Background:Red breast syndrome (RBS) has been described as an erythema that may be associated with 2-stage prosthetic reconstructive breast surgery using biologic mesh. RBS is differentiated from infectious cellulitis through absence of fever and laboratory abnormalities and usually has a self-limiting course. There have been no clinical reports on etiology, risk factors, or management of RBS. This report describes patient data that raise the need to rule out mycobacterial infection when RBS is being considered as a diagnosis.Methods:We present 6 cases of Mycobacterium fortuitum infection occurring after prosthetic breast reconstruction performed with a human-derived acellular dermal matrix, including the timing and course of erythema, laboratory results, treatments used, and long-term outcomes. We also describe the differential diagnoses of RBS in the context of these cases, including emergence of acid-fast bacilli and diagnostic and treatment considerations. Exact two-tailed 95% confidence intervals based on the F-distribution are provided with estimates of the incidence rates of infection.Results:The 6 cases presented here do not fit the typical description of RBS and were caused by mycobacterium infection. Statistical evaluation of the estimated incidence rate of M. fortuitum infection in a patient thought to have RBS, which occurred 100% of the time in this series, revealed a 95% confidence interval of 54.1–100%.Conclusions:When presented with possible RBS, surgeons must rule out cellulitis, culture for acid-fast bacilli such as mycobacterium species, and then determine the best course of treatment. Patient counseling regarding potential household sources of infection is warranted to minimize postoperative infection risk.