General Surgery (Board Review Series) 1st Edition

4

Surgical Infections

Traves D. Crabtree

1. Perioperative Wound Infections
2. Operative cases

• are classified by the level of bacterial contamination (Table 4-1).

1. Clean operative cases

• are associated with a wound infection rate of less than 3%.

2. Clean-contaminated cases

• are associated with a wound infection rate of 3% to 10%.

3. Contaminated cases

• are associated with a wound infection rate of 5% to 15%.

4. Dirty cases

• are associated with a wound infection rate as high as 10% to 40% if wounds are closed primarily. These wounds should be left open and allowed to heal by secondary intention.

1. Perioperative antibiotic prophylaxis

• has been shown to decrease the postoperative wound infectionrate in clean-contaminated procedures.

1. Other indications for prophylaxis
2. Some clean cases (e.g., elective inguinal hernia repairs, breast surgery) may also benefit from antibiotic prophylaxis.
3. Antibiotic prophylaxis is generally accepted with procedures that involve insertion of prosthetic material or foreign bodies; clean operations in patients with impaired host defenses; and neurosurgical, cardiac, and ophthalmologic procedures.
4. Other considerations are the patient's overall health statusand the length of operation.

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2. Prophylactic antibiotics

• should be administered within 1 hourbefore incision. If given more than 24 hours postoperatively, antibiotics have not been shown to provide additional benefit in decreasing infection rates.

1. A preoperative bowel preparation

• with nonabsorbable antibiotics and cathartic agents [e.g., polyethylene glycol (GoLYTELY)], in conjunction with antibiotics, may decrease the postoperative wound infection rate in surgery of the lower alimentary tract.

1. Antibiotic prophylaxis

• plays a small role in preventing wound infections relative to the role of adequate surgical débridementand meticulous attention to proper surgical technique.

3. Contaminated and dirty wounds

• generally require a course of antibiotic therapy after appropriate débridement and drainage have been performed.

Table 4-1. Classification of Operative Cases Based on Potential Bacterial Contamination

Wound Classification Viscus Injury Spillage Break in Surgical Technique Trauma Finding of Infection or Inflammation Example Clean None None None None No inflammation Elective inguinal hernia Clean-contaminated Controlled/planned viscus entry Minimal Minimal None Emergent clean case, reopen clean case Elective bowel resection Contaminated Unintended viscus entry Gross GI spillage Major Injury < 4 hours old Presence of infected urine or bile Colon injury during cholecystectomy Dirty Perforated viscus encountered Fecal contamination present – Injury > 4 hours old, foreign body, devitalized tissue Purulent material encountered Traumatic colon injury GI = gastrointestinal.

1. The American Heart Association has provided recommendations for perioperative antibiotic prophylaxis in patients at risk for bacterial endocarditis.
2. Antibiotic prophylaxis is recommended in patients with

• prosthetic cardiac valves.
• rheumatic valvular dysfunction.
• most congenital cardiac malformations.
• mitral valve prolapse with regurgitation.
• previous history of bacterial endocarditis.

2. Antibiotic prophylaxis is not required in patients with

• previous coronary artery bypass grafting.
• isolated secundum atrial septal defect.
• physiologic/functional heart murmurs.

3. Prophylaxis for endocarditis in at-risk patients

• is generally recommended in procedures with a significant risk for transient bacteremia(e.g., abdominal surgery, most urologic procedures, many dental procedures).

4. For general surgical procedures

• a regimen of ampicillinand gentamicin is recommended perioperatively.
• Patients with penicillin allergies may receive vancomycin and gentamicin.

1. Prophylaxis against tetanus for traumatic injuries depends on the characteristics of the injury and the patient's immunization status.
2. Characteristics of tetanus-prone woundsinclude

• wounds over 6 hours old.

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• injuries more than 1-cm deep.
• irregular skin borders.
• the presence of devitalized tissue or obvious contamination.
• crush, burn, frostbite, and missile injuries.

2. Tetanus immune globulin

• is administered only in tetanus-prone wounds in unimmunized patients or if the immunization status is unknown.

3. Tetanus toxoid

• is administered depending on the patient's immunization status as outlined in Table 4-2.

Table 4-2. Schedule for Administration of Tetanus Toxoid in Traumatic Injuries

Wound Class Unknown or < 3 Doses Tetanus Immunization History ≥ 3 Doses ≥ 3 Doses and > 5 Years Since Booster ≥ 3 Doses and > 10 Years Since Booster Tetanus-prone Yes No (yes if wound > 24 hours old) Yes Yes Nontetanus-prone Yes No No Yes Adapted from MMWR 1990;39:37–41.

1. Skin and Soft Tissue Infections
2. Primary infections of the skin (pyodermas)

• include impetigo, erysipelas, cellulitis, and folliculitis.

1. Most of these infections are caused by Staphylococcusand Streptococcus species.
2. Antibiotics alone are often sufficient treatment because the vascular supply to the area of infection remains intact.
3. Specific environments may predispose to primary skin infections with uncommon organisms; for example, Pseudomonasspecies can cause “hot-tub folliculitis.”
4. Abscesses

• are infections that contain a nonvascular central portioncomprised of necrotic debris from leukocytes, bacteria, and tissue components.

1. Treatment
2. Drainageof an abscess is the definitive treatment, with antibiotics serving as adjunctive therapy.
3. Antibiotics aloneare insufficient treatment because of the poor vascular supply to an abscess.
4. The organisms within abscesses

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• may include one predominant bacteria or multiple bacteria, both aerobic and anaerobic, depending on the original source of bacteria.

1. Soft tissue abscesses above the waist are often associated with Staphylococcusor Streptococcus species.
2. Perirectal and intra-abdominal abscessesoften contain mixed aerobic and anaerobic pathogens originating from fecal or intestinal flora.
3. Bite wounds

• may become infected 15% to 20% of the time.

1. Organisms in human bite wounds

• include Staphylococcusspecies, oral anaerobes, Eikenella species, and Haemophilus influenza.

1. Eikenellaspecies cause permanent joint injury.
2. Closed-fist injuries should be carefully examined for joint involvement.
3. These closed-fisted wounds should not be closedand should be débrided appropriately.
4. Appropriate antibiotics and tetanus prophylaxisshould also be instituted.
5. Organisms in animal bites

• may include streptococci, staphylococci, anaerobes, and Pasteurella multocida(more common in cat bites).

1. Necrotizing soft tissue infections
2. Organisms producing gangrene or necrosis of soft tissue

• most often include Streptococcusspecies and then Clostridium species. Other organisms often cultured from such infections include Bacteroides, Enterobacter, andEnterococcus.

2. Classic “gas gangrene”

• is myonecrosis produced by clostridium species, and less frequently by staphylococcusand streptococcus species.

1. Clostridiumand streptococcus species

• may produce a rapid fulminant coursewith severe toxemia occurring within 24 hours of wound inoculation.

1. Characteristic findingsinclude

• severe pain.
• dishwater-like” nonpurulent discharge.
• early toxemia.
• wound edema and crepitus.
• nonerythematous skin with bullous lesions.
• late skin necrosis.

1. Treatment

• The primarytherapy is early aggressive surgical débridement.
• Penicillin G provides adequate coverage for these clostridiumand streptococcus species.

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• Additional coverage for potential mixed infections may be appropriate (e.g., aminoglycoside).
• Adjunctive hyperbaric oxygen therapy may also be of some benefit.

3. Fournier's gangrene

• refers to necrotizing soft tissue infections of the perineal/scrotal region.

1. Bacteriaoften originate from a primary colonic or genitourinary source.
2. Etiologiesinclude rectal trauma, perirectal abscesses, pilonidal cysts, posthemorrhoidectomy infections, and various primary and secondary urologic infections.
3. Diabetes is a significant risk factorfor development of these infections.
4. Infections are polymicrobial and require aggressive débridementof the perineum and scrotum with sparing of the testes.
5. Toxic shock syndrome (TSS)

• is most frequently caused by staphylococcusspecies, although streptococcus species may also produce this syndrome.

1. Staphylococcal TSS

• often originates from infections involving mucous membranesas well as soft tissue infections.
• may result from colonization of wounds without overt infection.

2. Streptococcal TSS

• often originates from invasive skin and soft tissue infections.

3. Characteristicsinclude

• rapid onset of fever.
• refractory hypotension.
• diffuse erythematous desquamating rash.
• vomiting and diarrhea.
• conjunctival injection.
• strawberry tongue.
• multisystem organ failure.

4. Treatment

• involves aggressive fluid resuscitationused in conjunction with antibiotics and surgical débridement when appropriate.

1. Intravenous (IV) administration of immune globulin against toxic shock syndrome toxin (TSST)may improve patient outcome.
2. Antistaphylococcal penicillins (e.g., nafcillin) are appropriate for staphylococcal-induced TSS.
3. Penicillin Gin conjunction with clindamycin is appropriate antibiotic coverage for streptococcal-induced TSS.

• Clindamycin inhibits protein synthesis and thus may inhibit TSST production.

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III. Nosocomial Infections (Table 4-3)

1. Nosocomial pneumonia

• has a mortality rate of 20% to 50%.

1. Risk factors
2. The most important risk factor for the development of nosocomial pneumonia is mechanical ventilation.
3. Endotracheal tubes and tracheostomy tubes do not prevent aspiration of oropharyngeal contents even with a cuff inflated.
4. H₂-blocking agents alter gastric pH and allow for bacterial colonization of the stomach, which may increase the risk for pneumonia.
5. Differential diagnosisin the critically ill patient includes

• adult respiratory distress syndrome.
• congestive heart failure.
• pulmonary hemorrhage or contusion.
• pulmonary embolus.
• pleural effusion.
• atelectasis.

3. Diagnostic featuresinclude

• isolation of a predominant organism from sputum or lavage specimens without significant contamination from oral flora.
• characteristic radiographic findings.
• fever.
• productive purulent sputum.
• respiratory compromise.

4. Common pathogens

• include Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella, Enterobacter, Escherichia coli, Serratia, and Proteus.

5. Treatment

• involves appropriate antibiotic therapyin conjunction with aggressive management of pulmonary secretions.

1. Urinary tract infections

• are the most common nosocomial infections.

1. The greatest risk factor

• is placement of urinary catheters.

2. Common pathogens

• include E. coli, Pseudomonas, Klebsiella, Staphylococcus epidermidis, and Candida albicans.

3. Treatment

• involves antibiotic therapywith meticulous care of indwelling catheters and prompt removal when appropriate.

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Table 4-3. Postoperative Nosocomial Infections

Nosocomial Infection Risk Factors Signs and Symptoms Common Pathogens Diagnosis Treatment Pneumonia Tracheal intubation Purulent sputum, respiratory compromise Pseudomonas, Staphylococcus, Klebsiella, Escherichia coli, Serratia, Proteus CXR, positive cultures, clinical suspicion Antibiotics, management of pulmonary secretions Urinary system infection Urinary tract catheterization/instrumentation Urinary frequency, dysuria E. coli, Pseudomonas, Klebsiella, Staphylococcus, Epidermidis, Candida albicans Pyuria, positive cultures Antibiotics, prompt removal and meticulous care of indwelling catheters IV catheter-related infections TPN, Multilumen>single lumen, femoral>>subclavian or jugular Recurrent fever, persistent bacteremia Staphylococcus species, gram-negative rods, Enterococcus, Candida Positive blood cultures, positive catheter tip cultures Removal of catheter, antibiotics Sinusitis Facial fractures,nasoenteric/nasotracheal tubes Purulent nasal secretions, facial pain Polymicrobial, gram-negative organisms Air fluid levels radiographically, positive cultures of sinuses Removal of foreign bodies, antibiotics Pseudomembranous colitis Recent antibiotic therapy Diarrhea, abdominal pain Clostridium difficile Cytotoxin in stool specimen, colonoscopy,C. difficile in stool cultures Oral or IV metronidazole(Flagyl), oral vancomycin CXR = chest radiograph; IV = intravenous; TPN = total parenteral nutrition.

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1. Intravenous catheter-related infections

• are most often caused by staphylococcusspecies although gram-negative bacteria and Candida may also be a source.

1. Relative risk factorsinclude

• administration of total parenteral nutrition (TPN).
• multilumen catheters (more than single-lumen catheters).
• femoral catheters (more than subclavian or jugular catheters).

2. Treatment

• involves prompt removal of the catheter with adjunctive antibiotics.

1. Other potential nosocomial infections in the critically ill patient
2. Pseudomembranous colitis

• is caused by an exotoxinproduced by Clostridium difficile.
• characteristically presents after a course of antibiotic therapysecondary to alterations in normal colonic flora.
• can be initiated by any antibioticand can present several weeks after completion of antibiotic therapy.

1. Signs and symptoms

• may include watery diarrhea, abdominal pain, and fever.

1. Diagnosis
2. The diagnosis is confirmed by demonstrating the presence of cytotoxin in stool samples.
3. Colonoscopy may also be diagnostic by directly visualizing the characteristic pseudomembranes on the colonic mucosa.
4. When suspicious of pseudomembranous colitis

• prompt diagnosisis essential for treatment.

1. Adequate treatmentincludes IV or oral metronidazole therapy and cessation of inciting antibiotics, if possible.
2. Oral vancomycin may be used if there is a contraindication to metronidazole therapy or for failure of initial treatment.
3. Surgeryis rarely necessary unless complications such as perforation or toxic megacolon arise.
4. Sinusitis

• accounts for 5% of intensive care unit–acquired infections (see BRS Surgical Specialties, Chapter 4 III B).

3. Other infectious and inflammatory processesthat should be considered in the critically ill postoperative patient include

• deep vein thrombosis.
• thrombophlebitis.
• parotitis.
• perirectal abscess.
• cholecystitis, appendicitis, or other intra-abdominal source.
• pancreatitis.

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4. Fungal infection

• should be suspected if there are persistent signs or symptoms of infectionin a critically ill patient despite broad spectrum antibacterial therapy.

1. Hepatitis B, C, and Human Immunodeficiency Virus (HIV) Exposure in Surgery
2. Hepatitis B virus (HBV)
3. The risk of transmission

• to nonimmunized individuals after a needlestick with a contaminated needleis 30% overall.
• is 2% if the infected patient is negative for hepatitis B e antigen (HB_eAg)and is as high as 40% if the infected patient is HB_eAg-positive.
• is increased with increasing size of the inocula of blood with hollow needles (e.g., IV catheters), which pose a greater risk than suture needles.

1. Although rare, transmission with bite wounds and inoculation of mucosal membranes with contaminated blood has been documented.
2. Bodily fluids, such as semen, vaginal fluid, and saliva, are also considered potential sources of HBV infection, although their role in occupational transmission is not yet defined.
3. Immunization for HBVis now recommended for newborn children and individuals at high risk for exposure to HBV, including

• health-care and public safety workers.
• hemodialysis patients.
• hemophiliacs.
• homosexual males.
• IV drug abusers.
• household and sexual contacts of HBV carriers.

3. Administration of the HBV vaccine

• to previously vaccinated individualsafter exposure depends on the level of serum anti-HB_sAg, as outlined in Table 4-4.

4. Prophylaxis

• in unvaccinated individualsexposed to HBV (e.g., needlestick) should include hepatitis B immune globulin (HBIG) and the HBV vaccine given at two different sites. HBIG is considered efficacious if administered within 7 days of exposure.

1. Hepatitis C virus (HCV)
2. The risk of transmission of HCV

• in a nonimmunized individual after percutaneous injury from an infected individualis 3% to 10%.

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• is low relative to the risk of HBV.

1. Transmission from contaminated bloodor blood products is the primary modality of infection.
2. Blood contamination of mucosal membranes, semen, and vaginal fluid are other plausible sources that have not been reliably confirmed.
3. Currently there are no recommendations for immunizationagainst HCV or for postexposure prophylactic therapy, although exposed patients should receive serial serum tests for anti-HCV antibodies after exposure to document seroconversion.

Table 4-4. Prophylaxis for Hepatitis B After Exposure to Hepatitis B–Positive Source

Exposed Person Exposure Source HBsAg+ HBsAg- Unvaccinated HBIG + HB vaccine HB vaccine Vaccinated Anti-HBs ≥ 10 mIU/mL* No treatment No treatment Anti-HBs < 10 mIU/mL HBIG + 1 dose HB vaccine No treatment Adapted from MMWR 1991; 40(RR–13):1–25. Anti-HBs = serum antibody to hepatitis B surface antigen; HB = hepatitis B; HBIG = hepatitis B immune globulin; HBsAg = serum hepatitis B surface antigen. *Exposed individuals should be tested for serum anti-HBs antibody titers.

1. Human immunodeficiency virus (HIV)
2. The risk of transmission of HIV

• after percutaneous injury from an infected individualis 0.2% to 0.5%.
• The estimated HIV transmission rate per operation from an HIV-positive patient to the surgeon is 1/130,000.

2. Chemoprophylaxis
3. with an antiretroviral regimen, including zidovudine (AZT) and lamivudine (3TC) ± a protease inhibitor [i.e., indinavir (IDV)], decreases the rate of seroconversionafter occupational exposure to HIV.
4. This ideally should be administered within 1 to 2 hoursafter exposure, although prophylaxis may be considered up to 2 weeks later in high-risk exposures.
5. Recommendation of postexposure chemoprophylaxis depends on the exposure risk and the associated morbidity of the antiretroviral regimen.
6. Regimens are often individualized based on the source's antiretroviral therapy and the potential for HIV-resistant strains.
7. after a percutaneous injuryis recommended if exposure involves a large volume of HIV-positive blood (i.e., deep large-bore IV injury) or exposure to blood with a high titer of HIV [i.e., end-stage acquired immunodeficiency syndrome (AIDS)].
8. should be offered when bloodor various bodily fluids [e.g., semen; vaginal secretions; cerebrospinal fluid (CSF); synovial, pleural, peritoneal,

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pericardial, and amniotic fluids] are introduced percutaneously or when contact with mucous membranes occurs.

1. should be offered with skin exposureto these bodily fluids when exposure involves a high titer of HIV, prolonged contact, an extensive area of exposure, or an area with visibly compromised skin integrity.
2. should not be offered when the exposure does not increase the risk of HIV seroconversion.

• For example, there have been no definitively confirmed cases of seroconversion after a solid suture needle injury from an asymptomatic HIV-positive patient.
• This includes exposure to urine, saliva, or feces.

3. Testing of exposed individuals for HIV antibodies

• should be performed at 6 weeks, 12 weeks, and 6 months, with seroconversion typically occurring within 6 to 12 weeks.

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Review Test

Directions: Each of the numbered items or incomplete statements in this section is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case.

Questions 1–4

A 62-year-old man underwent an elective left hemicolectomy with primary anastomosis for Stage II colon adenocarcinoma. Twenty-four hours postoperatively, his temperature was 38.8°C (102°F), his heart rate (HR) was 100 beats/min, and his blood pressure (BP) was 150/90 mm Hg. Breath sounds were diminished in both lung bases, while the rest of the physical examination was unremarkable. Chest radiograph revealed bibasilar atelectasis. Seven days postoperatively, his temperature increased to 39°C (102.2°F), his HR increased to 130 beats/min, and his BP was 90/60 mm Hg. His lungs were clear on physical examination and there was no evidence of wound infection. The patient complained of increasing abdominal bloating and worsening abdominal pain.

1. In regard to this patient's immediate postoperative fever, which of the following is an appropriate statement?

(A) The patient's fever was due to a wound infection

(B) Prophylactic perioperative antibiotics have been shown to prevent the development of nosocomial pneumonia in the postoperative patient

(C) Improved pain control may have indirectly helped to decrease the patient's temperature

(D) All peripheral intravenous catheters should have been immediately removed because of their risk of infection

(E) Pulmonary atelectasis causes fever by bacterial stimulation of inflammatory mediators

1–C. Fever occurring in the first 48 hours postoperatively without any obvious source of infection after careful evaluation may arise from a pulmonary source of inflammatory mediator stimulation associated with atelectasis. This process is not felt to be bacterial or infectious in nature and can frequently be alleviated by measures that improve the patient's ability to ventilate collapsed alveoli such as incentive spirometry or improved pain control, which may allow for improved respiratory effort. Prophylactic perioperative antibiotics do not decrease the rate of postoperative pneumonia, though they decrease the wound infection rate in selected cases. Although rare, wound infections can occur within the first 24 to 48 hours postoperatively with aggressive strains of Streptococcus or Clostridium. Inspection of all intravenous (IV) sites is essential in evaluating the postoperative patient with fever; however, immediate removal of all peripheral IV catheters is not warranted.

2. Which of the following statements is true regarding the use of perioperative prophylactic antibiotics in this patient?

(A) Prophylactic antibiotics should be administered 24 hours before surgery to decrease the rate of wound infection

(B) If no spillage of fecal material occurred, antibiotics are not indicated because it is a clean case

(C) Shaving the evening before surgery decreases the wound infection rate compared with shaving immediately before incision

(D) A preoperative bowel preparation with nonabsorbable antibiotics alone decreases the rate of postoperative infectious complications

(E) The most important intra-operative factor in preventing postoperative wound infections is appropriate dosing of prophylactic antibiotics

2–D. For elective surgery on the colon, a preoperative bowel preparation with nonabsorbable antibiotics and cathartic agents decreases the rate of postoperative infectious complications, although prophylactic intravenous (IV) antibiotics may also provide some additional benefit. There is no decrease in infection rates if prophylactic perioperative antibiotics are administered 24 hours preoperatively versus within 1 hour of surgery. In addition, shaving the skin at the incision site the evening before surgery provides no benefit in decreasing wound infection rates and may actually increase the wound infection rate secondary to the induction of microabscess formation. The most important factors in decreasing the postoperative wound infection rate are attention to proper surgical technique and adequate surgical débridement when appropriate. An uncomplicated elective colon resection involves controlled entry into the gastrointestinal tract and is considered a clean-contaminated case.

3. Which of the following is an appropriate consideration in the diagnosis and treatment of this patient?

(A) This patient probably has an early nosocomial pneumonia

(B) A decrease in this patient's temperature when incentive spirometry is initiated would prove that atelectasis is the source of fever

(C) Antibiotics should be started for treatment of a potential urinary tract infection

(D) An abdominal computed tomography (CT) scan is appropriate to rule out a potential intra-abdominal source of infection

(E) Antifungal therapy should be initiated immediately

3–D. Although there are many potential sources of nosocomial infection in the postoperative patient, an intra-abdominal source should always be considered after abdominal surgery. An abdominal computed tomography (CT) scan would be a valuable diagnostic examination in this patient to assess the abdomen for potential sources of infection. Although thorough evaluation for other potential sources of infection is necessary, there is no evidence provided suggesting that the patient has clinically relevant pneumonia, nor is there any evidence of a urinary tract infection at this point. Routine administration of antifungal agents without any evidence of a fungal infection is not indicated.

4. For wound infections presenting in the early postoperative period (< 48 hours), which of the following statements is true?

(A) Clostridium and streptococcus species are frequent pathogens

(B) The bacterial contamination leading to wound infection typically occurs in the postoperative period

(C) The rate of wound healing is unaffected by wound infections occurring in the early postoperative period

(D) Débridement of an infected wound should be performed if antibiotic therapy fails

(E) They are generally caused by slow-growing, nonvirulent bacteria

4–A. Although rare, wound infections occurring within the first 48 hours postoperatively in an otherwise uncomplicated case frequently are caused by fast-growing, virulent strains ofclostridium or streptococcus species. Bacterial introduction into the wound that results in postoperative infection most often occurs intraoperatively rather than postoperatively. Treatment involves adequately débriding devitalized or necrotic tissue and providing adequate drainage of an infected wound, with antibiotics serving as adjuncts in the therapy. Wound infections are a leading cause of wound healing failure. Risk factors for the development of wound infections include the presence of foreign bodies, poor approximation of wound edges, tissue ischemia (i.e., inadequate fluid resuscitation or sutures too tight), and the presence of devitalized tissue, hematomas, or seromas.

5. A 22-year-old man underwent percutaneous pin fixation of a right ankle fracture as an outpatient. Three days later he presents at the emergency department complaining of vomiting and mild shortness of breath, but denies any pain. The wound is without obvious drainage or erythema. His temperature is 39°C (102.2°F), his heart rate is 140 beats/min, and his blood pressure is 90/40 mm Hg. His chest radiograph is clear and his creatinine is 3.4. Which of the following statements is true regarding this patient?

(A) The causative organism is most likely a clostridial species

(B) An intra-abdominal source of infection is likely

(C) Outpatient antibiotic therapy is indicated

(D) Renal failure is secondary to associated bacteremia

(E) A desquamating erythematous rash is characteristic

5–E. Toxic shock syndrome (TSS) is most often caused by virulent strains of Staphylococcus or Streptococcus and may frequently produce a rapid fulminant course. A diffuse desquamating erythematous rash, frequently away from the site of injury, is characteristic of TSS and may provide a clue to the diagnosis. The pathogenesis of TSS is related to a toxin called toxic shock syndrome toxin (TSST) produced locally by these bacteria and not necessarily by bacteremia. Although possible, a concomitant intra-abdominal source of infection is unlikely given this scenario. Outpatient management would be inappropriate given his condition and potential for continued rapid deterioration.

6. After a routine right inguinal hernia repair, a 42-year-old man develops erythema over the incision. A wound infection is diagnosed and the patient is discharged to home on 10 days of ciprofloxacin. Three weeks later he returns with complaints of persistent watery diarrhea with a low-grade fever. His temperature is 38.3°C (101°F), his heart rate is 80 beats/min, and his blood pressure is 125/65 mm Hg. Which of the following is the most appropriate next step in the management of this patient?

(A) Intravenous (IV) vancomycin therapy

(B) Colonoscopy

(C) No treatment, because the cause is probably viral

(D) Oral clindamycin

6–B. Following a course of antibiotics, one should always be suspicious of the diagnosis of pseudomembranous colitis in a patient with the history given. Although this process could be viral, appropriate diagnostic measures should be taken to rule out pseudomembranous colitis. It is generally appropriate to try to confirm the presence of Clostridium difficilecytotoxin in stool specimens, although identifying plaque-like pseudomembranous lesion by colonoscopy would be highly suggestive of such a diagnosis; but this is not routine. Treatment is with oral or intravenous (IV) metronidazole, or nonabsorbable oral vancomycin, although metronidazole is the preferred treatment given the cost considerations and the potential risk of developing vancomycin-resistant Enterococcus strains.

Questions 7–8

A 24-year-old migrant farm worker presents to the emergency department with complaints of pain at the site of a 4-cm laceration on his right leg. The patient states that he was cut by the end of a shovel while working 2 days earlier, but did not seek medical attention at that time because he was able to stop the bleeding. The patient does not recall ever having been immunized for tetanus.

7. Which of the following is the most important initial step in the management of this patient?

(A) Admission to the hospital and administration of intravenous (IV) broad spectrum antibiotics with close observation of the wound

(B) Administration of tetanus toxoid

(C) Oral antibiotics and scheduling of close follow-up as an outpatient

(D) Wound inspection, irrigation, and débridement

(E) Careful closure of the laceration with administration of broad spectrum IV antibiotics

7–D. Although intravenous (IV) antibiotics and appropriate tetanus immunization should be administered early in the course of treatment, initial attention should be devoted to inspection, irrigation, and adequate débridement of the injured site. In a dirty wound with exposure to soil contaminants such as this one, closure of the laceration is inappropriate given the high risk of infection. The decision to manage such a patient as an outpatient should be individually based after adequate assessment of the patient and the wound.

8. Which of the following would be the most appropriate regimen with regard to prophylaxis for tetanus?

(A) Administration of tetanus booster

(B) Administration of a full dose of tetanus toxoid

(C) Administration of tetanus toxoid in the dominant arm and tetanus immune globulin in the nondominant arm

(D) Administration of tetanus toxoid and tetanus immune globulin in the nondominant arm

(E) Administration of tetanus toxoid and tetanus immune globulin in the gluteal region

8–C. In an unimmunized patient with a tetanusprone wound, a full regimen of both tetanus toxoid and tetanus immune globulin should be administered. When administering the toxoid (antigen) in conjunction with immune globulin (antibody to the antigen) injections should be performed at separate sites to avoid any potential interaction between the antigen and antibody, which could potentially interfere with both the passive and active immunization.

Directions: Each group of items in this section consists of lettered options followed by a set of numbered items. For each item, select the appropriate lettered option(s) most closely associated with it. Each lettered option may be selected once, more than once, or not at all.

Questions 9–12

Match each scenario with the correct causative organism.

1. Staphylococcus aureus
2. Clostridium tetani
3. Clostridium difficile
4. Candida albicans
5. Bacteroides fragilis
6. Escherichia coli
7. Pseudomonas aeruginosa
8. Klebsiella pneumoniae
9. Proteus mirabilis
10. Haemophilus influenzae
11. A 48-year-old man has been in the intensive care unit for 5 weeks after a severe motor vehicle accident with multiple injuries. He has been on broad spectrum antibiotics for 3½ weeks. He now has persistent fever with associated worsening refractory hypotension. There is no obvious source of infection on physical examination, by abdominal computed tomography (CT), or on chest radiograph. The only new finding is the presence of new retinal lesions on funduscopic examination. (SELECT 1 ORGANISM)

9–D. Definitive diagnostic criteria for disseminated candidal sepsis include endophthalmitis, positive tissue cultures for Candida, burn wound invasion, and positive peritoneal cultures in the setting of peritonitis. The presence of Candida in blood cultures and in cultures of multiple other sites (three or more sites) is also highly suggestive of the development of candidal sepsis in the critically ill patient. Disseminated candidiasis can often produce a rapid fulminant course with an associated high mortality rate (> 50%). Such infection should be considered in the critically ill patient receiving long-term broad spectrum antibiotics.

10. A 68-year-old, alcoholic man has been in the hospital for 36 hours after a motor vehicle accident with multiple orthopedic injuries. He develops a fever with painful swelling of his right cheek. There is purulent material noted at the opening of Stensen's duct. There is no other obvious source of infection on physical examination or chest radiograph. (SELECT 1 ORGANISM)

10–A. Although parotitis is an uncommon cause of postoperative fever, it should be considered in the differential diagnosis. Dehydration, as may be seen in alcoholic patients, is a risk factor for the development of parotitis with partial obstruction of the parotid duct contributing to the infectious or inflammatory process. The most common organism found in such infections is Staphylococcus aureus. Parotitis typically presents with fever, a swollen painful cheek, and purulent exudate from the opening of the parotid duct (Stensen's duct).

11. A 48-year-old woman has been in the intensive care unit for 3 weeks after repair of a grade III liver laceration and colonic perforation sustained from a motor vehicle accident. She has been ventilator-dependent since admission and has received 2 weeks of broad spectrum antibiotics for a presumed intra-abdominal source of infection. She now has persistent fever with a worsening infiltrate on chest radiograph. Computed tomography (CT) scan reveals no obvious intra-abdominal source of infection and the rest of the physical examination is normal. Sputum cultures reveal gram-negative rods. (SELECT 2 ORGANISMS)

11–A, G. Nosocomial pneumonia is a common complication seen in critically ill, hospitalized patients, particularly in patients who require prolonged ventilatory assistance. Diagnostic criteria include productive purulent sputum, radiographic evidence of an infiltrate, positive cultures of sputum or lavage specimens without significant oral contamination, respiratory compromise, and fever. Although many organisms may be identified as the inciting agent, overall, the two most common organisms identified in nosocomial pneumonia arePseudomonas aeruginosa (gram-negative rod) and Staphylococcus aureus (gram-positive cocci).

12. A 52-year-old man has been in the intensive care unit for 4 weeks after a surgical débridement for necrotizing pancreatitis. He remains ventilator-dependent and has been on intravenous (IV) antibiotics for aspiration pneumonia. The patient now has a persistent fever without any obvious source of infection on physical examination. His chest radiograph reveals resolution of a right lower lobe infiltrate and CT scan of the abdomen reveals no obvious source of infection. Proctoscopic examination reveals plaque-like lesions on the mucosa of the distal sigmoid colon. (SELECT 1 ORGANISM)

12–C. The diagnosis of pseudomembranous colitis should always be considered as a potential source of infection in any patient receiving long-term antibiotic therapy. Symptomatology may be more subtle in the critically ill patient. Although not routine, the identification of characteristic pseudomembranous lesions on endoscopic examination of the rectosigmoid provides adequate diagnostic criteria for this disease. Confirmation of Clostridium difficile cytotoxin in stool specimens may also confirm the diagnosis.