Human metapneumovirus and lower respiratory tract disease in otherwise healthy infants and children

BACKGROUND

We sought to determine the role of human metapneumovirus in lower respiratory tract illness in previously healthy infants and children.

METHODS

We tested nasal-wash specimens, obtained over a 25-year period from otherwise healthy children presenting with acute respiratory tract illness, for human metapneumovirus.

RESULTS

A viral cause other than human metapneumovirus was determined for 279 of 687 visits for acute lower respiratory tract illness (41 percent) by 463 children in a population of 2009 infants and children prospectively seen from 1976 to 2001. There were 408 visits for lower respiratory tract illness by 321 children for which no cause was identified. Of these 321 children, specimens from 248 were available. Forty-nine of these 248 specimens (20 percent) contained human metapneumovirus RNA or viable virus. Thus, 20 percent of all previously virus-negative lower respiratory tract illnesses were attributable to human metapneumovirus, which means that 12 percent of all lower respiratory tract illnesses in this cohort were most likely due to this virus. The mean age of human metapneumovirus-infected children was 11.6 months, the male:female ratio was 1.8:1, 78 percent of illnesses occurred between December and April, and the hospitalization rate was 2 percent. The virus was associated with bronchiolitis in 59 percent of cases, pneumonia in 8 percent, croup in 18 percent, and an exacerbation of asthma in 14 percent. We also detected human metapneumovirus in 15 percent of samples from 261 patients with upper respiratory tract infection but in only 1 of 86 samples from asymptomatic children.

CONCLUSIONS

Human metapneumovirus infection is a leading cause of respiratory tract infection in the first years of life, with a spectrum of disease similar to that of respiratory syncytial virus.

Virological features and clinical manifestations associated with human metapneumovirus: a new paramyxovirus responsible for acute respiratory-tract infections in all age groups

The virological features and clinical findings associated with the new human metapneumovirus (HMPV) were examined retrospectively in Canadian patients hospitalized for various respiratory conditions since 1993. Thirty-eight previously unidentified respiratory viruses isolated from rhesus monkey kindey (LLC-MK2) cells were found to be positive for HMPV by reverse-transcription polymerase chain reaction, and those strains clustered in 2 phylogenetic groups. Children aged <5 years and elderly subjects aged >65 years represented 35.1% and 45.9% of the HMPV-infected cases, respectively. In hospitalized children, the most frequent diagnoses were pneumonitis (66.7%) and bronchiolitis (58.3%), whereas bronchitis and/or bronchospasm (60%) and pneumonitis (40%) were most commonly seen in elderly subjects. Of the 15 patients with pneumonitis, 4 (26.7%) had immunosuppressive conditions and 6 (40%) were infants aged <15 months. These findings suggest that HMPV can be associated with severe lower-respiratory-tract infections in very young children, the elderly, and immunocompromised patients.

Human metapneumovirus infections in young and elderly adults

Human metapneumovirus virus (hMPV) is a newly discovered respiratory pathogen with limited epidemiological data available. Cohorts of young and older adults were prospectively evaluated for hMPV infection during 2 winter seasons. Patients hospitalized for cardiopulmonary conditions during that period were also studied. Overall, 44 (4.5%) of 984 illnesses were associated with hMPV infection, and 9 (4.1%) of 217 asymptomatic subjects were infected. There was a significant difference in rates of hMPV illnesses between years 1 and 2 (7/452 [1.5%] vs. 37/532 [7.0%]; P<.0001). In the second year, 11% of hospitalized patients had evidence of hMPV infection. Infections occurred in all age groups but were most common among young adults. Frail elderly people with hMPV infection frequently sought medical attention. In conclusion, hMPV infection occurs in adults of all ages and may account for a significant portion of persons hospitalized with respiratory infections during some years.

Prevalence and clinical symptoms of human metapneumovirus infection in hospitalized patients

During a 17-month period, we performed retrospective analyses of the prevalence of and clinical symptoms associated with human metapneumovirus (hMPV) infection, among patients in a university hospital in The Netherlands. All available nasal-aspirate, throat-swab, sputum, and bronchoalveolar-lavage samples (N=1515) were tested for hMPV RNA by reverse-transcriptase polymerase chain reaction. hMPV RNA was detected in 7% of samples from patients with respiratory tract illnesses (RTIs) and was the second-most-detected viral pathogen in these patients during the last 2 winter seasons. hMPV was detected primarily in very young children and in immunocompromised individuals. In young children, clinical symptoms associated with hMPV infection were similar to those associated with human respiratory syncytial virus (hRSV) infection, but dyspnea, feeding difficulties, and hypoxemia were reported more frequently in hRSV-infected children. Treatment with antibiotics and corticosteroids was reported more frequently in hMPV-infected children. From these data, we conclude that hMPV is an important pathogen associated with RTI.

Antigenic and genetic variability of human metapneumoviruses

Human metapneumovirus (HMPV) is a member of the subfamily Pneumovirinae within the family Paramyxoviridae. Other members of this subfamily, respiratory syncytial virus and avian pneumovirus, can be divided into subgroups based on genetic or antigenic differences or both. For HMPV, the existence of different genetic lineages has been described on the basis of variation in a limited set of available sequences. We address the antigenic relationship between genetic lineages in virus neutralization assays. In addition, we analyzed the genetic diversity of HMPV by phylogenetic analysis of sequences obtained for part of the fusion protein (n = 84) and the complete attachment protein open reading frames (n = 35). On the basis of sequence diversity between attachment protein genes and the differences in virus neutralization titers, two HMPV serotypes were defined. Each serotype could be divided into two genetic lineages, but these did not reflect major antigenic differences.

Dual infection of infants by human metapneumovirus and human respiratory syncytial virus is strongly associated with severe bronchiolitis

The association between severe bronchiolitis and dual infection by human metapneumovirus (hMPV) and human respiratory syncytial virus (hRSV) was investigated in !2-year-old infants with bronchiolitis who were admitted to the hospital during the 2001–2002 winter season. hMPV in nasopharyngeal aspirate and/or cells and fluid collected by nonbronchoscopic bronchoalveolar lavage was detected by reverse transcriptase-polymerase chain reaction (RT-PCR). hRSV was detected in nasopharyngeal aspirate and/or cells and fluid collected by nonbronchoscopic bronchoalveolar lavage by enzyme immunoassay, tissue culture, and RT-PCR. Dual infection with hMPV and hRSV confers a 10-fold increase in relative risk (RR) of admission to a pediatric intensive-care unit for mechanical ventilation (RR, 10.99 [95% confidence interval, 5.0–24.12]; P < .001, by Fisher exact test). Dual infection by hMPV and hRSV is associated with severe bronchiolitis.

Characterization of human metapneumoviruses isolated from patients in North America

Human metapneumovirus (HMPV) was recently identified in The Netherlands and was linked to acute respiratory tract illness. In this study, 11 isolates from 10 patients with respiratory disease from Quebec, Canada, were tested by a reverse-transcriptase polymerase chain reaction based on the fusion protein gene. Identified sequences were consistent with HMPV. The patients were 2 months to 87 years of age (median age, 58 years) and presented with acute respiratory tract illness during the winter season. Sequence studies of the nucleocapsid, fusion, and polymerase genes identified 2 main lineages of HMPV and cocirculation of both lineages during the same year. These findings support a previous finding that HMPV is a human respiratory pathogen that merits further study.

Real-time reverse transcriptase PCR assay for detection of human metapneumoviruses from all known genetic lineages

The discovery of human metapneumovirus and its implications for respiratory tract disease have emphasized the need for a sensitive, specific, and rapid assay to detect this virus in a clinical setting. It recently became clear that human metapneumovirus can be grouped into at least four genetic lineages. Previously described assays for the detection of human metapneumovirus were developed by using limited sequence information and failed to detect viruses from all four genetic lineages with comparable sensitivities. Here we describe the development and evaluation of a real-time reverse transcriptase PCR assay that detects human metapneumovirus from the four known genetic lineages with equal specificities and sensitivities.

Human metapneumovirus in severe respiratory syncytial virus bronchiolitis

Reverse transcription-polymerase chain reaction was used to detect segments of the M (matrix), N (nucleoprotein), and F (fusion) genes of human metapneumovirus in bronchoalveolar fluid from 30 infants with severe respiratory syncytial virus bronchiolitis. Seventy percent of them were coinfected with metapneumovirus. Such coinfection might be a factor influencing the severity of bronchiolitis.

Human metapneumovirus as a cause of community-acquired respiratory illness

Human metapneumovirus (HMPV) is a recently identified Paramyxovirus first isolated from hospitalized children with acute respiratory tract infections (ARTI). We sought evidence of HMPV infection in patients who had visited general practitioners, had influenzalike illnesses (ILI), and had negative tests for influenza and Human respiratory syncytial virus (HRSV). As part of national virologic surveillance, sentinel general practices in England and Wales collected samples from patients of all ages with ILI during winter 2000-01. Reverse transcriptase-polymerase chain reaction (PCR) for HMPV, influenza A (H1 and H3), influenza B, and HRSV (A and B) was used to screen combined nose and throat swabs. PCR products from the HMPV-positive samples were sequenced to confirm identity and construct phylogenetic trees. Of 711 swabs submitted, 408 (57.3%) were negative for influenza and HRSV; HMPV was identified in 9 (2.2%) patients. HMPV appears to be associated with community-acquired ARTI. The extent of illness and possible complications related to this new human virus need to be clarified.

Development of three multiplex RT-PCR assays for the detection of 12 respiratory RNA viruses

Three multiplex hemi-nested RT-PCR assays were developed to detect simultaneously 12 RNA respiratory viruses: influenza viruses A, B and C, human respiratory syncytial virus (hRSV), human metapneumovirus (hMPV), parainfluenza virus types 1-4 (PIV-1, -2, -3 and -4), human coronavirus OC43 and 229E (HCoV) and rhinovirus (hRV). An internal amplification control was included in one of the RT-PCR assays. The RT-PCR multiplex 1 and the hemi-nested multiplex 1 detected 1 and 0.1 TCID50 of RSV A, respectively, and 0.01 and 0.001 TCID50 of influenza virus A/H3N2, respectively. Two hundred and three nasal aspirates from hospitalised children were retrospectively tested in comparison with two conventional methods: direct immunofluorescence assay and viral isolation technique. Almost all samples (89/91) that were positive by immunofluorescence assay and/or viral isolation technique were detected by the multiplex assay. This method also detected an additional 85 viruses and 33 co-infections. The overall sensitivity (98%), rapidity and enhanced efficiency of these multiplex hemi-nested RT-PCR assays suggest that they would be a significant improvement over conventional methods for the detection of a broad spectrum of respiratory viruses.

Epidemiology of human metapneumovirus

Since the discovery of human metapneumovirus (hMPV) in 2001, the virus has been identified worldwide. hMPV is a common respiratory pathogen, particularly in infants and young children. The virus is associated with both upper and lower respiratory tract infections and may be a trigger for asthma. At least two major genotypes of hMPV circulate during community outbreaks. Whether these genotypes represent distinct serotypes remains controversial. The major challenges faced by the medical and scientific communities are the understanding of the pathogenesis of hMPV disease and the development of a safe and effective vaccine to protect against infection and disease caused by this newly recognized respiratory virus.

Genetic diversity between human metapneumovirus subgroups

Complete consensus nucleotide sequences were determined for human metapneumovirus (HMPV) isolates CAN97-83 and CAN98-75, representing the two proposed genotypes or genetic subgroups of HMPV. The overall level of genome nucleotide sequence identity and aggregate proteome amino acid sequence identity between the two HMPV subgroups were 80 and 90%, respectively, similar to the respective values of 81 and 88% between the two antigenic subgroups of human respiratory syncytial virus (HRSV). The diversity between HMPV subgroups was greatest for the SH and G proteins (59 and 37% identity, respectively), which were even more divergent than their HRSV counterparts (72 and 55% cross-subgroup identity, respectively). It is reasonable to anticipate that the two genetic subgroups of HMPV represent antigenic subgroups approximately comparable to those of HRSV.

The role of human metapneumovirus in upper respiratory tract infections in children: a 20-year experience

BACKGROUND

The role that human metapneumovirus (hMPV) plays in the etiology of upper respiratory tract infections (URIs) in children over a period of many years has not been evaluated previously.

METHODS

By use of real-time reverse-transcriptase polymerase chain reaction, we retrospectively tested nasal wash (NW) specimens for hMPV that had been obtained from a cohort of 1532 infants and children with URIs who were prospectively followed for an average of 2.4 years during the period from 1982 to 2001. Virus genes were sequenced, and prospectively collected clinical data were analyzed.

RESULTS

There were 2710 visits for URIs for which routine cultures did not reveal a viral etiology. Archival NW specimens from 2384 of these visits were available. hMPV RNA was detected in 118 (5%) of 2384 specimens. The mean age of the children with hMPV infection was 20 months, and 78% of illnesses occurred from December through May. Acute otitis media (AOM) was detected in 50% of these children. hMPV circulated each year, but the numbers of isolates detected varied by year. Reinfections with both homologous and heterologous strains occurred. Four distinct genetic lineages were present over the 20 years of surveillance, with several different lineages circulating during some seasons.

CONCLUSIONS

hMPV was detected in a substantial number of children with URIs and concomitant AOM.

N6-methyladenosine modification enables viral RNA to escape recognition by RNA sensor RIG-I

Internal N6-methyladenosine (m6A) modification is one of the most common and abundant modifications of RNA. However, the biological roles of viral RNA m6A remain elusive. Here, using human metapneumovirus (HMPV) as a model, we demonstrate that m6A serves as a molecular marker for innate immune discrimination of self from non-self RNAs. We show that HMPV RNAs are m6A methylated and that viral m6A methylation promotes HMPV replication and gene expression. Inactivating m6A addition sites with synonymous mutations or demethylase resulted in m6A-deficient recombinant HMPVs and virion RNAs that induced increased expression of type I interferon, which was dependent on the cytoplasmic RNA sensor RIG-I, and not on melanoma differentiation-associated protein 5 (MDA5). Mechanistically, m6A-deficient virion RNA induces higher expression of RIG-I, binds more efficiently to RIG-I and facilitates the conformational change of RIG-I, leading to enhanced interferon expression. Furthermore, m6A-deficient recombinant HMPVs triggered increased interferon in vivo and were attenuated in cotton rats but retained high immunogenicity. Collectively, our results highlight that (1) viruses acquire m6A in their RNA as a means of mimicking cellular RNA to avoid detection by innate immunity and (2) viral RNA m6A can serve as a target to attenuate HMPV for vaccine purposes.

Human metapneumovirus infection in the United States: clinical manifestations associated with a newly emerging respiratory infection in children

OBJECTIVE

Respiratory tract infections are a leading cause of morbidity and mortality worldwide. Recently, a newly identified human respiratory virus, human metapneumovirus (hMPV), was reported by investigators in the Netherlands. We sought to determine whether hMPV was circulating in our community and to determine the clinical features associated with hMPV infection.

METHODS

Respiratory specimens from children who were younger than 5 years and had a negative result for respiratory syncytial virus, influenza A and B, parainfluenza viruses 1 to 3, and adenovirus by direct fluorescent antibody test were screened for hMPV by reverse transcriptase-polymerase chain reaction. Samples were collected from October 30, 2001, to February 28, 2002.

RESULTS

Of the 296 patients screened, 19 (6.4%) had evidence of hMPV infection. hMPV was identified in patients with either upper or lower respiratory tract infection or both. Clinical manifestations included wheezing, hypoxia, and abnormal findings on chest radiographs (eg, focal infiltrates, peribronchial cuffing). Nosocomial infection occurred in at least 1 patient.

CONCLUSIONS

hMPV is circulating in the United States and is associated with respiratory tract disease in patients with respiratory illnesses not caused by respiratory syncytial virus, influenza, parainfluenza viruses, and adenovirus. Additional studies are required to define the epidemiology and the extent of disease in the general population caused by hMPV.

Human metapneumovirus associated with respiratory tract infections in a 3-year study of nasal swabs from infants in Italy

The newly described human metapneumovirus (hMPV) is reported here to be more commonly associated with lower respiratory tract disease. The present study examined nasal swab specimens from 90 infants with acute respiratory tract infections in Pisa, Italy, over a period of three respiratory virus seasons. The incidence of infection varied in each of the 3 years, with the rates of positivity for hMPV being 7% in 2001 but 37 and 43% in 2000 and 2002, respectively. hMPV was noted to occur seasonally in a pattern typical of the frequency of occurrence of respiratory syncytial virus. More than one-half (14 of 23) of the infants infected with hMPV had bronchopneumonia. One-third (9 of 23) of the hMPV-infected patients were also infected with another respiratory virus, a relationship that has not previously been reported. Mixed infections did not account for a higher percentage of cases of bronchopneumonia than hMPV infection alone did. Furthermore, 7 of 17 infants whose plasma was also tested for hMPV RNA were demonstrated to have virus in both nasal swab and blood specimens. The study indicates that hMPV is seen as commonly as other respiratory viruses, may be associated with severe respiratory disease in infants, can establish mixed infections with other respiratory viruses, and has a seasonal occurrence.

A 1-year experience with human metapneumovirus in children aged <5 years

Human metapneumovirus (hMPV) is a recently discovered respiratory pathogen. We tested respiratory specimens for the presence of hMPV by reverse-transcription polymerase chain reaction. These specimens were obtained over a 1-year period from children aged <5 years and had negative results by the direct fluorescent antibody test for respiratory syncytial virus, influenza A and B, parainfluenza viruses 1-3, and adenovirus. Overall, 54 (8.1%) of 668 individuals tested positive for hMPV. During March and April of the study period, hMPV was detected in 17.6% and 25.0% of specimens tested, respectively. At least 2 distinct genotypes of hMPV circulated during the study period. Fever, tachypnea, cough, rhinorrhea, retractions of the chest wall, and wheezing were common findings. Of hMPV-positive children, 60.4% were aged <12 months. hMPV accounted for a small but significant proportion of respiratory-tract disease in infants and children.

Respiratory tract reinfections by the new human Metapneumovirus in an immunocompromised child

The human Metapneumovirus (HMPV), a new member of the Paramyxoviridae family, has been recently associated with respiratory tract infections in young children. We report the case of a young, immunocompromised child who had severe lower respiratory tract infections during two consecutive winter seasons caused by genetically distinct HMPV strains.

Viral respiratory infections in hospitalized and community control children in Alaska

Respiratory syncytial virus (RSV) in Alaska Native children from the Yukon Kuskokwim (YK) Delta is associated with a hospitalization rate five times higher than that reported for the general US child population. The role of other viral respiratory pathogens has not been studied in this population. YK Delta children <3 years of age hospitalized with respiratory infections and same aged community control children were prospectively enrolled between October 2005 and September 2007. Polymerase chain reaction detection of viruses was performed on nasopharyngeal samples. Characteristics of hospitalized and asymptomatic control children were analyzed. From October 2005 to September 2007, 440 hospitalized and 425 control children were analyzed. Respiratory viruses were detected in 90% (395) of hospitalized children: 194 (44%) rhinovirus, 131 (30%) adenovirus, 102 (23%) RSV, 77 (18%) para influenza viruses (PIV), 66 (15%) human metapneumovirus (hMPV), 23 (5%) influenza, and 25 (6%) coronavirus. Fifty-two percent (221) of control children had a virus detected, most commonly rhinovirus (33%), and adenovirus (16%). RSV, PIV, hMPV, and influenza were significantly more common in hospitalized cases than control children, but rhinovirus, adenovirus, and coronavirus were not. RSV and hMPV were associated with higher severity of illness. In this study, RSV remains the most important virus associated with respiratory hospitalization, although hMPV and PIV were also common. RSV and hMPV were associated with more severe illness. Rhinovirus and adenovirus were detected in two-thirds of hospitalized children, but their frequent detection in control children made their role in respiratory hospitalization uncertain.

An outbreak of severe respiratory tract infection due to human metapneumovirus in a long-term care facility

BACKGROUND

Human metapneumovirus (hMPV) is a newly described paramyxovirus that is mainly associated with bronchiolitis in children. We sought to describe the epidemiological, virological, and histopathological findings associated with a large outbreak of hMPV infection in a long-term care facility.

METHODS

An investigation of the outbreak was performed by public health authorities, who used standardized questionnaires to collect relevant clinical information from all residents of the facility. Nasopharyngeal samples were obtained from a subset of patients who had influenza-like illnesses for testing by viral culture and reverse-transcriptase polymerase chain reaction. Lung tissue samples from a patient whose case was fatal were available for molecular, histopathological, and immunohistochemical testing.

RESULTS

A total of 96 (27%) of 364 residents of a long-term care facility presented with respiratory or constitutional symptoms between 1 January 2006 and 15 February 2006. The attack rate in the most affected ward was 72% (31 of 43 patients), which included 4 of the 6 polymerase chain reaction-confirmed cases of hMPV infection. In contrast, viral culture results were positive for hMPV in only 2 of the 5 polymerase chain reaction-positive samples tested. The most reported diagnosis was an upper respiratory tract infection or an influenza-like illness, although 21% of residents in 1 of the 3 wards that had confirmed cases of hMPV infection had lower respiratory tract infections. The fatality rate was 50% (3 of 6 patients) among confirmed cases and 9.4% (9 of 96 patients) among patients with possible cases. A patient with a fatal case had histopathological findings that confirmed the presence of hMPV RNA and proteins in the bronchiolar epithelium of affected lobes. Phylogenetic analysis revealed the presence of 2 distinct strains of hMPV circulating simultaneously on different wards.

CONCLUSION

hMPV can be associated with important outbreaks of acute respiratory tract infection in elderly institutionalized persons.

The two major human metapneumovirus genetic lineages are highly related antigenically, and the fusion (F) protein is a major contributor to this antigenic relatedness

The growth properties and antigenic relatedness of the CAN98-75 (CAN75) and the CAN97-83 (CAN83) human metapneumovirus (HMPV) strains, which represent the two distinct HMPV genetic lineages and exhibit 5 and 63% amino acid divergence in the fusion (F) and attachment (G) proteins, respectively, were investigated in vitro and in rodents and nonhuman primates. Both strains replicated to high titers (> or =6.0 log(10)) in the upper respiratory tract of hamsters and to moderate titers (> or =3.6 log(10)) in the lower respiratory tract. The two lineages exhibited 48% antigenic relatedness based on reciprocal cross-neutralization assay with postinfection hamster sera, and infection with each strain provided a high level of resistance to reinfection with the homologous or heterologous strain. Hamsters immunized with a recombinant human parainfluenza virus type 1 expressing the fusion F protein of the CAN83 strain developed a serum antibody response that efficiently neutralized virus from both lineages and were protected from challenge with either HMPV strain. This result indicates that the HMPV F protein is a major antigenic determinant that mediates extensive cross-lineage neutralization and protection. Both HMPV strains replicated to low titers in the upper and lower respiratory tracts of rhesus macaques but induced high levels of HMPV-neutralizing antibodies in serum effective against both lineages. The level of HMPV replication in chimpanzees was moderately higher, and infected animals developed mild colds. HMPV replicated the most efficiently in the respiratory tracts of African green monkeys, and the infected animals developed a high level of HMPV serum-neutralizing antibodies (1:500 to 1:1,000) effective against both lineages. Reciprocal cross-neutralization assays in which postinfection sera from all three primate species were used indicated that CAN75 and CAN83 are 64 to 99% related antigenically. HMPV-infected chimpanzees and African green monkeys were highly protected from challenge with the heterologous HMPV strain. Taken together, the results from hamsters and nonhuman primates support the conclusion that the two HMPV genetic lineages are highly related antigenically and are not distinct antigenic subtypes or subgroups as defined by reciprocal cross-neutralization in vitro.

Human metapneumovirus: a new player among respiratory viruses

The human metapneumovirus (hMPV) is a newly described member of the Paramyxoviridae family belonging to the Metapneumovirus genus. Since its initial description in 2001, hMPV has been reported in most parts of the world and isolated from the respiratory tract of subjects from all age groups. Despite the fact that prospective and case-control studies have been limited, the epidemiology and clinical manifestations associated with hMPV have been found to be reminiscent of those of the human respiratory syncytial virus, with most severe respiratory tract infections occurring in infants, elderly subjects, and immunocompromised hosts. Additional research is needed to define the pathogenesis of this viral infection and the host's specific immune response.

Human metapneumovirus infection in the Canadian population

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.

Molecular assays for detection of human metapneumovirus

The recent description of the respiratory pathogen human metapneumovirus (hMPV) has highlighted a deficiency in current diagnostic techniques for viral agents associated with acute lower respiratory tract infections. We describe two novel approaches to the detection of viral RNA by use of reverse transcriptase PCR (RT-PCR). The PCR products were identified after capture onto a solid-phase medium by hybridization with a sequence-specific, biotinylated oligonucleotide probe. The assay was applied to the screening of 329 nasopharyngeal aspirates sampled from patients suffering from respiratory tract disease. These samples were negative for other common microbial causes of respiratory tract disease. We were able to detect hMPV sequences in 32 (9.7%) samples collected from Australian patients during 2001. To further reduce result turnaround times we designed a fluorogenic TaqMan oligoprobe and combined it with the existing primers for use on the LightCycler platform. The real-time RT-PCR proved to be highly reproducible and detected hMPV in an additional 6 out of 62 samples (9.6%) tested during the comparison of the two diagnostic approaches. We found the real-time RT-PCR to be the test of choice for future investigation of samples for hMPV due to its speed, reproducibility, specificity, and sensitivity.