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The incidence of respiratory virus infection after hematopoietic cell transplantation (HCT) has probably been underestimated with conventional testing methods in symptomatic patients. This prospective study assessed viral infection episodes by testing weekly respiratory samples collected from HCT recipients, with and without symptoms reported by questionnaire, for 100 days after HCT. Samples were tested by culture and direct fluorescent antibody testing for respiratory syncytial virus (RSV), parainfluenza virus (PIV), and influenza A and B, and by quantitative reverse transcription–polymerase chain reaction for RSV, PIV, influenza A and B, and metapneumovirus (MPV). Of 122 patients, 30 (25%) had 32 infection episodes caused by RSV (5), PIV (17), MPV (6), influenza (3), RSV, or influenza (1). PIV, with a cumulative incidence estimate of 17.9%, was the only virus for which asymptomatic infection was detected. Lower virus copy number in patients with no or one symptom compared with 2 or more symptoms was found for all viruses in all patients (P < .001), with PIV infection having a similar virus-specific comparison (P = .004). Subclinical infection with PIV may help explain why infection-control programs that emphasize symptoms are effective against RSV and influenza but often not against PIV.

The importance of human metapneumovirus (hMPV), a recently discovered human respiratory virus, in hematopoietic cell transplant (HCT) recipients is not known. We retrospectively surveyed 211 bronchoalveolar lavage samples (BAL) from symptomatic adults with new or changing pulmonary infiltrates after HCT during five-year period using a quantitative real time RT-PCR assay. Medical records, radiographic studies, biopsy specimens, and autopsy material were reviewed. hMPV was detected in 8/211 (3.8%) BAL specimens from 5/162 (3%) patients. The median titer of hMPV was 9.0 x 106 copies/ml of BAL fluid (range 5.5 x 104 to 3.5 x 108). Persistent hMPV infection was noted in all 3 patients who had multiple samples tested. hMPV was also detected in lung tissue in 1 of 2 samples tested. Infected patients were between the ages of 24–54 years, and became symptomatic within the first 40 days post transplant. Initial symptoms included fever, cough, nasal congestion, and sore throat. Clinical findings near the time of diagnosis included respiratory failure, pulmonary hemorrhage, and culture-negative septic shock. Four patients died as a result of acute respiratory distress and pulmonary disease with clinical and autopsy diagnoses of “idiopathic pneumonia.” We conclude that hMPV infection is associated with respiratory failure in immunocompromised adults and may result in fulminant respiratory decompensation in the post transplant period. Prospective studies of the role of this virus in idiopathic pneumonia syndromes of immunocompromised patients are warranted.