Citrobacter koseri pneumonia as initial presentation of underlying pulmonary adenocarcinoma

Citrobacter koseri is a motile, gram-negative rod traditionally known to cause infection in individuals with significant comorbidities and immunocompromised status. While most cases represent nosocomial infections, rarely community-acquired infections have been reported. We present a previously healthy man in his 60s with C. koseri pneumonia who was subsequently found to have underlying pulmonary adenocarcinoma, illustrating the need for further investigation for immunodeficiency and/or intrapulmonary pathology.