Metapneumovirus cases on the rise

A new boom in an old virus threatens vulnerable populations, experts warn.

---

Cases of the potentially dangerous respiratory infection human metapneumovirus have boomed this year, as experts urge to keep up infection control measures.

Infectious disease experts say infection control measures are key to stopping the spread of the virus that can be dangerous to vulnerable populations including young children, the elderly with comorbidities and people who are immunocompromised.

Non-existent social distancing and sporadic mask wearing have enabled the virus to spread, and there is no vaccine or treatment for hMPV either, they warn.

NSW Health data shows that there were 1168 respiratory disease notifications of hMPV in the week ending 17 September, 1008 cases in the week ending 10 September and 648 the week before that.

The virus normally causes a mild infection similar to the common cold, according to NSW Health, but young children and people with weakened immune systems can have complications such as bronchitis and pneumonia.

Infectious diseases physician Professor David Gordon said hMVP was clinically and epidemiologically similar to RSV, and the virus – along with RSV and influenza – was one of the leading causes of respiratory tract infections in children.  

“More recently (in the past 10 years or so) it has been more recognised in adults and the elderly, and as a cause of pneumonia in immunosuppressed people where it can cause quite severe disease,” said the head of microbiology and infectious diseases at Flinders University.

“There is no specific treatment other than supportive, and there are no vaccines currently available.”  

As pandemic-level infection control measures have been abandoned, respiratory illnesses such as hMPV and RSV have surged in recent months, said epidemiologist Dr Jacqueline Stephens from Flinders University.

“Mask-wearing is increasingly rare and social distancing largely non-existent as the community re-engages with the social activities and events largely missed for the past three years.”

Infectious diseases physician and microbiologist Professor Paul Griffin from the University of Queensland said hMPV was more common in children but could cause more severe disease in vulnerable people, such as the immunosuppressed and elderly people with comorbidities.

“We currently do not have any vaccine or treatment for hMPV but fortunately, most people will recover relatively rapidly without any intervention,” said the director of infectious diseases at Mater Health Services.

“Basic infection control practices, including staying home if you’re unwell, good hand hygiene, and mask-wearing work for this virus as well.

“It does seem to be on the rise, which is not the first time we’ve seen this but is a little unusual this time of year.”

Professor Griffin said aggressive covid-mitigating strategies had lowered cases of several viruses including hMPV, particularly in 2020.

“Rapid antigen tests don’t find hMPV at present but when people do get a full respiratory virus PCR panel at a laboratory our ability to find hMPV has actually improved.”

The virus was identified in 2001 but since then, no drugs or vaccines have been developed to treat or prevent hMPV infections, said early career research fellow Dr Larissa Dirr at Griffith University.

“Human metapneumovirus infections pose an important threat to the health of infants, elderly, and immunocompromised people, such as transplant patients, who are most at risk of contracting hMPV, and developing severe disease, such as pneumonia or bronchiolitis.”

Dr Dirr said global studies showed that every child under five had encountered hMPV during their life, and 10-12% of children have been hospitalised due to a hMPV infection.

“It is also a virus that is prone to causing outbreaks in nursing homes and hospitals, so identifying it early and implementing appropriate precautions is very important.

Respiratory epidemiologist Dr Nusrat Homaira from the University of NSW and Sydney Children’s Hospital said detection of viruses had increased since the covid pandemic, and seasonality and distribution patterns for common respiratory viruses had changed.

“Like any other respiratory virus, we should consider keeping our children at home if they have respiratory symptoms, maintain respiratory hygiene and practice frequent hand washing to prevent transmission of respiratory infection.”

The virus has most likely been infecting humans for decades, if not centuries, said postdoctoral research associate at the Sydney Institute for Infectious Diseases, Dr Mary Petrone.

“Because it is highly likely that most Australian adults have been infected with hMPV before, we have some level of immunity against it. This was not the case for SARS-CoV-2 because our immune systems had no previous experience with that virus when we were first infected.”

Dr Petrone said increasing infection rates in Australia was in line with epidemiological patterns in other countries such as the US, where cases of hMPV spiked in March this year, at the end of their winter.

A study in The Lancet Microbe found that concentrations of hMPV in wastewater in California also increased, she said.

“This suggests that there was a bona fide rise in hMPV cases along with other respiratory viruses. We are witnessing a similar pattern of cases here in NSW as we enter spring.”