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HIV infection
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Obligate intracellular retrovirus
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Primarily affects lymphocyte and macrophage cell lines
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Decreases helper cells (CD4 + cells)
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Approximately 50,000 new cases/year reported by the CDC
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Increased in: homosexual men, patients with hemophilia, and IV drug abusers
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One-fifth of those infected know they are HIV positive.
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AIDS
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Diagnosis requires an positive HIV test result plus one of the following:
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Transmission rate
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One of the opportunistic infections (e.g., pneumocystis)
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CD4+ cell count of less than 200 cell/ µL (normal, 700–1200 cells/µL)
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Increases with amount of blood exposed and viral load
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Decreases with postexposure antiviral prophylaxis
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From a contaminated needlestick: 0.3%
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From mucous membrane exposure: 0.09%
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From a blood transfusion: approximately 1 per 500,000 per unit transfused
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From frozen bone allograft: less than 1 per 1 million
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Donor screening—most important factor in preventing viral transmission
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No cases from fresh frozen bone allograft have been reported since 2001.
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Most sensitive screen—nucleic acid amplification testing (NAAT)
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HIV positivity is not a contraindication to performing required surgical procedures.
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HIV-positive patients more likely to have THA
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Higher association with liver disease, drug abuse, coagulopathy
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Development of acute renal failure and postoperative infection more likely
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Asymptomatic HIV-positive individuals have no significant difference in short-term infection risks.
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Orthopaedic manifestations more common in later stages
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Increased infections:
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Polymyositis: viral muscle infection
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Pyomyositis: S. aureus
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TB
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Bacillary angiomatosis (Bartonella henselae) from cats
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Reactive arthritis (Reiter syndrome)
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Non-Hodgkin lymphoma and Kaposi sarcoma
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Osteonecrosis
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Mechanism of Action of Antibiotics
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Class of Examples Mechanism of Action Antibiotic |
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β-Lactam antibiotics |
Penicillin, cephalosporins |
Inhibit cross-linking of polysaccharides in the cell wall by blocking transpeptidase enzyme |
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Aminoglycosides |
Gentamicin, tobramycin |
Inhibit protein synthesis (the mechanism is through binding to cytoplasmic 30S-ribosomal subunit) |
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Clindamycin and macrolides |
Clindamycin, erythromycin, clarithromycin, azithromycin |
Inhibit the dissociation of peptidyl-transfer RNA from ribosomes during translocation (the mechanism is through binding to 50S-ribosomal subunit) |
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Tetracyclines |
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Inhibit protein synthesis (binds to 50S-ribosomal subunit) |
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Glycopeptides |
Vancomycin, teicoplanin |
Interfere with the insertion of glycan subunits into the cell wall |
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Rifampin |
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Inhibits RNA polymerase F |
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Quinolones |
Ciprofloxacin, levofloxacin ofloxacin |
Inhibit DNA gyrase |
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Oxazolidinones |
Linezolid |
Inhibit protein synthesis (binds to 50S-ribosomal subunits) |
Table 1.36
Antibiotic Indications and Side Effects
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Antibiotics Sensitive Complications/Other Information Organisms |
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Aminoglycosides |
G−, PM |
Auditory (most common) and vestibular damage is caused by destruction of the cochlear and vestibular sensory cells from drug accumulation in the perilymph and endolymph Renal toxicity Neuromuscular blockade |
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Amphotericin |
Fungi |
Nephrotoxic |
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Aztreonam |
G− |
Ineffective against anaerobes |
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Carbenicillin/ticarcillin/piperacillin |
Better against G− than G+ |
Platelet dysfunction, increased bleeding times |
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Cephalosporins: |
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Nausea, vomiting, diarrhea |
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Prophylaxis (surgical) |
Cefazolin is the drug of choice |
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First generation |
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Second generation |
Some G+, some G− |
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Third generation |
G−, fewer G+ |
Hemolytic anemia (bleeding diathesis [moxalactam]) |
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Chloramphenicol |
Haemophilus influenzae, anaerobes |
Bone marrow aplasia |
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Ciprofloxacin |
G−, MRSA |
Tendon ruptures; cartilage erosion in children; antacids reduce absorption of ciprofloxacin; theophylline increases serum concentrations of ciprofloxacin |
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Clindamycin |
G+, anaerobes |
Pseudomembranous enterocolitis |
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Daptomycin |
G+, MRSA |
Muscle toxicity |
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Erythromycin |
G+ |
In cases of PCN allergy Ototoxic |
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Imipenem |
G+, some G− |
Resistance, seizure |
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Methicillin/oxacillin/nafcillin |
Penicillinase resistant |
Same as penicillin; nephritis (methicillin); subcutaneous skin slough (nafcillin) |
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Penicillin |
Streptococcal, G+ |
Hypersensitivity/resistance; hemolytic |
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Polymyxin/nystatin |
GU |
Nephrotoxic |
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Sulfonamides |
GU |
Hemolytic anemia |
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Tetracycline |
G+ |
In cases of PCN allergy Stains teeth/bone (contraindicated up to age 8 yr) |
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Vancomycin |
MRSA, Clostridium difficile |
Ototoxic; erythema with rapid IV delivery |
G − , Gram-negative; G+, gram-positive; GU, genitourinary; PCN, penicillin; PM, polymicrobial.
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Hepatitis
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Hepatitis B (HB)
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Blood transmission: bite/sexual/occupational
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Singlestick transmission rate in the unvaccinated: approximately 30%
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Causes cirrhosis, liver failure, and hepatocellular carcinoma
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Screening and vaccination have reduced the risk of transmission for health care workers.
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