Subcutaneous abscess caused by Streptococcus pneumoniae sero
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The detection of Streptococcus pneumoniae in culture from samples obtained from a normally sterile site is known as invasive pneumococcal disease (IPD). Pneumococcal conjugate vaccines (PCV) have been developed for the prevention of highly virulent serotype-induced IPD. There has been a rapid increase in the occurrence of IPD caused by non-vaccine serotypes despite the successful reduction of IPD caused by vaccine serotypes following the introduction of PCV, and serotype substitution has become a global concern.

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 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.

On examination, the patient appeared alert and well. She had normal vital signs. 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. Laboratory investigations revealed leukocytosis. USG imaging revealed a large subcutaneous hypoechoic fluctuant fluid-filled lesion measuring 8 × 7 × 4 cm. MRI revealed a large collection of subcutaneous fluid on the left thigh, with 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). 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.

A typical paediatric skin and soft tissue infection is a subcutaneous abscess, while pneumococcal subcutaneous abscesses are very rare. As a subcutaneous abscess was caused by pneumococcal serotype 28F, this serotype may have high virulence. The incidence of IPD caused by non-vaccine serotypes, such as 28F, is expected to increase in the future.