A 19-year-old woman was referred and admitted to our hospital because of a progressive fever and persistent cough. The patient was a university student who lived with her parents, brother, and grandmother. Her medical history was uninformative regarding risk factors; the patient had no smoking history. She had not received influenza vaccination during the season. Six days prior to admission, she experienced fever and visited a clinic. There had been an outbreak of influenza A and B virus infections in the area during that time. Aside from this, she had no episodes of exposure to pathogens causing acute fever. The nasopharyngeal swab sample was analyzed using a rapid test kit and did not indicate the presence of either type A or B influenza virus antigen. Repeated examination of a nasopharyngeal swab sample on the following day did not indicate any influenza virus antigen. Clarithromycin was administered based on a diagnosis of acute upper respiratory infection. As there was no clinical improvement in spite of five days of treatment, the patient was referred to our hospital.
At admission, a physical examination indicated that the patient was a well-developed and well-nourished woman. Her body temperature was 39.6 C, blood pressure was 108/65 mm Hg, pulse was 106 beats/min, respiratory rate was 24 breaths/min, and room air percutaneous oxygen saturation (SpO2) was 95%. The physical examination was unremarkable, and her respiratory sound was normal.
An initial laboratory examination showed a white blood cell count of 5,200/microL (70% neutrophils), C-reactive protein level of 18.58 mg/dL, and procalcitonin level of 0.63 ng/mL (normal range <0.5 ng/mL). A nasopharyngeal swab sample analyzed using a rapid test kit (Quick Chaser Flu A, B; Mizuho Medy Co., Saga, Japan) indicated the presence of influenza B virus antigen. Stained sputum smears revealed Gram-positive cocci and Gram-negative rods. No pathogenic bacteria were cultured form repeated blood or sputum cultures. Chest radiography and CT scan (Figure 1) showed dense consolidation in the left upper lobe, indicating the presence of lobar pneumonia. The patient was diagnosed with influenza B virus infection accompanied by community-acquired pneumonia. The patient was treated with peramivir (600 mg/day) and sulbactam/ampicillin (SBT/ABPC; 12 g/day).
Following admission, the patient's fever persisted, and her respiratory condition worsened. The course of the patient's illness is shown in Figure 2. On day 3 after admission, her body temperature was 40.0 C, and a laboratory examination showed no improvement. Therefore, ciprofloxacin (CPFX; 600 mg/day) was added. On day 5, the high fever persisted, and the room air SpO2 was 88%. A chest CT scan revealed extension of the consolidation areas with air bronchogram in the left upper lobe and opacities in the right lung (Figure 3). On day 6, the SBT/ABPC and CPFX treatment was changed to meropenem (MEPM; 3 g/day) and levofloxacin (LVFX; 500 mg/day). On day 8, the patient's physical condition gradually improved, and the SpO2 recovered to >95% without oxygen administration. The sputum sample analyzed using a loop-mediated isothermal amplification assay (Mitsubishi Chemical Medience Co., Tokyo, Japan) revealed the presence of M. pneumoniae-specific DNA. There was no outbreak of M. pneumoniae infection in the area at the time. On day 13, the patient became afebrile and was discharged. The serum antibody titer against M. pneumoniae was 1 : 160 on admission and 1 : 10,240 on day 18 using the particle agglutination method and 1 : 32 on admission and 1 : 1024 on day 18 using the complement fixation test. In addition, the serum antibody titer against influenza B virus, measured using the complement fixation test, was <4 on admission and 1 : 128 on day 18. The serum antibody titer against influenza A virus did not increase throughout the clinical course.