Human metapneumovirus infection in the Canadian population

Abstract

Human metapneumovirus (hMPV), a newly discovered paramyxovirus, has been associated with acute respiratory tract infections (ARIs) ranging from upper ARIs to severe bronchiolitis and pneumonia. Important questions remain on the contribution of hMPV to ARIs and its impact on public health. During the 2001-2002 season, we conducted a collaborative study with four provincial public health laboratories to study the prevalence of this new virus in the Canadian population. A total of 445 specimens were collected from patients of all age groups with ARIs and were tested for the presence of hMPV by reverse transcription-PCR. Of these, 66 (14.8%) tested positive for hMPV. Positive specimens were found in all age groups and in all four provinces studied. Virus activity peaked in February and March. The age range of the patients with hMPV infection was 2 months to 93 years (median age, 25 years), with similar numbers of females (35%) and males (41%). Thirty-three percent (n = 22) of hMPV-infected patients were hospitalized; of these, 27% (n = 6) had rhinitis and pneumonia, 23% (n = 5) had bronchiolitis, and 9% (n = 2) had bronchitis. The hospitalization rates were significantly higher among patients <5 years of age (P = 0.0005) and those >50 years of age (P = 0.0044) than among those 6 to 50 years of age. Phylogenetic analysis of the F gene showed that two hMPV genetic clusters were cocirculating in the 2001-2002 season, and comparison with earlier studies suggests a temporal evolutionary pattern of hMPV isolates. These results provide further evidence of the importance of hMPV in ARIs, particularly in young children and elderly individuals.

FIG. 1.

Number of hMPV-positive specimens per month in the 2001-2002 season.

FIG. 2.

Clinical symptoms and diagnoses reported in hMPV-positive patients.

FIG.3.

Phylogenetic analysis of hMPV isolates. The sequences of nucleotides 688 to 1032 of the F gene were determined. The corresponding gene sequences of previously reported Canadian and Dutch hMPV isolates were also included. Phylogenetic analysis was performed by the neighbor-joining method of the MEGA program. The previous Canadian isolates are indicated by CAN followed by the year of collection and the isolate number (e.g., CAN97-83). The isolates presented in this study are indicated by the isolate number and the year (e.g., 172-02). The Dutch isolate is indicated by NDL00-1.