Pneumonia Features ================== þ Atypical Pneumonias - Legionella has abrupt onset, patchy nonsegmental and unilateral infiltrates and frequent diarrhea. The patient typically has bradycardia on presentation Abstract: Postgraduate Medicine 1991 Oct;90(5):89-90,95-98,101 Cunha BA 921253 In addition to typical community-acquired pneumonias caused by pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus, there are some atypical organisms that may cause pneumonia. These include Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella species, and less commonly Chlamydia psittaci (psittacosis), and Coxiella burnetii (Q fever). Diagnosis of pneumonia is complicated by the fact that occasionally pathogens appear in combinations. In contrast to typical pneumonias, atypical types are either unresponsive to conventional antibiotics (penicillins, cephalosporins) or show different clinical symptoms, especially extrapulmonary features not present in typical pneumonias, including headache, pleuritic pain, mental confusion, and diarrhea. The three most common atypical pneumonias today are Mycoplasma pneumonia, legionnaires' disease (Legionella), and TWAR (Chlamydia pneumoniae). Mycoplasma pneumonia occurs slightly more often in winter than at other times of the year and affects mainly 10- to 30-year-old patients. It has an incubation period of 2 to 3 weeks and frequently produces headaches, fever, and nonproductive coughs. Legionnaires' disease predominates in persons over 60 years of age, occurs more frequently in late summer or early fall and shows an increased incidence rate in smokers and patients with liver disease. Two key signs of legionnaires' disease are relative bradycardia and hypophosphatemia. TWAR presents similar to Mycoplasma infection but differs by the absence of diarrhea and the presence of laryngitis. A variety of antibiotics are used in the treatment of pneumonia but none of them is effective against all typical and atypical pathogens. Tetracyclines and erythromycin are often used in Mycoplasma infections and legionnaires' disease, but Chlamydia pneumoniae (TWAR) responds only to doxycycline or minocycline. In cases that respond equally well to several drugs, the more cost- effective drug is usually chosen. þ Chlamydia pneumonia - (per Scientific American Medicine): - 10% of all pneumonia is U.S. is from Chlamydia - Transmission by aerosol route possible, but spread is slow in a closed population, with 31-day interval between cases. - Pneumonia and bronchitis most common syndromes caused by Chlamydia pneumoniae; others include pharyngitis, sinusitis, otitis, sometimes combined with pneumonia. - Onset subacute and symptoms nonspecific (sore throat, low-grade fever). - Hoarseness more common with Chlamydia than other pneumonias. - May be associated with coronary atherosclerosis (higher titers in those with atherosclerosis). - TAR: Chlamydia pneumonia is seasonal, in younger people. þ Staphylococcal pneumonia - uncommon - it comprises just 1% of bacterial pneumonias. - It is seen most commonly after a viral infection, but is also seen in intravenous drug abusers, hospitalized patients and debilitated patients. - It often causes an empyema and early abscess formation - more likely to be complicated by a pneumothorax than the other common bacterial pathogens. - Reference: Tintinalli 3rd ed. p 264, 266 þ Klebsiella and Pneumococcal Pneumonia - Both type 3 pneumococcus and Klebsiella pneumoniae cause currant jelly sputum and a lobar infiltrate. Either can cause a bulging minor fissure (more commonly seen with Klebsiella infection). How does the usual location of the infiltrate differ between these organisms? Klebsiella usually causes an upper lobe infiltrate, whereas a pneumococcal pneumonia is more likely to infect a lower or middle lobe. Ref: Tintinalli 3rd ed. p 265