Subcutaneous abscess caused by Streptococcus pneumoniae sero
A 4-month-old girl was hospitalized with a swelling on her left thigh and an inability to move her left leg; she was afebrile. The patient was born by normal vaginal delivery after a full-term gestation and had no relevant medical history. The swelling of the left thigh appeared 1 week before hospitalization and gradually increased in size. The patient had received routine vaccination, including a second PCV-13 vaccination on her left thigh 1 month prior to hospitalization. After the vaccination, the patient did not have a fever, and the injection site was clear of any signs of infection; therefore, she was not followed up. On examination, the patient appeared alert and well. The patient did not move her left leg and cried on touching it. An erythematous, tender, and firm, but not fluctuant, skin lesion measuring 8?×?7 cm was detected on her left thigh. HIV screening showed negative results. Ultrasonographic imaging revealed a large subcutaneous hypoechoic fluctuant fluid-filled lesion measuring 8?×?7?×?4 cm. Magnetic resonance imaging revealed a large collection of subcutaneous fluid on the left thigh, with the absence of other diseases such as osteomyelitis or pyomyositis.

Based on her clinical symptoms and the imaging findings, the patient was diagnosed with a subcutaneous abscess. Incision of the subcutaneous abscess resulted in the drainage of a large volume of purulent material. Gram staining of the pus showed encapsulated gram-positive diplococci. The patient was treated with intravenous panipenem/betamipron (PAPM/BP). S. pneumoniae was isolated from the pus, while cultures from blood, skin, and nasopharyngeal samples were all negative. Because the pneumococcal isolate was susceptible to penicillin, PAPM/BP was replaced by intravenous ampicillin on Day 4 of hospitalization. The patient was discharged on Day 7 of hospitalization after full resolution of her illness without any residual sequelae.

The pneumococcal isolate was sent to the National Institute of Infectious Diseases and was identified as serotype 28F based on observation of Quellung capsule swelling. The serotype 28F was susceptible to penicillin, cephalosporins, carbapenems, quinolones, and macrolides.