A deadly virus that few people even know exists is causing misery across intensive care units and pediatric hospitals, doctors warn.
High rates of Covid, flu and even RSV during winter led to hospitals overflowing during winter during a situation dubbed a ‘tripledemic’.
But cases of human metapneumovirus (HMPV), which can cause bronchitis and pneumonia, shot up to record levels in spring, according to the Centers for Disease Control and Prevention’s respiratory virus surveillance systems.
It may partly explain why so many people tested negative for flu and Covid in recent months despite showing symptoms.
Dr John Williams, a pediatrician at the University of Pittsburgh who has spent his career researching vaccines and treatments for HMPV, said HMPV was ‘the most important virus you’ve never heard of’.
Cases of HMPV peaked this spring, according to the Centers for Disease Control and Prevention’s respiratory virus surveillance systems
Most patients who caught the virus probably did so unknowingly, as people are only tested for it in the hospital or emergency room
Dr Williams said that as well as flu and RSV, HMPV was one of viruses most likely to hospitalize people and even kill them.
This year in mid-March, 11 percent of tested cases were positive for HMPV. This is 36 percent higher than the average seasonal peak prior to the pandemic of seven percent.
Most patients who caught the virus probably did so unknowingly, as people are only tested for it in the hospital or emergency room.
Due to a lack of testing, the number who get infected or die from HMPV each year is not known, but test positivity — the swabs that are being tested — is on the rise.
And blood tests show that most children have had it by the age of five.
There are no vaccines or drugs to treat HMPV.
It causes a cough, runny nose, sore throat and fever. In serious cases, patients may struggle to breathe, or suffer bronchitis or pneumonia.
As with the flu, babies and the elderly are most at risk because their immune systems are either still developing or deteriorating.
HMPV is spread by direct or close contact with an infected person, such as a cough, shaking hands, sneezing or touching infected objects or surfaces.
One study found that it was the second most common cause of respiratory infections in kids after respiratory syncytial virus (RSV), which typically causes mild, cold-like symptoms but hits infants and older adults harder.
HMPV and RSV are in the Pneumoviridae family.
A New York study found it was as common in hospitalized older patients as RSV and the flu.
All three infections can cause deadly cases of pneumonia in seniors.
Leigh Davison, 59, came down for HMPV in early April after attending a family gathering.
Her symptoms were so bad that she could no longer talk on the phone.
She told CNN: ‘I couldn’t get out more than a couple of words. I would go into violent, violent coughing to the point where I was literally almost throwing up.’
She was sure she had Covid, but after six negative rapid tests became nervous about pneumonia instead as she is immunocompromised.
But she had a clear X-ray from a radiology clinic. She was to see her physician, who sent her to an ER room for further tests, which showed she had HMPV.
Ms Davison said: ‘I was like, “What?” Because it sounds really dire.’
The virus gave her severe bronchitis and she was admitted to the hospital for observation.
She was sick for around a month and then got better.
Of the respiratory infections she has had in her lifetime, HMPV was ‘the worst I’ve ever experienced’, she said.
HMPV was uncovered by Dutch researchers in 2001 from samples from children in the Netherlands with unexplained respiratory infections.
Some were seriously ill and needed to be on a ventilator, but were not testing positive for any pathogens.
The scientists looked at the virus’ genes are saw that it was closely related to avian metapneumovirus, which infects birds.
The new virus was named human metapneumovirus. The researchers think it hopped from birds to humans and then evolved.
Dr John Williams, a pediatrician at the University of Pittsburgh who has spent his career researching vaccines and treatments for HMPV, said HMPV was ‘the most important virus you’ve never heard of’.
A study from 2020 estimated that in children under five, there were more than 16 million HMPV infections in 2018, more than 600,000 hospitalizations and more than 16,000 deaths.
Meanwhile, Covid shot maker Moderna recently completed an early study of an mRNA vaccine against HMPV and parainfluenza.
Covid lockdowns have also meant that people’s immune systems are generally a lot weaker because of a lack of social interaction and natural exposure to pathogens.
An NIH-published study suggested the mortality rate for HMPV after 100 days was 43 percent.
Researchers estimate that 10 to 12 percent of respiratory illness in children is linked to HMPV.