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C H A P T E R 2 1 CRITICAL POINTS IN INFECTIOUS DISEASES DON BURKE A 18-year-old male arrives in your emergency room in respiratory distress. He had been complaining of a sore throat for the last two daysf which worsened into a bad headache, an unusual rash and breathing difficulties this evening. Presently, he is combative and confused and you are unable to get vitals due to his agitated state. An important element in the approach to treating patients who are acutely ill from an infection, begins with looking at the host. Having knowledge of the antibiotics is often not as important asunderstanding the person infected. The first aspect to look at, once you have initiated proper oxygen and hemodynamic support, is the immune status ofthe patient.A simple way to break it down is by looking at whether they have a problem with neutrophils, with humoral immunity or with cell-mediated immunity. Each of these scenarios can have different disease patterns and different approaches to treatment. Research has shown that patients treated with the wrong antibiotic (or with no antibiotic) within the first eight hours have a higher mortality.Hence, your first shot has to be reasonably accurate. • Neutrophil Function After leaving the bloodstream, neutrophils migrate predominately to two sites: the subepithelium of the skin and the submucosa of the gut. Hence, patients who have neutropenia or other neutrophil defects are at risk for serious infections with either skin or gut organisms. The absolute neutrophil count (ANC) is determined by adding the percentage of polymorphonuclear leukocytes (PMNs) and bands, then multiplying by the total white blood cell count. An ANC of 15 mg prednisone equivalent per day for > 4 weeks) would make one consider Legionella or Mycobacteria tuberculosis early in the differential. Systemic fungal infections can be divided into thosethatoccurinhealthypersons versus those that are usually only seen in compromised hosts. The former includeblastomycosis, cryptococcosis, histoplasmosis, paracoccidioidomycosis and coccidioidomycosis while the latterinclude aspergillosis, pneumocystosis, candidosis and mucormycosis. Amongst bacterial infections, consider grampositive cocci as potential pathogens when there is a clinical picture typical of pyrogenic exotoxins, with diffuse, blanching erythroderma (like a sunburn), high fever, shock or exfoliation of skin (especially on the extremities). Becauseof the ability of these exotoxins of Staph aureus and group A Strep to intensely stimulate T-cell proliferation (with subsequent production of a variety of immune-activating cytokines), they have been designated superantigens. Treatment options would thereby include therapies that would either inhibit cytokine production (e.g., steroids, activated protein C,high-dose clindamycin) or bind toxin (e.g., immune globulin) in conjunction with conventional antibiotics. Consider gram-negative organisms when you see evidence of purpuric skin lesions or DIG in the presence of shock, suggesting endotoxemia. Ecthyma gangrenosum (purplish-red skin lesions surrounded by near-normal skin with a red rim) should make you think of Pseudomonas aeruginosa until proven otherwise, and antibiotic coverage should include two drugs that cover for this organism (preferably an anti-pseudomonal beta-lactam along with either an aminoglycoside or ciprofloxacin) until culture and sensitivity results comeback. Diabetics, burn patients and patients with lossof colonic mucosal integrity often have polymicrobial infections. Therefore, start with broad coverage and narrow it down if culture results become available. If a patient should present with two separate gramnegative organisms in blood cultures, or Strep mitis or bovis, always think ofsome serious disease in their colon (e.g., cancer, Strongyloides infection). • HelpfulConsiderations Try to avoid central lines unless the drugs being administered are particularly hard on peripheral veins, or the patient has very poor peripheral access. Infectious and other complications with peripheral IVs are generally easier to detect and to rectify than with central venous catheters. Another point to consider is drug fever. A "pearl" is that, with rare exceptions, the presence of eosinophilia usually does not imply a progressive or inadequately treated bacterial infection. In fact, eosinophils are usually suppressed in the presence of bacterial infections. Therefore, consider an adverse drug reaction as a possible culprit. Watch for a pattern to the fever curve (since bacteria never follow patterns), as it may correlate with the timing of a drug. Although deep vein thrombosis and atelectasisare commonly cited as causes of occult fever or elevated WBC counts, these elevations are usually mild and not consistent. If the patient has a continually rising CRITICAL POINTS IN INFECTIOUS DISEASES 229 WBC count or progressive fever, consider more serious etiologies such as abscess (especially is there was a recent surgery), antibiotic resistance(especially...

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