A successfully treated case of parainfluenza virus 3 pneumonia mimicking influenza pneumonia.

Influenza infection is the most common viral infection causing respiratory illness. Influenza pneumonia is the most severe complication of influenza virus infection, resulting in high mortality.(1) Although seasonal influenza viruses are commonly detected by rapid antigen testing of nasopharyngeal swabs, a swine flu virus (H1N1) is rarely isolated.(1) Therefore, anti-influenza therapy should be started empirically if influenza pneumonia is suspected. It is known that parainfluenza virus (PIV) caused influenza-like illness during the swine influenza pandemics.(2) It has been reported that PIV type 3 (PIV3) can cause pneumonia in immunosuppressed patients, such as adult transplant recipients.(3) We report a successfully treated case of PIV3 pneumonia mimicking influenza pneumonia in a 31-year-old female patient with asthma. The patient had high fever (39.5°C), general fatigue, systemic joint pain, and anorexia for two days before being referred to our medical center. She was a current smoker and had a history of smoking (20 pack-years) and of bronchial asthma (no current use of medication). The patient also had poorly controlled diabetes mellitus and a body mass index of 30 kg/m2. A chest X-ray revealed diffuse ground-glass opacities in both lungs (Figure 1). Laboratory tests showed severe inflammatory reaction (C-reactive protein = 19.2 mg/dL and ESR = 83 mm/h). She had severe respiratory failure and an SpO2 of 80% on room air at the first visit, and oxygen therapy was started with noninvasive positive pressure ventilation. Because of the severe respiratory failure, bronchoalveolar lavage was not performed. Although the result of a rapid influenza antigen detection test was negative, she was diagnosed with influenza pneumonia on the basis of influenza-like symptoms and radiological findings, such as diffuse groundglass opacities (Figure 2). The patient was started on empirical treatment with peramivir (600 mg/day) for 5 days (for the influenza infection) combined with a steroid pulse and i.v. erythromycin (1,000 mg/day) for 5 days (for the acute respiratory failure). Her respiratory function gradually improved, and noninvasive positive pressure ventilation was discontinued on day 5. Oral prednisolone was then started (at 80 mg/day), and the dose was tapered, being modified once every three days, as follows: to 40 mg/day on day 6; to 30 mg/day on day 9; to 15 mg/day on day 12; and discontinuation on day 15. The patient was discharged on day 18. Although she tested negative for influenza A and influenza B antibodies, the patient tested