Mastering Infection and Microbiology: A Guide to Diagnosis & Treatment

Infection and Microbiology

1. Musculoskeletal infections overview

2. Treatment overview
3. Empirical treatment: based on the presumed type of infection as determined from clinical findings and symptoms. Staphylococcus and Streptococcus are the most common organisms infecting skin, soft tissue, and bone.
4. Definitive treatment: based on final culture and sensitivity results when available
5. Surgical treatment: draining of contained infections, débridement of dead tissue, restoration of vascularity
6. Bacterial virulence
7. Antibiotic resistance—plasmid
8. β-Lactamase ( bla gene)—makes staphylococci resistant to penicillin
9. Penicillin-binding protein 2a ( mecA gene)—makes
   Staphylococcus aureus MRSA
10. Increased surface adhesion
11. Fnb gene—fibronectin in S. aureus
12. Increases adhesion to titanium

13. Glycocalyx-biofilm-slime-polysaccharide capsule

14. Improves attachment to inert surfaces
15. Protects bacteria from desiccation
16. Cell protection from phagocytosis
17. Toxins
18. Glycocalyx-biofilm-slime-polysaccharide capsule
    —inhibits phagocytosis
19. Hides PAMPs
20. Protects bacteria from toxic enzymes/chemicals
21. Protein A: S. aureus —inhibits phagocytosis
22. Binds immunoglobulins (Fc region of IgG)
23. M protein: group A Streptococcus pyogenes — inhibits phagocytosis
24. Inhibits activation of alternative complement pathway on cell surface
25. Endotoxin: gram-negative lipopolysaccharide capsules
26. Exotoxin
27. Clostridium perfringens: lecithinase— tissue-destroying alpha toxin
28. Myonecrosis and hemolysis of gangrene
29. Clostridium tetani: tetanospasmin— blocks inhibitory nerves
30. “Lockjaw” or muscle spasms
31. Clostridium botulinum : botulism— blocks acetylcholine release
32. “Floppy” baby (also wrinkle relaxers and antispasmodic for cerebral palsy)
33. Community-associated MRSA: Panton-Valentine leukocidin (PVL) cytotoxin
34. Superantigens
35. Pore-forming toxin specific to neutrophils
36. Activate approximately 20% of T cells
37. Trigger cytokine release
38. Systemic inflammation; appears as septic shock
39. S. pyogenes(group A streptococci): M protein
40. S. aureus: TSS toxin-1 causes toxic shock syndrome
41. Acute febrile illness with a generalized scarlatiniform rash
42. Hypotension (shock) with organ system failure
43. Desquamation of palmar/plantar skin lesions (if the patient lives)
44. Treatment:
45. Removal of foreign object (retained sponge or tampon)
46. Supportive care with fluids and anti- Staphylococcus antibiotics
47. Staphylococcus: roughly 80% of orthopaedic infections
48. Antibiotic resistance
49. Penicillin (β-lactam antibiotic)—inhibits peptidoglycan bonds of bacterial cell walls
50. β-Lactamases are enzymes produced by bacteria that provide resistance by breaking down the antibiotic structure.
51. MRSA
52. mecA gene
53. Community versus hospital
54. Located on staphylococcal chromosome cassette mobile element–carrying IV (SCCmecIV)
55. Encodes for penicillin-binding protein 2A, which has a low affinity for β-lactam antibiotics
56. Hospital-acquired MRSA (HA-MRSA) or health care–acquired (HC-MRSA)
57. Seen in patients from nursing homes, those with recent bacteria have larger SCCmec genetic elements
58. Multiple antibiotic
    resistance genes
59. More drug resistance; known as “super bugs”
60. Community-acquired MRSA (CA-MRSA)
61. Bacteria have smaller SCCmec genetic elements

62. Infection by tissue type

63. Less drug resistance
64. Almost all have PVL cytotoxin
65. γ-Hemolysin: a pore-forming toxin that can lyse PMNs
66. Seen in young adults with recurrent boils and severe hemorrhagic pneumonia

67. At-risk groups: athletes, IV drug abusers, homeless persons, military recruits, prisoners

68. Risk factors
69. Previous antibiotic use within 1 year
70. Frequent skin-to-skin contact with others
71. Frequent sharing of personal items
72. Compromised skin integrity

73. Soft tissue infections : superficial to deep ( Table 1.32)

74. Erysipelas: infection of dermis and lymphatics—group A streptococci

75. Painful raised lesion with a red, edematous, indurated (peau d’orange) appearance and an advancing raised border
76. Treatment: penicillins or erythromycin

77. Cellulitis: subcutaneous infection most commonly group A streptococci or S. aureus

78. Acute spreading infection with pain, erythema, and warmth, with or without lymphadenopathy; may develop into abscess (may surround abscess or ulcer)
79. Treatment: routine for cellulitis—penicillin, dicloxacillin; but IV cefazolin or nafcillin if systemic systems prominent or patient is at high risk (asplenia, neutropenia, immunocompromise, cirrhosis, cardiac or renal failure, local trauma, or
    preexisting edema)
    3. Abscess : pus-filled inflammatory subcutaneous nodule (furuncle = “boil”) that may be multiple and may coalesce (carbuncle): almost always S. aureus. Small lesions sometimes mistaken as spider bites.
80. Painful pus under pressure
81. Treatment: incision and drainage (I&D), then left open, with culture and sensitivity testing to select antibiotics.
82. For simple abscesses, addition of systemic antibiotics has not been shown to improve cure rate or decrease recurrence above I&D alone.
83. Systemic antibiotics only for (Infectious Disease Society of America Guidelines):
84. Severe or extensive disease
85. Rapid progression in the presence of associated cellulitis
86. Signs and symptoms of systemic illness
87. Associated comorbidities or immunosuppression, extremes of age
88. Abscess in an area difficult to drain
89. Associated septic phlebitis
90. Lack of response to incision and drainage
91. Empirical antibiotics selected should aim at MRSA.
92. Necrotizing fasciitis
93. Rare, rapidly progressive, life-threatening infection of the fascia and subcutaneous tissue
94. Causes liquefactive necrosis with thrombosis of the cutaneous microcirculation
    3. Most commonly polymicrobial , but group A β-hemolytic (“flesh-eating”) streptococci the most common monomicrobial cause (i.e., S. pyogenes ).
95. Risk factors: diabetes, peripheral vascular disease, liver failure
96. Death most related to delay in treatment for more than 24 hours
97. Fascial infection spreads faster than the observed skin changes.
98. Skin microcirculation thrombosis and later necrosis
99. Early—pain out of proportion, swelling and edema
100. Late
101. Blisters/bullae
102. Skin that does not blanch (skin is dying)
103. Skin becomes numb (nerves are dying)
104. Difficult diagnosis—paucity of cutaneous findings so high clinical suspicion needed
105. Less than one-fifth of cases diagnosed at admission; preadmission antibiotics mask severity
106. Repeated examinations noting margins that migrate quickly despite antibiotic treatment
107. Surgical findings
108. Grayish necrotic fascia
109. Lack of normal muscular fascial resistance to blunt dissection
110. Lack of bleeding of the fascia during dissection
111. Foul-smelling “dishwater ” pus
112. Treatment: broad-spectrum antibiotics
113. Early operative débridement of all necrotic tissue—level selected should be ahead of the infection
114. Amputation/disarticulation should be considered.
115. Second-look procedure should be performed 24 hours later for reevaluation.
116. Gas gangrene
117. C. perfringens(obligate anaerobe) most common organism that produces gas and toxins in subcutaneous tissues and muscle
118. Dirty wound managed with primary closure: war wounds, tornado, lawn mower
119. Inadequate débridement of more severe devitalizing injuries
120. Clostridial dermonecrotizing exotoxin lecithinase
121. Crepitance of soft tissue, air in soft tissues on x-rays, foul “sweet”-smelling discharge
122. Treatment
123. Early, adequate, and thorough surgical débridement
124. Delayed closure and second-look procedure 24 hours later for reevaluation
125. High-dose IV penicillin and hyperbaric oxygen can help if available.
126. Surgical site infection
127. Infections are the product of bacteria that take hold in a favorable wound environment in a host with a susceptible immune system.
128. Bacterial issues
129. Load
130. Prevention

131. More than 10 5 colony-forming units (CFUs) needed in normal host to cause infection

132. Need only about 100 CFUs if foreign object present
133. Prophylactic antibiotics
134. Given from less than 1 hour before until 24 hours after procedure
135. Repeated if preceding time is more than 4 hours (longer than half-life of antibiotic selected)
136. Repeated if blood loss more than 1000 mL
137. Doubled if patient weighs more than 80 kg (>176 lb)
138. Avoidance of hematogenous seeding
139. No active infections in elective cases
     —legs, feet, toes checked preoperatively
140. Table 1.32 Soft Tissue Infections Type Affected Tissues Clinical Findings Cellulitis, erysipelas Superficial, subcutaneous
     Erythema; tendern warmth; lymphangitis;
     Aggressive, life threatening may be associated an underlyi vascular dis (particularl diabetes)
     Commonly occ after surger trauma, or streptococc skin infecti
     Progressive, se pain; edem (distant fro the wound) foul-smellin serosanguin discharge; h fever; chills tachycardia confusion
     Clinical finding consistent toxemia
     Radiographs typically sh widespread in the soft tissues (facilitates r spread of th infection) Staphylococcal Toxemia, not septicemia
     In orthopaedics, TSS is secondary to colonization of surgical or
     Fever, hypoten an erythemato macular ras with a sero exudate (gr positive coc Tox shock syndrome: Muscle; commonly in grossly contaminated, traumatic wounds, particularly those that are closed primarily Gas gangrene Muscle fascia Necrotizing fasciitis lymphadenopa
     traumatic wounds (even after minor trauma)
     TSS can be
     associated with tampon use through colonization of the vagina with toxin-producing S. aureus
     Similar to
     staphylococcal Marine injuries Varies History of fishi (or other m activity) inj with signs o infection
     Culture specim at 30°C (60
     organisms take several weeks to gr on culture media
     Varies Surgical wound infection Toxemia, not septicemia
     Commonly
     associated with erysipelas or necrotizing fasciitis Streptococcal
     are present)
     The infected wound ma look benign which may the seriousn of the underlying condition
141. If urologic symptoms: urinalysis and culture
142. Postpone surgery if:
143. Over 103 CFUs and dysuria/frequency
144. Symptoms of urinary obstruction
145. Reduced force, hesitancy, straining
146. Foley catheterization should be discontinued as soon as possible after surgery.
147. MRSA: carrier screening and eradication, “active detection and isolation (ADI)”
148. Nasal carriage—important risk factor, with some controversy; if patient part of high-risk population
149. Screening
150. Swab culture versus PCR
151. If positive screen result: postoperative infection rates are two to nine times higher
152. Use
     vancomycin 1 g every 12 hours
153. 2% intranasal mupirocin ointment twice daily × 5 days
154. 2%
     chlorhexidine showers daily × 5 days
155. Nutrition (malnutrition associated with wound dehiscence and infection)
156. Clinical evaluation
157. History of weight loss (10% over 6 months or
     5% over 1 month)

158. Albumin value less than

159. 3.5 g/dL, total lymphocyte count less than 1500 cells/µL, transferrin level less than 200 mg/dL
160. Obesity—body mass index (BMI)
     more than 30 kg/m2; higher numbers
     = more wound problems
161. Bariatric consultation should be considered early in course for patient likely to progress to need large elective procedure.
162. Smoking: two to four times more infections/osteomyelitis
163. Hypoxia—CO binds to Hb = carboxyhemoglobin (HbCO)
164. Nicotine—microvascular vasoconstriction
165. Reduced bone, skin, soft tissue healing
166. Cessation of smoking 4 to 6 weeks preoperatively leads to decreased complications.

167. Alcohol: heavy alcohol use (blood alcohol >200 mg/dL) increases rate of infections 2.6 times

168. Reduced fibroblast production of collagen type I
169. Inhibits osteoblasts: reduced osteocalcin, inhibits Wnt/β-catenin pathway
170. Diabetes
171. Special soft tissue infections
172. Impairs fracture healing
173. Associated with “bad behaviors,” cirrhosis, and liver failure
174. Chronic issues well known: cardiac, renal, peripheral vascular, neuropathy
175. Best measured with HbA1c—goal is less than 6.9% of total hemoglobin
176. Acute hyperglycemia is also a threat
177. Collagen synthesis suppressed at blood glucose value of 200 mg/dL—impaired wound healing
178. WBC phagocytosis impaired at blood glucose value of 250 mg/dL—decreased ability to fight infection
179. Bite infections ( Table 1.33)
180. Initial treatment: exploration of wound, removal of foreign objects, débridement, and irrigation
181. Consider delayed primary closure at 48–72 hours
182. Antibiotic prophylaxis controversial
183. Should be considered for bites to hands, feet, face
184. Wounds hard to clean—deep punctures, edema/crush injury
185. Bites involving tendon, cartilage, or bone
186. Bites in immunocompromised or asplenic host
187. Bite prophylaxis antibiotics: amoxicillin-clavulanate
188. For penicillin-allergic patient, trimethoprim-sulfamethoxazole plus clindamycin
189. Antibiotic treatment: oral unless infection rapidly spreads or patient is febrile or high risk; then IV
190. Bite organisms
191. Most oral flora is polymicrobial in nature. Some bacteria are more specific to source of “bite.”
192. Human bites: Streptococcus viridans common,
     Eikenella corrodens
193. “Fight bite” x-rays for cartilage divots, broken teeth, and formal identification
194. Cat bites: Pasteurella multocida
195. 50% require surgery—puncture wounds to tendons/joints
196. Dog bites: P. multocida, Pasteurella canis
197. Marine injuries
198. Mycobacterium marinum
199. Slow culture at low temperature (30°C)
200. Noncaseating granulomas
201. Treatment: 3 months of minocycline or clarithromycin
202. Erysipelothrix rhusiopathiae
203. Erysipeloid—fish handler ’s (also swine handler ’s) disease
204. Gram-positive bacillus
205. Painful, itchy, spreading, purple ring-shaped lesion
206. Treatment: oral penicillin
207. Vibrio vulnificus
208. Oyster bite
209. Bullae and necrotizing fasciitis from gram-negative motile rod
210. Gastroenteritis from eating bad oyster
211. Treatment: I&D and broad-spectrum antibiotics (ceftazidime)
212. Tick bite (Ixodes): Lyme disease
213. Borrelia burgdorferi(a spirochete)
214. Erythema migrans: bull’s-eye lesion
215. Vector: white-footed deer mouse in northeast and Pacific north
216. Knee effusions
217. Neurologic disease: Bell palsy common

218. Treatment: amoxicillin versus doxycycline

219. Rabies (neurotropic virus)
220. Raccoon/skunk/bat bites
221. CNS irritation, “hydrophobia,” paralysis, and death
222. Death if not treated before symptoms occur

223. Treatment: human rabies immune globulin

224. Septic bursitis
225. Similar pathology whether in olecranon, prepatellar, or pretibial bursa
226. Redness, swelling, pain, and subcutaneous fluctuance
227. About 80% caused by S. aureus, others streptococci
228. Chronic recurrent cases can be fungal or mycobacterial
229. Aspiration with Gram stain and culture if redness is presence
230. Treatment
231. Tetanus
232. Serial aspirations and oral antibiotics
233. IV antibiotics for systemic symptoms and in immunocompromised patients
234. Bursectomy for persistent or recurrent cases
235. Potentially lethal neuroparalytic disease leading to trismus (lockjaw)
236. Exotoxin from anaerobe C. tetani
237. Tetanospasmin blocks inhibitory nerves.
238. Deep wounds and devitalized tissues are at high risk.
239. Wounds more than 6 hours old, more than 1 cm deep, ischemic, crush, grade III
240. Contaminated with soil or feces, animal bite
241. Vaccination
242. Tetanus toxoid (Td) 0.5-mL diphtheria-tetanus toxoid booster every 10 years
243. Adults with at-risk wounds, give Td booster
244. Status unknown or history of fewer than three doses: give both Td and tetanus immune globulin (TIG)