Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (84 page)

Up to 75% of purulent skin/soft tissue infxns, depending on local epi (rapidly increasing)

Clinically indistinguishable from MSSA, often assoc. w/ purulent drainage or exudate

High-risk groups: athletes, military, prison, MSM, communities w/ high prevalence

Often TMP-SMX sensitive; variably clindamycin sensitive (may falsely appear susceptible on lab testing, requires confirmation w/ D-test;
NEJM
2007;357:380)

• Erythema, edema, warmth, pain (rubor, tumor, calor, dolor) • Lymphangitis (proximal red streaking) and regional lymphadenopathy •
Toxic shock syndrome
can occur w/ staph or strep infxn. Fever, HA, N/V, diarrhea, myalgias, pharyngitis, diffuse rash w/ desquamation, HoTN, shock. BCx may be
.

• Bites: skin and oral flora (incl anaerobes) + special exposures:

Diagnosis

• Largely clinical diagnosis; BCx low yield (Se <5% in simple cellulitis) but useful if

• Aspirate of bulla or pus from furuncle or pustule may provide microbiologic dx
Treatment

•
Limb elevation
; erythema may
worsen
after starting abx b/c bacterial killing → inflam.

• I&D if abscess is present in addition to cellulitis • Worse outcomes if vasc. insuff., edema, immunosupp., resistant orgs. or deeper infxn • In obese Pts, adequate drug dosing important to avoid treatment failure (
J Infect
2012;2:128)

OTHER CUTANEOUS INFECTIONS

“DIABETIC FOOT” = INFECTED NEUROPATHIC FOOT ULCER

Leading cause of DM-related hosp. days & nontrauma amputations
Microbiology

•
Mild
(superficial, no bone or joint involvement): usually
S. aureus
or aerobic streptococci •
Limb-or life-threatening
= deep, bone/joint involvement, systemic tox., limb ischemia • Mono-or polymicrobial with aerobes + anaerobes

aerobes =
S. aureus
, strep, enterococci and GNR (including
Pseudomonas
)

anaerobes = anaerobic streptococci,
Bacteroides
,
Clostridium
(rare)

Clinical manifestations

• Clinical dx: ≥2 classic s/s of inflammation (erythema, warmth, tenderness [may be absent in neuropathy], pain or induration) or purulent secretions ± crepitus (indicating gas and ∴ mixed infection w/ GNR & anaerobes or
Clostridium
) • Complications: osteomyelitis, systemic toxicity (fever, chills, leukocytosis, hyperglycemia)
Diagnostic studies

• Avoid superficial swabs (
only
helpful if
for
S. aureus
and suspect infxn);
wound cx
(eg, deep tissue sample or curettage at ulcer base after débridement) has ↑ Se • Blood cx should be obtained in all Pts,
in 10–15%

•
Osteomyelitis should always be ruled out
: probe to bone test for all open wounds in a diabetic foot (high Sp but low Se); imaging (see below);
bone biopsy
best
Treatment
(
CID
2012;54:e132)

• Elevation, non–weight-bearing status,
wound care
, glycemic control,
antibiotics

• Evaluation and treatment for venous insufficiency and arterial ischemia •
Many require surgery
: early, aggressive and repeated débridement; revascularization or amputation may be necessary • Management by multidisciplinary team improves outcomes (
Circulation
2006;113:e463)

NECROTIZING FASCIITIS

Definition

• Infection and necrosis of superficial fascia, subcutaneous fat and deep fascia (necrosis of arteries and nerves in subcutaneous fat → gangrene) • Fournier’s gangrene: necrotizing fasciitis of the male genitalia or female perineum
Epidemiology

• Affects healthy individuals but ↑ risk: DM, PVD, EtOH abuse, IDU, immunosupp., cirrhosis
Microbiology

• Type I (after abd/perineal surgery or trauma; in DM, PVD): polymicrobial (w/ anaerobes) • Type II (usually extremities):
Strep pyogenes
±
CA-MRSA
, often healthy w/o obvious portal of entry; up to
¹
/
₂
have toxic shock syndrome (TSS)
Clinical manifestations

• Need
high degree of clinical suspicion
because of nonspecific physical exam • Most common sites: extremities, abdominal wall and perineum, but can occur anywhere •
Cellulitic skin
D
s
with poorly defined margins +
rapid spread + systemic toxicity
•
Pain out of proportion
to apparent cellulitis; skin hyperesthetic and later anesthetic •
Bullae, darkening of skin to bluish-gray ± crepitus
or radiographically visible gas
Diagnostic signs

• Clinical dx sufficient to initiate
urgent surgical exploration
• Aspiration of necrotic center; BCx; Gram stain; ✓ CK for tissue necrosis

• Imaging:
non-contrast CT
, but do not delay therapy (
Arch Surg
2010;145:452) • Microbiologic dx from Gram stain and culture of surgical specimens

Treatment

• Definitive treatment is
surgical débridement
of necrotic tissue and fasciotomy • Type I: breadth of GNR coverage determined by host, prev hosp, prev Rx and initial