Chapter 138. Moraxella Infections (Part 2) Other Syndromes Local extension causing empyema is very uncommon, and—as might be inferred from the low rate of bacteremia—metastatic complications of M. catarrhalis pneumonia, such as septic arthritis, are exceedingly rare. As of 1995, 58 cases of bacteremic infection due to M. catarrhalis had been reported, mainly in children <10 years old or adults >60 years old; most of these patients had severe underlying lung disease and/or were immunocompromised. The syndromes reported have included bacteremia with no apparent focus, pneumonia, endocarditis, and meningitis. A petechial or purpuric rash, reminiscent of that observed in meningococcal sepsis and associated with disseminated intravascular coagulation, has been described in a few cases. Diagnosis Microscopic examination of Gram-stained sputum yields characteristic findings (Fig. 138-1). The presence of many polymorphonuclear leukocytes without epithelial cells indicates that the sputum sample is of good quality; since most patients with Moraxella infection have chronic lung disease, it is usually not difficult to obtain an acceptable specimen. Large numbers of Moraxella organisms are seen as gram-negative cocci, often lining up side by side and thus resembling pairs of kidneys. Moraxella Infections: Treatment M. catarrhalis is widely susceptible to most antibiotics used to treat lower respiratory tract infection (Table 138-1). Penicillin resistance first appeared in isolated strains in the mid-1970s and is now found in 94% of clinical isolates. This resistance is mediated by two closely related β-lactamases, BRO-1 and BRO-2. These enzymes are active against penicillin, ampicillin, and amoxicillin but less so against cephalosporins, especially third-generation cephalosporins; they also bind avidly to clavulanic acid and sulbactam. Thus a β-lactam/β-lactamase inhibitor combination such as amoxicillin/clavulanate offers excellent treatment. Second- and third-generation cephalosporins are effective alternatives. Isolates in the United States are also nearly uniformly susceptible to fluoroquinolones, newer macrolides, ketolides, and doxycycline; ~90% are susceptible to trimethoprim- sulfamethoxazole. A 5-day course of therapy has been shown to cure respiratory infection, although a longer course is required in sinusitis. Table 138-1 Therapy for Infection Caused by Moraxella Catarrhalis Drug(s) Dose and Duration Oral Therapy for Lower Respiratory Infection a Trimethoprim-sulfamethoxazole 160/800 mg qd for 5–7 days Doxycycline 200 mg/d for 5–7 days Azithromycin 500 mg/d for 5 days Telithromycin 800 mg/d for 5–7 days Amoxicillin/clavulanic acid 500 mg tid for 7 days Ciprofloxacin 500 mg bid for 5 days Cefuroxime 250–500 mg bid for 10 days Cefpodoxime 200 mg bid for 10–14 days Parenteral Therapy for Lower Respiratory Infection in Hospitalized Patients b Ampicillin/sulbactam 1.5/0.5 g q6h Ceftriaxone 1 g/d Cefotaxime 1 g q8h Azithromycin 500 mg/d a The same dosages apply for sinusitis, but some authorities treat f or 10 days with macrolides, tetracyclines, and quinolones and for 14 days with β- lactam agents. b After the patient's condition has stabilized, the regimen may be changed to oral medications at the indicated doses and durations. Treatment of sinusitis or otitis media is empirical, as appropriate specimens are usually obtained only in research studies. In the treatment of pneumonia during the period between the identification of gram-negative cocci in a Gram-stained specimen and the final identification of the organisms by culture, the severity of the condition and the potential presence of other infecting organisms should guide antibiotic selection. For example, an exacerbation of bronchitis caused by M. catarrhalis might be treated with doxycycline or an advanced macrolide. However, the microscopic identification of this organism in a patient with pneumonia may still lead to a preference for initial therapy (at least until culture results become available) with ampicillin/sulbactam, a third-generation cephalosporin, or a quinolone because of the possibility that resistant pneumococci are also present but have been overlooked by Gram's stain. . Chapter 138. Moraxella Infections (Part 2) Other Syndromes Local extension causing empyema is very uncommon, and—as. acceptable specimen. Large numbers of Moraxella organisms are seen as gram-negative cocci, often lining up side by side and thus resembling pairs of kidneys. Moraxella Infections: Treatment M. catarrhalis. findings (Fig. 138- 1). The presence of many polymorphonuclear leukocytes without epithelial cells indicates that the sputum sample is of good quality; since most patients with Moraxella infection