isolate of dog bites andPa. multocidasubsp. was the most common isolate of cat bites. Other
common aerobes include streptococci, staphylococci, Moraxella, and Neisseria. Common
anaerobes includeFusobacterium, Bacteroides,Porphyromonas, andPrevotella. Capnocytophaga
canimorsusis an invasive organism usually occurring in immunosuppressed patients after a
dog bite (41,42). Human bites are usually associated with mixed aerobic and anaerobic
organisms including Str. viridans and other streptococci, S. aureus, Eikenella corrodens,
Fusobacterium, andPrevotella. Clenched fist injuries may lead to infection, tendon tear, joint
disruption, or fracture (43). Clinicians should ensure that tetanus prophylaxis is current. The
local health department should be consulted about the risks and benefits of rabies
immunization (for treatment refer to Table 2).
NECROTIZING INFECTIONS
Necrotizing soft tissue infections are infrequent but highly lethal infections. They can be
defined as infections of any of the layers within the soft tissue compartment that are associated
with necrotizing changes. A high index of suspicion is necessary to make an early diagnosis of
necrotizing skin and soft tissue infections as in early stages distinguishing between a cellulitis
that should respond to antimicrobial treatment alone and a necrotizing infection that requires
operative intervention may be difficult.
Necrotizing Cellulitis
Infectious gangrene is a cellulitis that rapidly progresses, with extensive necrosis of
subcutaneous tissues and the overlying skin. Pathological changes are those of necrosis and
hemorrhage of the skin and subcutaneous tissue. In most instances, necrotizing cellulitis has
developed secondary to introduction of the infecting organism at the site of infection.
Streptococcal gangrene is a rare form caused by group A streptococci that occurs at the site of
trauma, but may occur in the absence of an obvious portal of entry. Cases may follow
infection at an abdominal operative wound, around an ileostomy or colostomy, at the exit of
a fistulous tract or in proximity to chronic ulceration. The organisms responsible include
Clostridium, Bacteroides,andPeptostreptococcus. The diagnosis is suggested when gas is
present or when necrosis develops rapidly in anarea of cellulitis. Gram-stain and culture of
skin drainage, aspirate fluid, or surgical specimens should reveal the pathogenic organisms
(44–46).
Treatment consists of immediate surgical exploration beyond the involved gangrenous
and undermined tissue. Areas of cutaneous necrosis are excised. Repeat exploration is
commonly performed within 24 hours. Antibiotic therapy should be guided by Gram stain
results or empirically consist of high-dose IV penicillin G (3–4 million units every 4 hours) or
ampicillin (2 g every 4 hours), with the addition of clindamycin.
Necrotizing Fasciitis
NF is a rapidly spreading infection that involves the fascia and subcutaneous tissue with
relative sparing of underlying muscle. The mortality of this disease remains alarmingly high
ranging from 6% to 76% (47). Delayed diagnosis and delayed debridement have been shown to
increase mortality. Some conditions appear to be more commonly associated with NF; these
include injection drug use and chronic debilitating comorbidities (e.g., diabetes mellitus,
immune suppression, and obesity). Type 1 NF is polymicrobial with at least one anaerobic
species isolated in combination with one or more facultative anaerobic species such as
nontypable streptococci and Enterobacteriaceae. Type 1 NFs are postoperative infections and
include Fournier gangrene. Type 2 NF is typically monomicrobial, most often caused by group
AStreptococcus(48) andClostridiumspp. There have been increasing case reports ofS. aureus
including community-acquired MRSA (CA-MRSA) being identified as a causative organism.
Other organisms that have rarely been implicated in monobacterial infections includeSerratia
marcescens,Flavobacterium odoratum,Ochrobactrum anthropi,V. vulnificus,Aeromonasspp., and
group G (49). NF presents either as an acute and life-threatening condition usually caused by
group AStreptococcusorClostridiumspp., or as a subacute process, usually caused by mixed
aerobic and anaerobic organisms. The primary site is the superficial fascia. Bacteria proliferate
within the superficial fascia and elaborate enzymes and toxins. The precise mechanism of
302 Sharma and Saravolatz