Seasonal changes and COVID-19 have affected patterns in human metapneumovirus.
The COVID-19 pandemic has done more than disrupt our lives—it has altered the typical seasonal appearance of numerous infectious diseases, including influenza and respiratory syncytial virus (RSV). Another virus, well known only since 2001, is human metapneumovirus (hMPV). It also seems to have changed its seasonal pattern. I like to refer to HMPV as the evil twin of RSV. It causes acute respiratory tract infections in all ages and is one of the leading causes of bronchiolitis in infants. HMPV has been associated with nearly 20,000 hospitalizations annually in children younger than 5 years.1
Studies have shown infections with hMPV to be indistinguishable from RSV and influenza.2 hMPV is known to cause croup, pneumonia, acute exacerbations of asthma, upper respiratory infections, and otitis media. Secondary bacterial infections are similar to those seen in other viral respiratory illnesses. The typical course in a healthy child will be a mild to moderate upper respiratory infection, but for some it can lead to severe symptoms and the need for hospitalization. Preterm infants and those with underlying cardiopulmonary disease are at higher risk for complications from hMPV, just as they are with RSV or influenza. Studies have shown that nearly all children have been infected by age 5 years. Recurrent infections occur throughout life, but in a healthy individual they are usually mild or asymptomatic.2
Spread of infection
Humans are the only source of infection; spread occurs by direct or close contact with contaminated secretions. In healthy infants, viral shedding has been found to last 1 to 2 weeks but may last weeks to months in an immunocompromised patient. hMPV most commonly occurs in late winter through early spring, sometimes overlapping with RSV and influenza season.2,3 Typically, it will peak a month or so later than RSV. Unlike RSV, studies have shown hMPV to be biennial, occurring in an early and late pattern.2 But just as we have seen RSV appearing in the summer, not the typical seasonal pattern we have known, it seems hMPV has followed suit.
With the increased availability of molecular diagnostic assays, surveillance testing has highlighted outbreaks of hMPV, but testing is still not as common as it is for RSV or influenza.4 Reverse transcriptase-polymerase chain reaction (RT-PCR) assays are the method of choice. One challenge here is that hMPV is difficult to isolate in cell culture.3 hMPV often is bundled together with multiple assays for other respiratory illnesses, and because of this, the cost is increased. Unlike influenza, which has readily available office testing so that patients can be treated, testing to identify hMPV does not typically affect the outcome.
Human metapneumovirus treatment is supportive care but some individuals with more severe disease will require hospitalization. Acute respiratory infection is the leading infectious cause of pediatric death worldwide and accounts for approximately 15% of deaths in children younger than 5 years.2 This includes all respiratory viruses with hMPV playing a part. As with RSV, interferon therapy is being investigated. Antimicrobials are not indicated for the hospitalized infant with pneumonia or bronchiolitis unless evidence of a concurrent bacterial infection. Additional management is outlined in the American Academy of Pediatrics guidelines for bronchiolitis.3
Control measures such as appropriate hand washing and cough etiquette are the primary means of preventing spread. Preventive measures include limiting exposure in settings such as day care where contact to hMPV may occur.3 These preventive measures, which were followed much more stringently during the pandemic, are thought to be the reason for a decrease incidence in other infections. It is also hypothesized that during the months COVID-19 was circulating with such ferocity, other viral infections were kept at bay.
What really caused such a change in the seasonal pattern still remains unknown. We have all seen sporadic cases of hMPV before, as well as RSV, throughout the year, including summer months. But the large outbreaks we had following COVID-19 in 2021 were unusual for the time of year. In winter 2022, the typical viral infections, including hMPV, RSV, and influenza were back with a vengeance. Whether we get back on track with the typical seasonal pattern remains to be seen.
1. Edwards, Kathryn M et al. Burden of human metapneumovirus infection in young children.” New Engl J Medicine. 2013;368)7): 633-643. doi:10.1056/NEJMoa1204630
2. Haynes AK, Fowlkes AL, Schneider E, Mutuc JD, Armstrong GL, Gerber SI. Human metapneumovirus circulation in the United States, 2008 to 2014. Pediatrics. 2016;137(5):e20152927. doi:10.1542/peds.2015-2927
3. Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book 2021-2024 Report of the Committee on Infectious Diseases, 32nd edit. American Academy of Pediatrics; 2021.
4. Sojati J, Zhang Y, Williams J. Interferon-mediated responses to human metapneumovirus. Pediatrics. February 2022. Accessed May 16, 2023. https://publications.aap.org/pediatrics/article/149/1MeetingAbstractsFebruary2022/241/185986/Interferon-mediated-Response-to-Human