Doctors are warning of a little-known virus that is causing suffering in intensive care units and pediatric hospitals. While neocoronavirus, influenza, and respiratory syncytial virus often cause overcrowding in hospitals during the winter months, cases of human metapneumovirus (HMPV) have spiked to record levels in the spring, according to the Centers for Disease Control and Prevention's Respiratory Virus Surveillance System. This surge in cases may explain why many people have tested negative for influenza and new coronaviruses in recent months, despite showing symptoms.

HMPV can cause bronchitis and pneumonia, and is one of the most likely viruses to hospitalize or even kill a person, along with influenza and respiratory syncytial virus. Dr. John Williams, a pediatrician at the University of Pittsburgh who has been working on a vaccine and treatment for HMPV, says HMPV is "the most important virus you've never heard of." Blood tests show that most children have the disease before the age of 5, but there is no vaccine or medication for HMPV.

HMPV is spread through direct or close contact with an infected person, such as coughing, shaking hands, sneezing or touching an infected object or surface. It is the second most common cause of respiratory infections in children after respiratory syncytial virus (RSV), which usually causes mild cold-like symptoms but can have a greater impact on infants and older adults. All three infections cancause fatal cases of pneumonia in the elderly.

In mid-March of 2023, 11% of cases tested were positive for HMPV, which is 36% higher than the average seasonal peak prior to the influenza pandemic. Most patients who contract the virus probably do so unknowingly, as people are only tested in hospitals or emergency rooms. The number of people infected or dying from HMPV each year is unknown due to lack of testing, but positive tests are on the rise.

While HMPV may not be as well-known as other viruses, it is important to understand its potential impact. Infants and the elderly are particularly at risk due to their developing or deteriorating immune systems. As there is currently no vaccine or medication for HMPV, it is crucial to take preventative measures such as washing hands frequently and avoiding close contact with infected individuals or objects.