Common organisms causing Atypical Pneumonia

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Elsevier ClinicalKey Clinical Overview

Terminology Mycoplasma pneumoniae is a common bacterial pathogen causing respiratory tract infections in both children and adults Mycoplasma pneumoniae commonly causes mild, prolonged symptoms of upper respiratory tract infection or acute bronchitis Asymptomatic carriage is common in children and may play a role in transmission Tracheobronchitis is the most common illness among children infected with Mycoplasma pneumoniae Pneumonia due to Mycoplasma pneumoniae most often occurs in older children and adults; it is the most common form of atypical pneumonia Terminology of typical and atypical pneumonias reflects a historical distinction from decades ago; it remains in use despite being broad rather than precise Atypical pneumonias are characterized by different antibiotic response and a different pattern of clinical features than typical bacterial pneumonias caused by pneumococcus Does not respond to β-lactam antibiotics (eg, penicillin) or sulfonamides Tends to feature dry cough, patchy lung involvement, and overlap with upper respiratory tract infection symptoms Rarely, nonrespiratory manifestations may accompany respiratory disease or occur without obvious respiratory disease Nonrespiratory manifestations include mucocutaneous disease, hemolytic anemia, central nervous system manifestations (eg, meningoencephalitis, transverse myelitis), and carditis

Diagnosis Clinical presentation of Mycoplasma pneumoniae respiratory tract disease is similar to that seen with other "atypical" bacterial pathogens, including Chlamydia pneumoniae ( Chlamydophila pneumoniae ) and Legionella species, in addition to various respiratory viral pathogens; it also overlaps in features with respiratory tract disease from "typical" bacterial pathogens (eg, pneumococcus) Pneumococcal pneumonia Disease caused by pneumococcus ( Streptococcus pneumoniae ) Most common bacterial cause of community-acquired pneumonia (incidence varies worldwide and may vary by changing rates of pneumococcal vaccination and smoking) Symptoms similar to those of Mycoplasma pneumoniae infection include fever, cough, and pharyngitis Patients with invasive pneumococcal disease are typically more ill appearing, and laboratory findings may demonstrate a leukocytosis with left shift Clinical course and response to empiric treatment most often serve to differentiate the 2 infections Unlike Mycoplasma pneumoniae infection, cough may be productive of purulent or blood-tinged sputum, pleuritic chest pain is common, and both physical examination and chest radiograph suggest dense consolidation Unlike Mycoplasma pneumoniae disease, Streptococcus pneumoniae infections respond well to sulfonamides or β-lactam antibiotics Chlamydia pneumoniae ( Chlamydophila pneumoniae ) infection Causes atypical pneumonia (less commonly than Mycoplasma pneumoniae ) Responsible for approximately 10% of community-acquired pneumonia in adults; the proportion is likely less in children As with Mycoplasma pneumoniae , Chlamydia pneumoniae infection can cause bronchitis, cough, and malaise Gradual onset; incubation period is approximately 21 days Infection may persist for weeks or months Unlike in Mycoplasma pneumoniae infection, laryngitis is a common manifestation

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Elsevier ClinicalKey Clinical Overview

Synopsis Chlamydia pneumoniae infection causes a wide spectrum of clinical manifestations that range from asymptomatic carrier state to acute upper airway disease (eg, pharyngitis, laryngitis, sinusitis) and lower airway disease (eg, community-acquired pneumonia, bronchitis), mainly in adults and older children Acute symptomatic infection presents with laryngitis, pharyngitis, rhinorrhea, headache, cough, and low-grade fever; atypical pneumonia may develop and is characterized by worsening cough, dyspnea, and sometimes sputum production Physical examination findings are nonspecific (eg, wheezing, rales, rhonchi); chest radiograph findings are variable and nonspecific (eg, interstitial infiltrates, multilobar infiltrates, pleural effusions) It is nearly impossible to distinguish Chlamydia pneumoniae from other common causes of community-acquired pneumonia (eg, viruses, Legionella , Mycoplasma ) on clinical grounds alone; however, among patients with atypical bacterial pneumonia, presence of laryngitis suggests Chlamydia pneumoniae as the cause Coinfection with other bacterial pathogens (eg, Streptococcus pneumoniae , Mycoplasma pneumoniae ) and viral pathogens (eg, respiratory syncytial virus, influenza virus) is common Presumptive diagnosis is based on clinical presentation and chest radiograph findings consistent with pneumonia; isolation and identification of Chlamydia pneumoniae is problematic and uncommonly done Mild to moderate disease in patients without significant comorbidity is often self-limiting and does not require specific treatment; infection with severe manifestations (eg pneumonia) may require antimicrobial therapy

Diagnosis Table Title: Comparison of the features of Chlamydia psittaci , Chlamydia pneumoniae , Mycoplasma pneumoniae, and Legionella pneumophila infections. Table Caption: –, rare; +, occurs in some cases; ++, occurs in many cases; +++, occurs frequently; *Disparity between chest radiograph changes and relatively minor dyspnea. **Clear improvement after 48 hours but may not be totally afebrile. Table Citation: From Stewardson AJ et al: Psittacosis. The atypical pneumonias. Infect Dis Clin North Am. 24(1):7-25, 2010, Table 3. Table Heads: Clinical feature| Chlamydia psittaci| Chlamydia pneumoniae| Mycoplasma pneumoniae| Legionella pneumophila Table Rows: Cough| ++| +| ++| + Sputum| -| +| ++| +++ Dyspnea| +| +| ++| +++ Sore throat| -| ++| -| - Headache| +++| +| -| + Confusion| +| -| -| ++ Diarrhea| -| -| -| + Chest radiograph changes| Minimal| Minimal| Disparity*| Often multifocal Hyponatremia| -| -| -| ++ Leukopenia| -| -| -| + Abnormal liver function tests| +| -| +| ++ Response to doxycycline| Rapid--afebrile within 48 hours| Prompt**| Prompt**| Improved but still unwell