudomonal β-lactams (e.g., cefepime, imipenem, meropenem, piperacillin/tazobactam) plus an intravenous antipseudomonal fluoroquinolone (e.g., ciprofloxacin). Alternatively, an intravenous antipseudomonal β-lactam can be administered along with an aminoglycoside plus either an intravenous macrolide (azithromycin) or an intravenous nonpseudomonal fluoroquinolone.

Treatment for SARS is largely supportive, with oxygen and ventilator therapy as necessary. Specific antiviral therapies for SARS have not yet been well studied, although aerosolized ribavirin has been used empirically.

Most patients respond to empirical antibiotic regimens over the first 3 days of therapy. In general, it is not advisable to alter the antibiotic program in the first 72 hours, unless the patient is deteriorating or culture results indicate alternative therapy. Patients initially begun on parenteral therapy may be changed to an oral regimen when they are afebrile (temperature less than 100° F on two occasions 8 hours apart) and demonstrate improvement in cough, dyspnea, and leukocytosis. For the minority of patients who do not respond to initial empirical coverage, an aggressive search should be undertaken to detect unusual pathogens, alternative diagnoses, such as pulmonary embolism, or complications of pneumonia, such as a complicated pleural effusion, empyema, or lung abscess. Additional diagnostic testing may include computed tomography (CT) of the chest, sampling of pleural fluid, and/or bronchoscopy with collection of respiratory secretions, brushings, and bronchoalveolar lavage for microbiologic analysis. Even when the patient appears to respond to the initial antibiotic regimen, the chest radiograph signs resolve more slowly (over 6 to 8 weeks) than other clinical signs and symptoms. The physician must document that abnormalities on the chest radiograph have resolved completely or, in some cases, led to the formation of a fibrotic scar. Usual practice includes obtaining repeat radiography 6 to 8 weeks after completion of the antibiotic regimen. Persistence of abnormalities on the chest radiograph or the development of recurrent pneumonia in a similar distribution should prompt a careful search for an underlying endobronchial obstruction such as an occult neoplasm, foreign body, bronchostenosis, or broncholithiasis. Follow-up CT scanning is usually the prelude to formal pulmonary consultation for consideration of bronchoscopy and other further diagnostic tests.