Cellulitis and erysipelas: Clinical sciences

Cellulitis and erysipelas are acute infections of the skin and subcutaneous tissues. Erysipelas is an infection of the upper layer of the dermis with the superficial lymphatics and vessels, while cellulitis affects the deeper layers of the dermis and the subdermal tissues. These infections usually occur when bacteria enter through breaks in the skin barrier, such as a laceration and puncture wound. The vast majority of infections are caused by beta-hemolytic Streptococci, such as Group A Streptococcus or Streptococcus pyogenes; as well as Staphylococcus aureus including methicillin-resistant or MRSA. While erysipelas is usually limited to the skin, cellulitis can sometimes present with or without systemic symptoms.

When approaching an individual with signs and symptoms suggestive of cellulitis and erysipelas, first obtain a focused history and physical examination. Alright, let’s start with erysipelas. On history, the patient might report an acute onset of skin redness, swelling, and pain usually around the face or the extremities. Notably, there won’t be systemic symptoms like fever and chills, and this is one of the main factors distinguishing erysipelas from cellulitis. A physical exam typically reveals a well-demarcated area of erythema with superficial induration that is warm and tender to touch.

Because erysipelas is a local infection, you can start the patient on oral antibiotics such as a penicillin or first-generation cephalosporin. Then, assess the response at 24 to 48 hours. If the patient shows adequate response, in other words, erythema, induration, and pain have improved, they can continue the current treatment and complete the course of antibiotics. However, if the patient has an inadequate response, assess for signs of spreading infection or abscess and consider switching the antibiotics to broaden the coverage.

Alright, now that patients with erysipelas are treated, let’s go back to history and physical and talk about patients with more severe signs of infection. Similar to erysipelas, the patient might report skin redness, swelling, and pain over the affected area. However, they may or may not present with systemic symptoms, such as fevers or chills.

On physical exam, the area of erythema is typically not well-demarcated, and induration might not always be present. Additionally, you can expect the erythematous area to feel warm to the touch or tender on palpation. If you see these findings, you should suspect cellulitis. The next step is to assess for systemic signs and symptoms. If the patient does not have either of those features, they have cellulitis without systemic symptoms.

Here is a clinical pearl for you! During the physical exam, mark the edges of the erythema with a pen. This will help you assess if the area of redness is spreading or not.

Now that you have made your diagnosis, let’s talk about management. As before, you should start the patient on empiric oral antibiotics, such as penicillin or first-generation cephalosporin. When starting antibiotics, consider coverage for beta-hemolytic Streptococci and methicillin-sensitive Staphylococcus aureus, which are the two most common pathogens of cellulitis. You should cover for MRSA in patients who have risk factors, such as recent hospitalization, purulent drainage, or prior MRSA infection. If you think the patient might have MRSA, you can treat them with Trimethoprim-Sulfamethoxazole.

Now once you've started antibiotics, your next step is to assess for a response. Patients with cellulitis typically show improvement at 24 to 48 hours of beginning antimicrobial therapy. If the patient is responding adequately to treatment, evidenced by improvement in symptoms like pain and redness, you can complete the course of antibiotics.