Why would a patient with Streptococcus A (Strep A) infection and rash experience a worsening rash at day 10?

From the Guidelines

A patient with strep A infection and rash who experiences worsening of the rash around day 10 is likely developing a delayed immune reaction called post-streptococcal reactive phenomenon, most commonly scarlet fever or a serum sickness-like reaction. This occurs as the body's immune system responds to streptococcal antigens even as the infection itself may be resolving. The worsening rash may represent either inadequate antibiotic treatment allowing persistent infection, or more commonly, an immune-mediated reaction that occurs despite appropriate antibiotic therapy. Treatment should include completing the full course of antibiotics (typically penicillin V 500 mg twice daily for 10 days or amoxicillin 500 mg three times daily for 10 days) if not already finished, as recommended by the Infectious Diseases Society of America 1. Supportive care with antihistamines like diphenhydramine 25-50 mg every 6 hours as needed for itching may help manage symptoms. In severe cases with significant systemic symptoms, a short course of corticosteroids might be considered, as suggested by guidelines for the management of skin and soft-tissue infections 1. This delayed reaction occurs because streptococcal proteins can cross-react with human tissues, triggering immune responses that manifest as skin eruptions even after the bacteria are being cleared from the body. It is essential to note that the use of antibiotics should be guided by the principles of high-value care, which emphasize the importance of appropriate antibiotic use for acute respiratory tract infections in adults, as advised by the American College of Physicians and the Centers for Disease Control and Prevention 1. Key considerations in managing this condition include:

• Completing the full course of antibiotics as prescribed
• Providing supportive care for symptoms such as itching
• Considering the use of corticosteroids in severe cases
• Following guidelines for the management of skin and soft-tissue infections
• Adhering to principles of high-value care in antibiotic use.

From the Research

Worsening Rash in Patients with Strep A and Rash

• A worsening rash at day 10 in a patient with Strep A and rash could be due to various factors, including the natural course of the illness or a potential allergic reaction to the antibiotic treatment 2, 3.
• The provided studies do not specifically address the issue of a worsening rash in patients with Strep A and rash, but they do discuss the treatment and management of streptococcal pharyngitis 2, 3, 4, 5, 6.
• According to the study by 5, patients with worsening symptoms after appropriate antibiotic initiation or with symptoms lasting 5 days after the start of treatment should be reevaluated, which may be relevant to the patient's worsening rash.
• Another study by 4 mentions that antibiotics can affect the bacterial ecology, encouraging resistance among some bacterial species, which could potentially lead to a worsening rash, although this is not directly stated in the study.
• The study by 6 compares the treatment of streptococcal pharyngitis with once-daily amoxicillin versus intramuscular benzathine penicillin G, but does not specifically address the issue of a worsening rash.
• Overall, the provided studies do not offer a clear explanation for the worsening rash at day 10 in a patient with Strep A and rash, and further evaluation and investigation may be necessary to determine the cause and appropriate treatment 2, 3, 4, 5, 6.