Chances are you've never heard of human metapneumovirus. But, it's quite possible that you've been sick with this respiratory germ at some point in your life.
Discovered only 12 years ago, human metapneumovirus (HMPV) shares many symptoms with the flu. And, like the flu, most people who get it are miserable for a short time and then get better with no complications.
"It turns out that human metapneumovirus is one of the most common causes of acute respiratory infections," said study senior author Dr. John Williams, an associate professor of pediatrics at the Vanderbilt University School of Medicine in Nashville, Tenn.
"Everyone knows about flu and RSV [respiratory syncytial virus], but it's just in the last couple of years that HPMV is making it into the medical school textbooks. For otherwise healthy children and adults, it tends to be a minor illness, like a cold, but populations that are vulnerable to one of these viruses are vulnerable to all of them," said Williams, who added that this generally includes the very young, the very old, and people with underlying health problems, such as asthma or chronic heart disease.
"Now, that we've discovered this leading cause of respiratory infections in kids, it gives us a target for a vaccine," he noted.
The study was supported by a grant from the New Vaccine Surveillance Network of the U.S. Centers for Disease Control and Prevention. It was published in the Feb. 14 issue of the New England Journal of Medicine.
Human metapneumovirus was only discovered in 2001, though it was likely causing disease for many years before it was identified, according to background information in the study. And, although it's been a dozen years since the disease was discovered, it was still unclear how often people were infected, and how severe the illness could be.
To track down these answers, Williams and his Vanderbilt colleague Dr. Kathryn Edwards, along with other researchers, collected data on the virus from hospitals in three U.S. counties from 2003 through 2009.
They found the virus in 200 of 3,490 children (6 percent) hospitalized during that time period. Of 3,257 outpatient clinic visits, they found 7 percent of children had HPMV. And, of 3,001 children seen in emergency rooms, 7 percent had the virus. The researchers also tested 770 children who weren't having any symptoms, and found the virus in 1 percent.
Annually, one out of every 1,000 hospitalizations in children less than 5 years old was due to human metapneumovirus. In those less than 6 months of age, the rate of hospitalization due to HPMV was three per 1,000. In children aged 6 months to 1 year, that number was two per 1,000, according to the study.
Children hospitalized with an HPMV infection were more likely to also have pneumonia or asthma, to need oxygen therapy, and to have a longer stay in the intensive care unit. Children with asthma or who had been born prematurely were more likely to be hospitalized with HPMV. However, most children who contracted the virus were otherwise healthy, according to the study.
The researchers estimate that the annual number of outpatient visits is about 55 per 1,000 children, and the number of ER visits is likely 13 per 1,000 children. That means about 1 million outpatient visits and 263,000 emergency room visits in children under 5 years old each year are due to this virus.
Bromberg said that parents don't need to be any more concerned about this virus than they are about flu or RSV.
Study author Williams agreed and said that by age 5, almost everyone has already had this disease. Each year, its peak activity tends to be from February through April, he said. And, the symptoms are like those of the common cold: runny nose, cough, and fever. He said without testing, it's difficult to know what virus someone has, but there isn't a rapid test available for HPMV.
There's also no specific treatment for HPMV. The medications that can help ease symptoms of flu don't help with HPMV.