Molecular Characterization of Human Adenoviruses Before and After a Severe HAdV-7 Military Outbreak in Finland in 2024.

Authors

Niko Tervo, Marjaana Pitkäpaasi, Pilvi Hepo-Oja, Hanna Jarva, Anna Katz, Erika Lindh, Richard Lundell, Minna Paloniemi, Laura Savolainen, Carita Savolainen-Kopra, Niina Ikonen, Simo Nikkari

Published in

Influenza and other respiratory viruses. Volume 20. Issue 10. Pages e70329.

Abstract

In 2024, a severe outbreak caused by human adenovirus type 7d (HAdV-7) occurred in Finnish military garrisons. Molecular typing was implemented to support outbreak control. The aim of this study was to determine adenovirus types circulating in Finnish garrisons during 2013-2023 by retrospective surveillance and to review earlier findings to better understand factors contributing to the 2024 outbreak.
Adenovirus-positive respiratory samples collected through routine surveillance (2013-2023) and enhanced surveillance (2024-2025) were typed using type-specific PCR assays targeting types 3, 4, 7, 11, 14, 16, and 21. Whole-genome sequencing was performed on 11 selected samples. Index case interviews were conducted among conscripts infected with HAdV-7 in late 2023.
During 2013-2023, among 497 typed samples, HAdV-4 was most common (n = 446; 89.7%), followed by HAdV-3 (n = 25; 5%). Other types detected were HAdV-21 (n = 11; 2.2%), HAdV-7 (n = 6; 1.2%), and HAdV-11 (n = 1; 0.2%). HAdV-4 was predominant in 2013-2017 and HAdV-3 in 2018-2019. Between February 2024 and June 2025, 1692 adenovirus-positive respiratory samples were typed. The adenovirus types detected were HAdV-4 (n = 1133; 67%), HAdV-7 (n = 440; 26%), co-detection of HAdV-4 and -7 (n = 70; 4.1%), and HAdV-14 (n = 1; 0.1%). Epidemiological investigation and whole-genome sequencing data revealed that the adenovirus associated with the 2024 outbreak (HAdV-7d) was already circulating in Finnish garrisons in 2023.
The severity of the 2024 outbreak may reflect limited prior circulation of HAdV-7 in Finland. Although HAdV-7 continued to circulate among conscripts in 2025, the severity of the epidemic subsided, possibly due to effective preventative measures guided by active surveillance.

PMID:
42822784
Bibliographic data and abstract were imported from PubMed on 02 Oct 2026.

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