The following cases and commentary, which involve treating and preventing wounds, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 15).
Case 1: Infection after transplant
A 63-year-old woman is evaluated for fever and hypotension 4 days after kidney-pancreas transplantation surgery. She was treated with cyclosporine, prednisolone, and mycophenolate mofetil. The incisional pain has not increased, and, except for slightly increased erythema surrounding the incision, there are no localizing signs or symptoms. Medical history is significant for type 1 diabetes mellitus since the age of 12 years. Until the onset of her current symptoms, she had been doing well after surgery.
On physical examination, temperature is 39.4°C (102.9°F), blood pressure is 88/52 mm Hg, pulse rate is 100/min, and respiration rate is 20/min. Cardiopulmonary examination is normal. On abdominal examination, there is erythema surrounding the surgical right lower quadrant incision and moderate tenderness to palpation of the surgical wound. The remainder of the examination is normal.
Laboratory studies show hemoglobin, 12.1 g/dL (121 g/L); leukocyte count, 13,400/µL (13.4 × 109/L); creatinine, 1.9 mg/dL (168 µmol/L); urinalysis, 7 leukocytes/hpf, 25 erythrocytes/hpf, and trace protein.
The patient and organ donor are serologically positive for cytomegalovirus infection.
A chest radiograph reveals no infiltrates. Abdominal radiographs show only a small amount of free peritoneal gas. CT scans of the chest and abdomen reveal only some peri-incisional fluid.
Which of the following is the most likely cause of this patient's current symptoms and findings?
A. Candidal wound infection
B. Cytomegalovirus infection
C. Pneumocystis jirovecii pneumonia
D. Staphylococcal wound infection
Case 2: Diabetic foot infection
A 56-year-old woman with diabetes mellitus is evaluated in the emergency department for fever, chills, and hyperglycemia. She is up-to-date on all immunizations. Current medications include insulin glargine and insulin aspart and aspirin.
On physical examination, temperature is 39.0°C (102.3°F), blood pressure is 90/60 mm Hg, pulse rate is 104/min, and respiration rate is 21/min; BMI is 28. There is fissuring in the web spaces between many of the toes of both feet. A 4- × 3-cm necrotic ulcerative lesion extending from the first and second toe to the plantar aspect of foot, with significant warmth and extensive surrounding erythema, is noted. Dorsalis pedis pulses are decreased bilaterally. Sensation over the distal lower extremities is decreased.
Laboratory studies show hemoglobin, 13.0 g/dL (130 g/L); leukocyte count, 25,000/µL (25 × 109/L); platelet count, 175,000/µL (175 × 109/L); erythrocyte sedimentation rate, 100 mm/h; plasma glucose, 440 mg/dL (24.4 mmol/L); and creatinine, 1.8 mg/dL (159.1 µmol/L) (1.2 mg/dL [106.0 µmol/L] 3 months ago).
The rest of the comprehensive metabolic panel, including serum aminotransferase concentrations, is normal. An MRI of the foot is ordered.
Which of the following is the best empiric antibiotic treatment option?
C. Vancomycin plus imipenem
D. Vancomycin plus metronidazole
Case 3: Mammoplasty wound
A 42-year-old woman is evaluated for a postoperative wound infection. Eight weeks ago, the patient underwent bilateral augmentation mammoplasty. Six weeks after surgery, she developed violaceous draining nodules at the surgical closure site of the right breast. After 7 days of dicloxacillin, the wound had enlarged. Wound cultures grew normal skin flora. The patient was hospitalized, and intravenous vancomycin plus cefepime was added but without clinical benefit. A second set of wound cultures grew a few colonies of Candida albicans. Medical history is otherwise unremarkable.
On physical examination, temperature is 38.0°C (100.4°F), blood pressure is 105/75 mm Hg, pulse rate is 84/min, and respiration rate is 16/min. Her left breast surgical scar is well healed, and the right breast surgical wound is partially opened and packed along the medial half. The lateral half of the wound is erythematous, with two sinus tracts draining purulent material.
Which of the following is the most likely causative agent for her wound infection?
A. Fluconazole-resistant Candida albicans
B. Methicillin-resistant Staphylococcus aureus
C. Mycobacterium abscessus
D. Mycobacterium tuberculosis
E. Nocardia asteroides
Case 4: Preventing pressure ulcers
A 75-year-old man is admitted to a nursing home after having a stroke 2 weeks ago. The patient has residual right-sided paralysis, aphasia and urinary incontinence. He can respond to verbal commands but cannot speak well enough to make his needs known. His ability to walk is greatly impaired, and he spends most of the day in bed or in a chair. He is unable to change position independently and needs assistance with all activities of daily living. The patient has a poor appetite, cannot use his right arm to feed himself, and is eating only half his meals. He also has intermittent urinary incontinence.
Which of the following is the most appropriate intervention for preventing pressure ulcers in this patient?
A. An air-fluidized bed
B. A doughnut cushion when seated
C. A foam mattress overlay
D. Bladder catheterization
E. Massage of skin over pressure points
Case 5: Dog bites woman
A 39-year-old woman is evaluated in the emergency department for fever, myalgia, and malaise 2 days after her pet dog bit her on the left lower extremity. Medical history is significant for a splenectomy 5 years ago following a motor vehicle accident. She has received tetanus, pneumococcal, meningococcal, and Haemophilus influenzae type B vaccines, and her dog's immunizations are up-to-date. There are no allergies, and the remainder of the medical history is noncontributory.
On physical examination, temperature is 38.7°C (101.7°F), blood pressure is 90/60 mm Hg, pulse rate is 110/min, and respiration rate is 26/min; BMI is 26. There is erythema and tenderness at site of the puncture wound on the left thigh. An abdominal laparotomy scar is noted. There is no inguinal lymphadenopathy. The remainder of the physical examination is normal.
Laboratory studies show hemoglobin, 10.0 g/dL (100 g/L); leukocyte count, 16,600/µL (16.6 × 109/L) with 56% neutrophils, 33% band forms, 10% lymphocytes, and 1% monocytes; platelet count, 17,500/µL (17.5 × 109/L); peripheral blood smear, many Howell-Jolly bodies; blood urea nitrogen, 40 mg/dL (14.3 mmol/L); creatinine, 2.4 mg/dL (212.2 µmol/L); alanine aminotransferase, 500 U/L; and aspartate aminotransferase, 450 U/L.
Multiple blood cultures reveal growth of gram-negative rods/bacilli. The urinalysis is normal. Radiographs of the left femur show no gas or foreign body.
Which of the following is the most likely cause of this patient's septic presentation?
A. Capnocytophaga canimorsus
B. Escherichia coli
C. Salmonella species
D. Staphylococcus aureus
E. Streptococcus pyogenes
Answers and commentary
Correct answer: D. Staphylococcal wound infection.
This patient's symptoms are most likely attributable to a postoperative wound infection considering the recent surgery, rapid onset of high fever, leukocytosis, wound erythema and tenderness, presence of peri-incisional fluid, and lack of signs and symptoms supporting other likely problems in the immediate postoperative period. In patients receiving solid organ transplants, infections in the immediate postoperative period are similar to those occurring in patients who have undergone other types of surgery. Posttransplantation wound infections from staphylococci (coagulase-negative and Staphylococcus aureus), hemolytic streptococci, or enteric bacteria occur commonly.
Candidal wound infection would be less likely than staphylococcal wound infection in this patient because of the acuity of onset, leukocytosis, and high fever. Candidal wound infections are very uncommon and would be expected to be more chronic in nature.
Cytomegalovirus (CMV) infection is unlikely because it would rarely become clinically apparent this soon after surgery and with such a short duration of immunosuppressive therapy. Because the donor and recipient are both serologically positive for CMV, CMV infection might well occur between the second and sixth month after surgery unless prophylaxis is given.
Pneumocystis jirovecii pneumonia is unlikely to be responsible for this patient's current signs and symptoms because it is not likely to occur this soon after transplantation, and this patient demonstrates no respiratory signs and symptoms and has a normal pulmonary examination and chest radiograph.
- Infections in the immediate posttransplantation period are usually the same as those occurring after other kinds of surgery and include staphylococci (coagulase-negative and Staphylococcus aureus), hemolytic streptococci, or enteric bacterial wound infection.
Correct answer: C. Vancomycin plus imipenem.
This patient has a severe limb- and life-threatening diabetic foot infection as evidenced by her systemic symptoms, hypotension, tachycardia, and multiple metabolic derangements; she requires treatment with vancomycin plus imipenem. The lower-extremity findings of decreased foot pulses indicate peripheral arterial disease, and the decreased sensation reflects a sensory neuropathy. In addition, the fissures between the toes are a likely portal of entry for infection. The size of the wound and the increased erythrocyte sedimentation rate suggest potential bone infection.
These severe infections are polymicrobial and can include anaerobes, aerobic gram-positive cocci, and aerobic gram-negative bacilli. In addition to supportive care, assessment for peripheral arterial disease, and surgical consultation for debridement, this patient requires broad-spectrum antibiotics directed against these pathogens, including methicillin-resistant Staphylococcus aureus. The best therapeutic choice includes vancomycin, which provides coverage against gram-positive organisms, and imipenem, which has excellent activity against gram-negative aerobic organisms and anaerobic bacteria.
Ceftazidime, a third-generation cephalosporin, and ciprofloxacin, a fluoroquinolone, are active against aerobic gram-negative bacilli including Enterobacteriaceae and Pseudomonas aeruginosa. However, they are not reliably active against gram-positive aerobic bacteria and anaerobes. The addition of vancomycin and metronidazole to either of these agents would provide adequate coverage.
Metronidazole provides coverage against anaerobic bacteria, and vancomycin provides coverage against aerobic gram-positive cocci. However, neither provides adequate coverage against aerobic gram-negative bacilli. The addition of ceftazidime, cefepime, or ciprofloxacin would provide this activity.
- Severe life-threatening diabetic foot infections are usually polymicrobial and require empiric broad-spectrum antibiotic coverage against aerobic gram-positive cocci, aerobic gram-negative bacilli, and anaerobic bacteria.
Correct answer: C. Mycobacterium abscessus.
This patient has a typical presentation for a soft tissue infection with a rapidly growing mycobacterium (RGM), Mycobacterium abscessus. This organism is found throughout the world and is endemic in the United States. Wound infection with RGM is uncommon but can be catastrophic if not recognized and treated appropriately. The most distinguishing characteristics of the infections are nodules, often purple in color, and chronic abscess or sinuses. Skin and subcutaneous infections with RGM should be strongly considered in clinical situations demonstrating chronic purulent drainage, a lack of a convincing pathogen on routine culture, and association with implanted prosthetic devices. A lack of response to treatment and the failure to isolate a convincing pathogen should prompt further diagnostic evaluation consisting of staining and special culturing for mycobacteria followed by sensitivity testing to determine the appropriate antimicrobial therapy.
Candida albicans might be considered as a causative agent in this setting, but this organism did not grow on the original culture and grew in only small amounts on subsequent cultures, suggesting that it was a colonizer selected by the antibiotic treatment. Other possible pathogens for such chronic draining skin infections include environmental fungi and Nocardia asteroides; however, these are not likely as nosocomial pathogens. Staphylococcus aureus is easily identified on routine culture and is almost always susceptible to vancomycin.
Inoculation infection with Mycobacterium tuberculosis might be a consideration in this patient; however, it occurs infrequently, even in endemic parts of the world, and is not particularly associated with rapidly progressive postoperative wound infections.
- Skin and subcutaneous infections with rapidly growing mycobacteria should be strongly considered in clinical situations demonstrating chronic purulent drainage, a lack of a convincing pathogen on routine culture, and association with implanted prosthetic devices.
Correct answer: C. A foam mattress overlay.
This patient has many risk factors for pressure ulcers, including advanced age, reduced mobility, inadequate nutrition, and urinary incontinence. The most appropriate preventive measure for this patient is a foam mattress overlay. A systematic review concluded that specialized foam mattresses/overlays and specialized sheepskin overlays reduce the incidence of pressure ulcers compared with standard hospital mattresses.
Since a targeted preventive approach to pressure ulcers is less costly than one focused on treating established ulcers, evaluation of patients by health care providers should include identifying patients at risk as quickly as possible. Expert opinion recommends the consistent use of a validated risk assessment tool, such as the Braden and Norton scales, supplemented by clinical judgment. Health care workers should regularly inspect the skin of patients at risk, and patients who are willing and able should be instructed to inspect their own skin.
Whether there is any additional advantage for ulcer prevention by using a “higher-tech” air-fluidized bed is unclear. These beds are much more expensive, are difficult to move, make nursing care more difficult, and are usually reserved for treating patients with established ulcers, mostly in a hospital setting.
The preferred seat cushion is one that distributes pressure uniformly over the weight-bearing body surface. Doughnut cushions do not do this and should not be used.
Avoiding friction, shear, and excessive skin moisture (for example, from perspiration, urinary or fecal incontinence, or excessive wound drainage) is important and should be part of routine care. Underpads on the bed or adult diapers, combined with consistent skin cleansing, are adequate for managing most patients with urinary incontinence. An indwelling or condom catheter is sometimes needed when treating an ulcer, but its use is probably unnecessary and potentially harmful in this patient with occasional incontinence. Massaging of pressure points adds to skin friction and increases the risk of early skin breakdown and should be avoided.
- Specialized foam mattresses/overlays reduce the incidence of pressure ulcers compared with standard hospital mattresses.
Correct answer: A. Capnocytophaga canimorsus.
This splenectomized patient most likely has overwhelming sepsis due to Capnocytophaga canimorsus, a member of the normal oral flora of dogs. Life-threatening infection with this gram-negative bacillus has been associated with dog bites in immunosuppressed patients, including those who have undergone splenectomy and those who abuse alcohol or have cirrhosis. The predisposition to infection with this organism in patients with asplenia is due to impaired ability to clear intravascular bacteria and impaired antibody production. The mortality rate is high in patients with C. canimorsus sepsis, requiring prompt management with antibiotics such as a β-lactam/β-lactamase inhibitor combination, supportive care, and possible surgical debridement.
Escherichia coli is not classically associated with dog bites.
Salmonella species have been associated with infections after contact with pet reptiles such as turtles and snakes. Gastroenteritis is a common feature of infection in these individuals and is not consistent with the symptoms found in this patient.
Staphylococcus aureus and Streptococcus pyogenes can cause necrotizing skin infections with associated shock; however, both are gram-positive cocci in contrast to the gram-negative bacilli that were isolated from the blood cultures of this patient.
- Capnocytophaga canimorsus should be suspected as a cause of sepsis in an asplenic patient or in a patient who abuses alcohol or has cirrhosis and has recently experienced a dog bite.