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E case #20-B Eric Liu, M.D. October 29-November 2, 2001 Patient is a 65 y.o. male who presents with a copious cough for several days. He complains of fevers to 100.6, and occasional chills and sweats. He has no sinus congestion or sore throat. He does have dyspnea with walking to the kitchen, but not at rest. His sputum is primarily green, with minimal hemoptysis. He is not a smoker. His PMH includes an ischemic cardiomyopathy and diet controlled diabetes. His exam demonstrates LLL rales, but no wheezing. His cardiac exam demonstrates moderate MR, no gallops. His CXR shows a dense alveolar infiltrate in his left lower lobe. His room air saturation is 92%.
DISCUSSION The most common organism is Streptococcus pneumoniae. It accounts for two-thirds of all cases. It is a gram-positive cocci. The most challenging aspect recently is the emergence of resistant strains. Twenty four percent are moderatley resistant to penicillin (MIC 0.1 - 1.0 ug/ml), and ten percent are highly resistant (MIC > 2.0 ug/ml). Therefore, it is not possible to uniformly treat with penicillin without testing for drug susceptibility. The treatment of choice more moderate resistance is intravenous penicillin or oral amoxicillin. Highly resistant strains are treated with vancomycin or a floroquinolone. It is also important to note that nonsusceptible strains are resistant to macrolides and oral cephalosporins. Initial therapy is still emperic with the need for coverage while awaiting susceptibility testing. Haemophilus influenzae is a gram-negative rod. It is a common organism in community-acquired pneumonia, and often seen in COPD. Moraxella catarrahlis is the third organism that is seen in CAP that is uncomplicated. It is a gram-negative diplococci. Initial treatment regimens recommend a macrolide antibiotic such as azithromycin or clarithromycin to cover these organisms. Alternatives include doxycycline that has similar coverage and is markedly less expensive. Fluoriquinones are are also acceptable choices as broad spectrum/first line agents in most protocols. (Consideration should be made to reserve these agents for other indications, secondary to cost and the need to limit development of drug resistence.) The atypical organisms are a part of the differential diagnosis. Mycoplasma pneumoniae is usually seen in young/healthy adults. It is typified by an incubation period of two to four weeks, and then a prodromal phase of fever, chills, headache and sore throat. Later, a cough develops that is primarily dry or scant in mucous. Other symptoms are cold agglutinatins, hemolytic anemia, myocarditis, rash and neurological syndromes. Diagnosis is made by the use of rising IGM and IGG titers - which are delayed, and therefore of limited clinical use. Treatment is emperical, with a macrolide or doxycycline (or fluroquinilone). Chlaymadia pneumoniae accounts for 5 - 15% of pneumonias. It characteristically has a prodromal phase also, and has low mortality. It is however, often seen in association with other organisms such as Streptococcus pneumoniae. Diagnosis is made serologically, and treatment is emperical. Legionella is the third most common atypical organism. It is seen in two to six percent of pneumonia nationally, though it is regional. The most common areas are in the Northeast and Great Lakes, and it is extremely rare in the Northwest. It carries higher mortality, and can be seen with high fever, hyponatremia, and CNS manifestations. Diagnosis is made with a urine DFA assay which is seventy percent sensitive, and confirmed by culture. The preferred therapy is erythromycin with or without rifampin. Some protocols recommend azithromycin instead (with or without rifampin), or a fluroquinolone. Co-morbid conditions that cause a degree of immunocompromise extend the differential diagnosis to include the coliforms. The principal organisms in this group are Escherichia coli and Klebsiella pneumoniae. These organisms are usually nosocomial bacteria, and belong to a group of other nosocomial gram negatives including Proteus, Serratia, enterobacter, Pseudomonnas and acinetobacter. The latter two tend to cause pneumonia in the debilitated, mechanically ventilated or patients that have received previous antibiotics. Therapy in community acquired pneumonia cases include a second or third generation cephalosporin or amoxicillin/clavulanate (with or without a macrolide), or a fluoroquinolone alone. Aspiration pneumonia is seen in patients with compromised consciousness or dysphagia. People at risk have poor dentition, which harbors anaerobic organisms. The principal organisms are prevotella melaninogenica, peptostreptococcus, fusobacterium nucleatu, and bacteriodes. There are three distinct clinical syndromes - ranging from a chemical pneumonitis from acids, obstruction from a foreign body, to clinical infection. Dependant lobes are affected: in an upright patient that is the lower lobes, and in supine patients, the superior segment of the lower lobes, and the posterior segment of the upper lobes are involved. In addition, most lung abscess cases are caused by anaerobic organisms. These patients may have a putrid discharge, necrosis of tissue, or bronchopulmonary fistula. Clindaycin is superior to penicillin in clinical trials. Metronidazole has higher failure rates - from the role of aerobic and microaerophilic streptococci. Pneumocystis carinnii pneumonia is seen exlusively in patients with defective cell-mediated immunity. It is important to note that one-fifth of patients are unaware of the HIV status at the time of admission, and PCP is the most common initial AIDS defining diagnosis. Also, all bacterial organisms are more frequent early in the course of HIV, and frequent sinusitis or bronchitis can be early signs of immunocompromise. PCP presents with a nonproductive cough, fever and dyspnea. Radiographs are usually interstitial. Sputum samples are sixty percent sensitive, with bronchoscope yields over 95%. Influenza is an important infection of adults. The majority who die are the elderly, and usually from bacterial superinfection from Streptococcus pneumonia, and rarely from Staph. aureus. Treatment with amantadine or rimantidine may reduce symtoms, but it is unclear what are the effects on mortality or superinfection. Other points
These are balanced by high false positive rates with normal flora, as well as high false negative rates with normal flora overgrowing causative organism. The American Thoracic Society recommends against routine sputum cultures, while the Infectious Diseases Society of America supports its use in toxic/hospitalized patients.
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