Facilitator Version
Module #13: Cellulitis / soft tissue infections / osteomyelitis
By Nicole Klein, MD
10/2013
Objectives:
1. Understand diagnostic evaluation and considerations for patients with cellulitis, soft
tissue infections and osteomyelitis.
2. Develop a management plan for patients with cellulitis, soft tissue infection or
osteomyelitis.
3. Understand potential complications of cellulitis, soft tissue infection, osteomyelitis.
References:
1. Infectious Disease Society of America (IDSA) guidelines: Practice Guidelines for the
Diagnosis and Management of Skin and Soft Tissue Infection, Published: Clinical
Infectious Diseases; 2005 ; 41 : 1373 -1406.
http://www.idsociety.org/Organ_System/#sthash.3TmbNdTL.dpuf
2. IDSA guidelines: Diagnosis and Treatment of Diabetic Foot Infections, Clinical
Infectious Diseases ; 2012 ; 54 : e132 -e173
http://www.idsociety.org/Organ_System/#sthash.3TmbNdTL.dpuf
3. IDSA Guidelines: Management of Patients with Infections Caused by MethicillinResistant Staphylococcus Aureus: Clinical Practice Guidelines by the Infectious Diseases
Society of America (IDSA).
http://www.idsociety.org/Organ_System/#sthash.3TmbNdTL.dpuf
4. International working group on the diabetic foot:
http://iwgdf.org/consensus/infection-in-the-diabetic-foot/
5. MKSAP 16
Case:
63 year old male nursing home resident with hypertension, coronary artery disease, hyperlipidemia, and
diabetes mellitus complicated by peripheral neuropathy presented with 6 month history of foot ulcer, 7 day
history of purulent discharge from ulcer, and 2 days of fever and redness progressing from toes to his lower
leg.
On physical exam, temperature 38.2, heart rate 100 beats/min, blood pressure 108/72, respirations 14. On the
lateral aspect of the right great toe, there is a 2 cm x 1.5 cm ulcer, probing to 3 mm deep, with purulent
material at its base. There is no visible or palpable bone at base of ulcer, and no palpable fluctuance. The
edges of the ulcer are irregular and raised, with induration, warmth, and tenderness extending over the
dorsal foot to the base of the right ankle. Peripheral pulses are +2 in bilateral posterior tibial and +1 in
bilateral dorsalis pedis. Capillary refill is slow bilaterally.
Labs: wbc 16 (82% neutrophils), hct 36, plt 356. HbA1c is 11.2. Chemistry shows sodium 138, potassium 4,
chloride 100, bicarbonate 24, bun 22, cr 1.4, glucose 228. Admission MRSA screening swab is positive.
Plain xray of the foot shows soft tissue defect, no gas in the soft tissue, no underlying cortical bone erosion.
What is the diagnosis and what other testing would you consider before starting treatment?
1.
2.
Meets SIRS criteria (temperature > 38, HR >90, WBC > 12,000) and sepsis criteria given known
source.
Diabetic foot infection. With above data, appears to be soft tissue infection, without current clinical
(doesn’t probe to bone) or radiographic (xray negative for bony erosion) evidence of osteomyelitis.
What should be done before starting antibiotics:
Blood cultures x 2, aerobic and anaerobic wound culture (if deep wound culture or tissue debridement available).
Interpret superficial wound swabs / cultures with caution. Studies have shown (senneville et al 2006 clin infect dis)
only 22.5% concordance between superficial wound culture and bone biopsy cultures in patients with osteomyelitis.
Same study shows Staph Aureus with highest concordance of 42%, so cover this if found on wound culture.
What empiric antibiotic regimen would you start?
Empiric regimen should be based on clinical severity classification from IDSA guidelines or diabetic foot 2004:
-mild infection: > 2 of the following: purulence, erythema, pain, tenderness, warmth, induration, cellulitis extending
<2 cm from ulcer, no deep tissue infection, no systemic illness. Outpatient oral antibiotics ok with coverage of Staph
and Strep. Cover MRSA if purulent or risk factors for MRSA (known previous infection or colonization, LTAC,
recent hospitalization or antibiotic use)
-moderate infection: meets criteria above for mild infection + not systemically ill and meets >1 of these: > 2cm
cellulitis from ulcer, lymphangitic streaking, deep tissue abscess or infection, gangrene, involvement of muscle,
tendon, joint or bone. Empiric therapy includes staph and strep skin flora, MRSA if risk factors present, and gram
negative rods + anaerobes. Can be oral. Should be IV if deep tissue involvement suspected. Include pseudomonal
coverage if macerated ulcer or exposure to water.
-severe infection: patient has systemic toxicity or metabolic abnormality (leukocytosis, acidosis, severe
hyperglycemia, azotemia). Treat with broad spectrum antibiotic coverage including gram positive skin flora, gram
negative rods, anaerobes. Include MRSA therapy. Surgical evaluation for debridement.
*Examples of appropriate regimens: see attached tables
Most common flora in diabetic foot infections:


superficial acute ulcers: skin flora including gram positive cocci: staph aureus, strep agalactiae, strep
pyogenes, coag negative staph.
deep or chronic ulcers, or previously treated: polymicrobial including skin flora as mentioned above,
enterococci, gram negative enterics, pseudomonas, anaerobes
What other therapies are indicated?
Fluids, electrolyte management, blood sugar control, wound care, nutrition, consider surgical evaluation for
debridement and/or bone biopsy if osteomyelitis suspected. Check ESR and CRP for baseline to monitor response
to therapy.
The patient is started on Unasyn and Vancomycin, blood sugar is monitored closely and controlled, podiatry
is consulted and debrides the ulcer at bedside with deep tissue cultures sent. Gram stain shows mixed skin
flora, with predominance of gram positive cocci in chains, several species of gram negative rods. After 48
hours, the patient remains intermittently febrile, normotensive, with no appreciated regression in cellulitis,
and persistent pain. There is some decreased purulence after wound debridement, but white blood cell count
remains persistently elevated at 15,300.
What may be contributing to slow response to therapy? Is further workup and/or a change in antibiotics
needed?
Consider deeper infection (osteo or abscess) or resistant organism. Suspect osteo if: ulcer >2cm, exposed bone,
ESR > 70 , ulcer present > 2 weeks (Butalia S, et al. JAMA 2008; 299:806. ). Consider MRI to eval for abscess or
underlying osteomyelitis. Gold standard for osteomyelitis is bone bx with positive bone culture and histopathologic
bone changes consistent with osteomyelitis.
Consider changing antibiotics. Gram positive cocci in chains is likely streptococcal infection. Unasyn should cover
this. However the gram negative rods could be resistant flora (pseudomonas or other resistant gram negative?).
Could he have an ESBL (extended spectrum beta lactamase) producing organism? Usually klebsiella spp or E.coli,
but also other gram negatives including proteus, pseudomonas, serratia, citrobacter and others. Risk factors for
ESBL: prolonged hospital stay, prolonged venous or arterial catheter, prior abx, g or j tube, urinary catheter,
ventilator, hemodialysis, residency in LTAC. Some ESBLs susceptible to cefepime or zosyn, but for severe
infections clinical outcomes shown to be better with carbapenem . In this case, as patient no longer septic, might
broaden to zosyn while cultures pending. If he worsened, then carbapenem.
Consider ABI to evaluate arterial supply to feet? If poor blood flow, antibiotics may not be able to reach site in
adequate concentration. Consider Doppler to r/o DVT?
Warning signs for more serious infection (nec fasc?): failure to respond to broad spectrum therapy, rapid spreading,
gas in soft tissue on xray, bullae.
Unasyn is broadened to Zosyn pending culture results. MRI and ABIs are ordered. The next day, MRI shows
deep tissue abscess 4 cm x .5cm without evidence of osteomyelitis. ABIs are 1.2 bilaterally (normal). Deep
wound culture now shows strep pyogenes and e.coli resistant to unasyn, but sensitive to zosyn. What is your
next step?
Note, antibiogram for the VA can be found on the VA home page (search for it). Antibiogram from 2012 shows
69% of E.coli found at the VA is resistant to Unasyn.
Zosyn is appropriate and should be continued. Discontinue vancomycin (no MRSA isolated). Patient needs surgical
drainage of abscess collection.
The patient is taken to the OR for abscess debridement the next day. In the next 24 hours he defervesces,
wbc trending down to 12, pain is improving, and erythema/induration is receding. What would be an
appropriate course of therapy now?
Because there was no osteomyelitis, and this is a skin/soft tissue infection Zosyn can be converted to an oral
regimen based on culture results when patient is clinically improving. Generally, antibiotics should be continued to
complete a 14 day course, based on clinical response to therapy with ongoing wound care, blood sugar control, etc.
If there had been evidence for osteomyelitis, how long would the patient be treated with antibiotics?
Generally osteomyelitis is treated with 6 weeks of iv antibiotics.
The patient responds well to antibiotics, with no further signs of infection at 14 days. Antibiotics are then
discontinued and wound care continued until the ulcer heals 4 weeks later.
6 months later the patient develops an ulcer on the heel of the other foot. He is followed weekly in podiatry
clinic. Despite wound care, the ulcer fails to resolve. After 2 months of wound care, the podiatry resident
notes the ulcer is now probing to bone in clinic and orders a foot x-ray which shows cortical erosion of
calcaneal bone. You are called to evaluate the patient for further workup. The calcaneal ulcer is without
purulence, no surrounding erythema, and the patient is afebrile with normal vitals. What would be the first
steps in management?
As the patient is clinically stable, without signs of cellulitis or systemic signs of infection, holding off on antibiotics
while bone biopsy is performed would be appropriate. Bone biopsy should be submitted for gram stain, bacterial and
fungal cultures, and pathology for clean bone margins (if curative resection of infected bone is attempted). After
bone biopsy, broad spectrum antibiotics would be appropriate, which can be modified based on bone culture results.
In this patient, given recent treatment for infection of the other foot, frequent contact with healthcare system, and
known prior MRSA carrier status, empiric MRSA coverage would be appropriate. If no MRSA on bone culture
performed prior to antibiotic treatment, then MRSA coverage can be discontinued.
MKSAP 16 Infectious Disease questions:
*none that specifically address diabetic foot infection.
*questions regarding skin and soft tissue and bone infection:
#7 chronic OM and septic joint, answer B
#39 diagnosis of OM with imaging, answer A
#63 diagnosis of OM with bone bx, Answer A
# 84 in-patient tx of purulent cellulitis, Answer A
#102 out patient tx of non-purulent cellulitis, Answer A