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Trends of acute respiratory infection, including human metapneumovirus, in the Northern Hemisphere
Situation at a glance
In many countries of the Northern Hemisphere, trends in acute respiratory infections increase at this time of year. These increases are typically caused by seasonal epidemics of respiratory pathogens such as seasonal influenza, respiratory syncytial virus (RSV), and other common respiratory viruses, including human metapneumovirus (hMPV), as well as mycoplasma pneumoniae. Many countries conduct routine surveillance for acute respiratory infections and common respiratory pathogens. Currently, in some countries in the temperate Northern hemisphere, influenza-like illness (ILI) and/or acute respiratory infection (ARI) rates have increased in recent weeks and are above baseline levels, following usual seasonal trends. Seasonal influenza activity is elevated in many countries in the Northern hemisphere. Where surveillance data is available, trends in RSV detections currently vary by region with decreases reported in most regions except in North America. Recently, there has been interest in hMPV cases in China including suggestions of hospitals being overwhelmed. hMPV is a common respiratory virus found to circulate in many countries in winter through to spring, although not all countries routinely test and publish data on trends in hMPV . While some cases can be hospitalized with bronchitis or pneumonia, most people infected with hMPV have mild upper respiratory symptoms similar to the common cold and recover after a few days. Based on data published by China, covering the period up to 29 December 2024, acute respiratory infections have increased during recent weeks and detections of seasonal influenza, rhinovirus, RSV, and hMPV, particularly in northern provinces of China have also increased. The observed increase in respiratory pathogen detections is within the range expected for this time of year during the Northern hemisphere winter. In China, influenza is the most commonly detected respiratory pathogen currently affecting people with acute respiratory infections. WHO is in contact with Chinese health officials and has not received any reports of unusual outbreak patterns. Chinese authorities report that the health care system is not overwhelmed and there have been no emergency declarations or responses triggered. WHO continues to monitor respiratory illnesses at global, regional and country levels through collaborative surveillance systems, and provides updates as needed.
Description of the situation
In many countries of the Northern Hemisphere, trends in acute respiratory infections increase at this time of year. These increases are typically caused by seasonal epidemics of respiratory pathogens such as seasonal influenza, RSV, and other common respiratory viruses, including hMPV, as well as mycoplasma pneumoniae. The co-circulation of multiple respiratory pathogens during the winter season can sometimes cause an increased burden on health care systems treating sick persons.
Currently, in some countries in the temperate Northern hemisphere, influenza-like illness (ILI) and/or acute respiratory infection (ARI) rates have increased in recent weeks and are above baseline levels, following usual seasonal trends. Influenza activity is elevated in many countries in Europe, Central America and the Caribbean, Western Africa, Middle Africa, and many countries across Asia, with the predominant seasonal influenza type and subtype varying by location, typical for this time of year, except during most of 2020 and 2021, when there was little influenza activity during the COVID-19 pandemic (Figure 1). SARS-CoV-2 activity as detected in sentinel surveillance and reported to Global Influenza Surveillance and Response System (GISRS), along with wastewater monitoring from the reporting countries, is currently low in countries in the Northern hemisphere following prolonged high level activity during summer months in the Northern hemisphere. Where surveillance data is available, trends in RSV activity are variable by region with downward trends observed in most subregions of the Americas, except in North America where RSV activity has increased, and decreases have been observed in the European region in recent weeks. Some countries conduct routine surveillance and report trends for other commonly circulating respiratory pathogens, such as hMPV, and report such information on a routine basis. Some countries in the Northern hemisphere have reported increased trends, varying by virus, in recent weeks, typical for this time of year.
There has been international interest in a potential increase of respiratory virus transmission in China, particularly hMPV, including suggestions of hospitals being overwhelmed. China has an established sentinel surveillance system for ILI and severe acute respiratory infections (SARI), including hMPV, and conducts routine virological surveillance for common respiratory pathogens with detailed reports published weekly on the China Center for Disease Control and Prevention (CDC) website.[1] Surveillance and laboratory data for hMPV is not available routinely from all countries.
According to the most recent surveillance data on acute respiratory infections shared by the China CDC with data up to 29 December 2024, there has been an upward trend of common acute respiratory infections, including those due to seasonal influenza viruses, RSV and hMPV – as expected for this time of year during the Northern Hemisphere winter. Influenza is currently the most reported cause of respiratory disease, with the highest positivity rate among all monitored pathogens for all age groups except children aged 5-14 years for whom mycoplasma pneumoniae had the highest positivity rate. SARS-CoV-2 activity remains low however with an increase in reported severe COVID-19 cases. The predominant circulating SARS-CoV-2 variant in the country is XDV and its sublineages accounting for 59.1% detection among sequenced samples. ILI activity in China’s northern and southern provinces have been increasing since late 2024, following the previous year’s trends. Current ILI activity in the southern provinces remains below that of the previous two years, while current ILI activity in the northern provinces is similar to levels seen at this time in the previous two years.
China’s reported levels of acute respiratory infections, including hMPV, are within the expected range for the winter season with no unusual outbreak patterns reported. Chinese authorities confirmed that the health care system is not overwhelmed, hospital utilization is currently lower than this time last year, and there have been no emergency declarations or responses triggered. Since the expected seasonal increase was observed, health messages have been provided to the public on how to prevent the spread of respiratory infections and reduce the impact of these diseases.