Respiratory Virus Spikes Unusually as CDC Identifies Human Metapneumovirus

A recent report from the Centers for Disease Control and Prevention (CDC) noted a rise in human metapneumovirus (HMPV).

Acute respiratory tract infections are among the most common illnesses experienced by people of all ages worldwide and are a leading cause of mortality and morbidity. This cold and flu season was no exception.

This last winter saw a surge in RSV (respiratory syncytial virus), influenza, and COVID-19 as people began masking less and interacting with people outside of their households more often. But just as the frequency of these cold and flu viruses was winding down, the CDC found a surge in HMPV.

At its peak in mid-March, nearly 11% of PCR tests were positive for the virus. Pre-pandemic, the number of positive cases for HMPV hovered around 7%. But, infectious disease specialists speculate that the more than 35% increase in cases is largely due to the lack of immunity people have to the virus.

“Most parts of the world went through a hibernation (or lock-down) for the past two years, and many of these viruses did not circulate in the population,” Dele Ogunseitan, PhD, MPH, an expert in infectious diseases and professor of population health and disease prevention at the University of California, Irvine told Health.

“We did not acquire the types of natural immunity that might have staved off infection. When people started mingling and traveling recently, these infections surged,” he explained.

HMPV is a known virus that has been around since 2001, or possibly longer. Typically, it causes mild, cold-like symptoms in healthy adults and children, but it does have the potential to become more serious.

“HMPV is similar to bird (avian) metapneumovirus,” Ogunseitan said. “But it likely spilled over from birds to humans or vise-versa more than 75 years ago. It causes lower respiratory tract infection, and is second only to RSV in terms of prevalence.”

Research shows that nearly every child will be infected with HMPV by the age of 5. But because immunity to the virus is not complete, re-infections can occur throughout adulthood.

“Most people have never heard of HMPV, but we...know that it has been circulating in humans for decades,” noted Brian Labus, PhD, MPH, REHS, an expert in infectious diseases and an assistant professor in the department of epidemiology and biostatistics at the UNLV School of Public Health.

HMPV is a common cause of illness in the colder months, but it isn’t something that people are routinely tested for, Labus added. “HMPV is something that circulates every winter with other cold and flu viruses. [But] as we have gotten back to our normal lives after COVID, we are getting back to our regular patterns of disease transmission as well.”

Labus also noted that COVID may have affected the community’s level of immunity to HMPV due to a lack of exposure for a couple of years. Now, he said, we are essentially catching back up.

HMPV typically causes cold-like symptoms including a cough, sore throat, fever, runny nose, and nasal congestion. Some people may have no symptoms at all, and others can develop a severe disease that includes wheezing, breathing difficulty, and even hypoxia (a low blood oxygen level) that requires hospitalization.

“Like other common cold viruses, HMPV spreads through the air by respiratory secretions created when sick people are coughing and sneezing,” Labus explained. “It can also spread by touching your eyes, nose, or mouth if the virus is on your hands from touching contaminated surfaces.”

For most people, an HMPV infection goes away on its own after a few days without any sort of treatment. But in some cases, HMPV infection can lead to more severe respiratory illnesses such as bronchiolitis and pneumonia, particularly in infants, young children, older adults, and people with weakened immune systems, said Mandy De Vries, RRT, RRT-NPS, a respiratory therapist and director of education at the American Association for Respiratory Care (AARC).

The incubation period for HMPV is estimated to be around four to six days, but some studies have found RNA from the virus as much as two weeks after the onset of symptoms. Most people with an HMPV infection will get better in about seven days without any sort of treatment. 

This is good news considering that there are still no Food and Drug Administration (FDA) approved antivirals or vaccines available to treat HMPV.

Generally, HMPV infections are mild, self-limiting, and nothing to worry about. But in children, older people, and those who are immunocompromised, getting this virus can lead to complications, cautioned Ogunseitan.

To further complicate matters, people also can get HMPV alongside other viruses—when this occurs, HMPV can lead to more severe complications and even death.

In fact, one study found that 46% of people with HMPV and another virus were at least 65 years old, with 60% of them becoming hospitalized. Another study found that at least 50% of those with HMPV and another virus were in a long-term care facility and went on to develop bronchitis or pneumonia, leading to 50% mortality.

Meanwhile, the peak age of hospitalization for children with HMPV is between 6 and 12 months of age. Interestingly, this timeframe is later than the peak age of hospitalization for RSV, which is around 2 to 3 months of age. These numbers are particularly concerning given that one study found that there were more than 14 million HMPV infections in kids younger than age 5 in 2018 and more than 16,000 deaths.

Currently, there is no cure or vaccine for HMPV—though Moderna just completed a clinical trial for an HMPV vaccine. But until something like that is approved, it is crucial that people take preventive measures to reduce the spread of HMPV and other respiratory viruses, De Vries warned.

“These measures include regular hand hygiene, proper respiratory etiquette (covering mouth and nose when coughing or sneezing), avoiding close contact with infected individuals, and staying home when experiencing respiratory symptoms,” she said.

If you or a loved one has been sick with what you assume is a virus for more than seven days, it is important to reach out to a healthcare provider for evaluation. Make an appointment sooner than seven days if you are over 60, have an infant, or have underlying medical conditions that put you at risk for complications. Seek immediate medical attention if you are wheezing or having trouble breathing.