Descending necrotizing mediastinitis caused by Group A Streptococcus associated with influenza A infection

Descending necrotizing mediastinitis (DNM), a severe complication arising from deep neck infection, developed in an obese 45-year-old Japanese male with diabetes. His condition was caused by a Group A Streptococcus (GAS) infection that arose following an earlier influenza A infection during a seasonal influenza outbreak. The patient had a good clinical course with surgical drainage and debridement with antibiotic treatment. Pre-existing medical conditions and co-infections such as influenza increase susceptibility to GAS infection, and invasive GAS infection leads to increased mortality. The patient initially presented with fever, sore throat, and cough following influenza A infection, symptoms that were difficult to distinguish from those of deep neck infection caused by GAS. As the GAS was detected in blood cultures, the initial diagnosis was primary bacteremia following influenza A. Subsequently, however, the appearance of erythema on the anterior neck and around the thyroid cartilage suggested a descending progression of the infection from the deep neck space. Contrast-enhanced CT led to a diagnosis of DNM. The reported cases of DNM associated with viral infections have so far been limited to those following varicella or Epstein-Barr virus (EBV) infection. To our knowledge, this is the first reported case of DNM caused by GAS associated with influenza A infection. DNM caused by GAS is a rare infection that requires prompt surgical intervention followed by thorough systemic management. Clinicians should carefully monitor patients with underlying medical conditions who manifest recurrent or new symptoms such as fever, sore throat, and dyspnea after influenza infection.