A 23-year-old woman on postpartum day 10 develops a fever and left breast tenderness. What is the initial management step for her symptoms consistent with acute mastitis?

In the case of a postpartum woman presenting with fever and localized breast tenderness, consistent with acute mastitis, the initial management step is the initiation of antibiotic therapy, with dicloxacillin being the preferred choice.

Acute mastitis commonly occurs in breastfeeding women and is usually due to bacterial infection, often from Staphylococcus aureus. Dicloxacillin is effective against this organism and is the usual first-line antibiotic prescribed due to its good coverage for methicillin-sensitive strains and its ability to penetrate into breast tissue adequately.

While incision and drainage may be warranted in cases where there is an abscess or if symptoms do not improve with antibiotics, it is not the first step in uncomplicated mastitis. Mammography is generally not indicated in the immediate management of acute mastitis symptoms unless there are atypical features or if the symptoms persist despite treatment, which could raise suspicion for further complications. Tetracycline is not typically the first choice in this situation due to its potential adverse effects in breastfeeding women and coverage issues.

Thus, initiating treatment with dicloxacillin is the appropriate first step in managing this patient's symptoms of acute mastitis.