Overview of Bacterial Skin Infections

Bacterial skin infections can be classified as skin and soft-tissue infections (SSTI) and acute bacterial skin and skin structure infections (ABSSSI).

SSTI include:  

• Carbuncles

• Ecthyma

• Erythrasma

• Folliculitis

• Furuncles

• Impetigo

• Lymphadenitis

• Minor cutaneous abscesses

ABSSSI are complex bacterial skin infections. They include:

• Cellulitis

• Erysipelas

• Lymphangitis

• Major cutaneous abscesses (> 75 cm² including edema, erythema, and induration)

• Necrotizing soft-tissue infection

• Wound infections

Staphylococcal scalded skin syndrome, scarlet fever, and toxic shock syndrome are skin-related complications of bacterial infections.

The global annual incidence rate of bacterial skin infections has been increasing since 1990, with an average annual increase of approximately 0.6% (1). These infections are substantially more prevalent outside the United States, with the highest prevalence in resource-limited regions, particularly sub-Saharan Africa and Pacific Island nations. Children < 5 years of age and adults > 85 years of age are particularly at risk.

The primary pathogens in SSTI are Streptococcus and Staphylococcus species, including methicillin-resistant Staphylococcus aureus (MRSA). MRSA is a common pathogen in the United States. However, the proportion of cases attributed to MRSA differs substantially elsewhere in the world. Because MRSA can be resistant to multiple antibiotics, recommended antibiotics for bacterial SSTI depend largely on local prevalence and resistance patterns of MRSA.

Mild to moderate purulent ABSSSI can be treated with a beta-lactam, clindamycin, trimethoprim/sulfamethoxazole, or doxycycline (Mild to moderate purulent ABSSSI can be treated with a beta-lactam, clindamycin, trimethoprim/sulfamethoxazole, or doxycycline (2). It is worth noting that, in the United States, between 2013 and 2023 there was a substantial increase in the rate of clindamycin resistance in group A streptococci (eg, S. pyogenes) from 12.5% to 26.4% (3). Additional coverage for MRSA in nonpurulent ABSSSI should be considered in patients at increased risk (eg, after penetrating trauma, with suspected nasal MRSA carriage, injection drug use).

Severe nonpurulent ABSSI, defined by the presence of signs of systemic toxicity (eg, fever, tachycardia, tachypnea, delirium, marked leukocytosis, acute end organ dysfunction), require surgical inspection to rule out a necrotizing process. In these infections, Gram stain and culture with antibiotic susceptibility testing are also recommended. Empiric therapy typically includes vancomycin and broad-spectrum gram-negative and anaerobic coverage such as piperacillin/tazobactam or a carbapenem such as imipenem or meropenem (Severe nonpurulent ABSSI, defined by the presence of signs of systemic toxicity (eg, fever, tachycardia, tachypnea, delirium, marked leukocytosis, acute end organ dysfunction), require surgical inspection to rule out a necrotizing process. In these infections, Gram stain and culture with antibiotic susceptibility testing are also recommended. Empiric therapy typically includes vancomycin and broad-spectrum gram-negative and anaerobic coverage such as piperacillin/tazobactam or a carbapenem such as imipenem or meropenem (2).