The patient was a man in his 80s. PCR test was performed after he developed a fever, and the result was positive for SARS-CoV-2 infection. On admission, CT showed ground-glass opacities and consolidation in both lung fields, leading to a diagnosis of COVID-19 pneumonia. The fever promptly resolved after starting treatment with dexamethasone 6.6 mg injection, but high fever returned the day after discontinuing dexamethasone. We considered bacterial pneumonia as a complication, but antibiotics were ineffective. We suspected cytokine storm and began steroid pulse therapy. The fever temporarily resolved but returned when the steroid dose was reduced. In the differential diagnosis, we considered opportunistic infections such as fungal infection and cytomegalovirus infection, pulmonary tuberculosis, and non-infectious lung diseases such as idiopathic organizing pneumonia. Examination and treatment were performed with these in mind. Finally, we diagnosed pulmonary tuberculosis and cytomegalovirus infection, and treatment was started for each. He was subsequently transferred to a treatment facility for patients with tuberculosis. Steroids are a key drug in the treatment of COVID-19, but they may reduce immune function and increase susceptibility to infection, so caution is required for various infectious diseases.