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Multicenter Study
. 2025 Jul 16;232(Supplement_1):S109-S120.
doi: 10.1093/infdis/jiaf111.

Multicenter Cross-sectional Study on the Epidemiology of Human Metapneumovirus in Italy, 2022-2024, With a Focus on Adults Over 50 Years of Age

Alessandro Mancon  1 , Laura Pellegrinelli  2 , Greta Romano  3 , Elisa Vian  4 , Valeria Biscaro  4 , Giulia Piccirilli  5 , Tiziana Lazzarotto  5   6 , Sara Uceda Renteria  7 , Annapaola Callegaro  7 , Elisabetta Pagani  8 , Elisa Masi  8 , Guglielmo Ferrari  3 , Cristina Galli  2 , Francesca Centrone  9 , Maria Chironna  9   10 , Claudia Tiberio  11 , Erasmo Falco  11 , Valeria Micheli  1 , Federica Novazzi  12   13 , Nicasio Mancini  12   13 , Tiziano Giacomo Allice  14 , Francesco Cerutti  14 , Elena Pomari  15 , Concetta Castilletti  15 , Eleonora Lalle  16 , Fabrizio Maggi  16 , Matteo Fracella  17 , Paolo Ravanini  18 , Giulia Faolotto  18 , Roberta Schiavo  19 , Giuliana Lo Cascio  19   20 , Carla Acciarri  21 , Stefano Menzo  21   22 , Fausto Baldanti  3   23 , Guido Antonelli  17   24 , Alessandra Pierangeli  17 , Elena Pariani  2 , Antonio Piralla  3 ; AMCLI-GLIViRe Working Group
Collaborators, Affiliations
Multicenter Study

Multicenter Cross-sectional Study on the Epidemiology of Human Metapneumovirus in Italy, 2022-2024, With a Focus on Adults Over 50 Years of Age

Alessandro Mancon et al. J Infect Dis. .

Abstract

Background: Human metapneumovirus (hMPV) infections have a significant impact on public health. However, the extent of this burden in Italy remains poorly defined due to a lack of comprehensive data. The aim of this cross-sectional multicenter study was to understand the epidemiology of hMPV in Italy, particularly in older adults.

Methods: We analyzed laboratory data from molecular respiratory viral diagnostic tests conducted at 17 centers across Italy from September 2022 to August 2024. Respiratory viruses were tested from outpatients for epidemiologic surveillance and from patients presenting to tertiary hospitals for diagnostic purpose. G gene sequencing was performed on a limited number of circulating strains.

Results: Data from 96 460 tests yielded an overall hMPV positivity rate of 3.4%; the hMPV positivity rate was 2.6% in adults aged 50 years and older, a third of whom were aged >80 years. In north-west Italy, hMPV was detected more frequently in outpatients than in hospitalized patients. The temporal distribution of cases showed seasonal peaks in February 2023 and April 2024, which exhibited some geographic variation but overlapped in the general population and in the elderly. Phylogenetic analysis suggested an even distribution of hMPV-A and -B, with a predominance of clades A2c with a 111-nucleotide duplication and B2b, and the possible extinction of previously circulating clades A2c with a 180-nucleotide duplication and B2a.

Conclusions: hMPV was shown to be a relevant respiratory pathogen in older adults, who could be more likely to have severe outcomes. These findings may inform hMPV surveillance and the development of prevention strategies.

Keywords: adults; human metapneumovirus; molecular epidemiology; phylogenetic analysis; respiratory infections.

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Conflict of interest statement

Potential conflicts of interest . All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Geographical distribution of the GLIViRe (Working Group on Respiratory Viral Infections) clinical microbiology laboratories participating in the study.
Figure 2.
Figure 2.
A, Total number of respiratory samples tested for human metapneumovirus (hMPV) and hMPV positivity rate on a biweekly basis from week 35, 2022 to week 35, 2024, in Italy. B, Number of respiratory samples from subjects aged 50 years and older tested for hMPV and hMPV positivity rate on a biweekly basis from week 35, 2022 to week 35, 2024. The calendar weeks of the study period (September to August) are plotted on the X-axis; the percentage of hMPV-positive cases is plotted on the left Y-axis and represented as differently colored areas for the 2 seasons as shown in the color legend; the total number of respiratory samples tested is plotted on the right Y-axis and represented as differently colored lines as shown in the color legend.
Figure 3.
Figure 3.
Number of respiratory samples from subjects aged 50 years and older tested for human metapneumovirus (hMPV) and hMPV positivity rate on a biweekly basis from week 35, 2022 to week 35, 2024 stratified by the 4 Italian macroareas: north-west (A), north-east (B), center (C), and south (D).
Figure 4.
Figure 4.
Phylogenetic analysis of the G gene of hMPV strains circulating in Italy. A, The phylogenetic tree of hMPV-A includes 18 GLIViRe sequences from study samples (September 2022 to August 2024), 3 GLIViRe sequences from a previous study [11], and 133 reference strains. B, The phylogenetic tree of hMPV-B includes 17 GLIViRe sequences from study samples (September 2022 to August 2024) and 91 reference strains. The hMPV-A dataset (155 sequences) was aligned using the strains NL/00/1 (GenBank accession number AF371337) and NL/00/17 (GenBank accession number FJ168779) as references for genotype A1 and A2, respectively. The hMPV-B dataset (108 sequences) was aligned using NL/99/1 (GenBank accession number AY525843) and NL/94/1 (GenBank accession number FJ168778) as reference strains for sublineages B1 and B2, respectively. The alignment tool used was MAFFT version 7.525 [16] and the visualization was performed using MEGA 11 [17]. A maximum likelihood phylogenetic tree of the dataset was constructed using IQ-TREE multicore version 2.3.3 [18] with a nucleotide substitution model identified by ModelFinder [19]. Branch robustness was assessed using the Shimodaira–Hasegawa approximate likelihood-ratio test [20] and ultrafast bootstrap approximation tests [21]. The phylogenetic tree was visualized using the ggtree package [22] and a custom R script [23]. Abbreviations: G, glycoprotein; GLIViRe, Working Group on Respiratory Viral Infections; hMPV, human metapneumovirus
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