Northern California and several states on the East Coast are experiencing a dramatic surge in human metapneumovirus. Antivirals are not yet available to fend off the illness
Por: Sunita Sohrabji / ACoM
The US is experiencing a dramatic surge in human metapneumovirus — HMPV — a little-known respiratory illness, which currently has no vaccine or antiviral treatment.
The surge first began in Northern California in mid-February, but has since spread to other parts of the country, including surges in the Northeast, according to data gathered from Waste Water Scan. Sewage surveillance is one of the primary methods for tracking numerous illnesses.
CDPH tracks surge in California
Kristine Tuzon, a spokeswoman for the California Department of Public Health confirmed the surge of HMPV cases in California, but noted that data was not readily available.
“HMPV is not a reportable disease in California, however, CDPH receives voluntary HMPV data from some clinical labs. These data show HMPV test positivity is increasing and was 8.6% positive during the week ending Feb. 28,” she told ACoM. The state also uses data from wastewater surveillance.
“Compared to the last five seasons, activity at this point in the season is higher than all prior seasons except the 2022-2023 season,” said Tuzon. HMPV typically circulates in late winter and early spring. Cases this year are highest in Northern California.
HMPV is difficult to identify because it presents with symptoms similar to other respiratory illnesses, including a cold, influenza, Covid-19, and Respiratory Syncytial Virus — RSV — said Dr. William Schaffner, professor of preventive medicine and infectious diseases at the Vanderbilt University School of Medicine.
Symptoms are similar to Covid, cold and flu
“All of these respiratory viruses are similar. They present in a very similar way because they infect our lungs, our throats, those bronchial tubes that go down to our lungs and our lungs themselves. So the symptoms that they all produce look like each other,” Schaffner told ACoM.
The illness is most acute in children and older people, who may develop severe symptoms that lead them to an emergency room.
HMPV is not tracked in the simple nasal swab that simultaneously identifies Covid, RSV, and the flu. A separate test is given — usually in the emergency room — for patients who turn up with more serious symptoms, including difficulty with breathing, a persistent high fever and dehydration.
“So even an expert, an infectious disease expert such as myself, when I take care of an individual patient, I cannot tell which virus has infected them until I do specific testing,” said Schaffner.
No antiviral treatment
Currently, no vaccine exists for HMPV. Vaccinations taken against the flu or Covid-19 will not protect against HMPV, said Schaffner. He added that no antiviral treatment currently exists.
Mild symptoms may disappear within a week, but a persistent cough may remain long after. “If your illness inflames your bronchial tubes, and it almost always does, after you get over feeling acutely ill, you can be left with a chronic cough because the inflammatory response persists for a period of time,” said Schaffner.
Cases are more severe in people with underlying conditions, such as asthma, said Schaffner. Smokers are also likely to experience more severe symptoms, he noted.
Severe infections can lead to pneumonia, he noted.
HMPV is not new. “Virtually every child that is born and raised in the US — and indeed around the world — by the time they get to age five, they will have experienced infection with human metapneumovirus. And like RSV and like influenza, you can get infected again and again and again,” said Schaffner.
Cases Double at UCSF
Dr. Peter Chin-Hong, an infectious diseases specialist at the University of California, San Francisco told ACoM he is seeing 10 cases per week over the past month at UCSF’s hospital, about double from a month ago.
“We typically don’t test for HMPV unless someone is critically ill or at least hospitalized. We test when we are trying to find out the etiology of a pneumonia, especially in the ICU where it may matter most,” he said.
At UCSF, HMPV testing is part of a multiplex PCR panel for a sick patient coming in for an undefined respiratory ailment. This panel simultaneously tests for influenza A/B, RSV, SARSCoV2, parainfluenza, rhinovirus, hMPV and other respiratory illnesses, explained Chin-Hong.
“This expands the testing strategy in the ER or urgent care where SARSCoV2/influenza A and B and RSV are checked mainly because they are more common and more actionable,” he said.
“We don’t have therapy for HMPV but we want to know if someone has it, as an explanation of serious illness so we can anticipate how someone may do,” said Chin-Hong.
Severe Symptoms
Typical symptoms of HMPV include a “cold-plus,” which includes fever and wheezing which are not normally part of a cold. “Most people will just experience cold-like symptoms, which are limited to a runny nose, sinus congestion, and ear pain,” he said.
However, severe symptoms in young children, older people, or those who are immunocompromised must be evaluated immediately in urgent care or in the ER. Severe symptoms include lethargy, trouble breathing, and worse wheezing, especially if they are negative for COVID or flu, said Chin-Hong.
Otherwise healthy people who may have a cold should take precautions such as masking or frequent washing of hands to protect those around them. “Remember that HMPV may have more grave consequences in vulnerable populations if they live with you, so protect them,” said Chin-Hong.
Pediatric infections
Dr. Manisha Newaskar, a pediatric pulmonologist at Stanford Medicine’s Children’s Health Division, told ACoM she has also seen a surge in pediatric HMPV cases. “Every week, I see at least 1 or 2 severe cases, who have needed support therapy, such as oxygen, IV fluids, or ventilators.”
She characterized severe HMPV as a life-threatening illness for children, especially those with underlying conditions such as asthma and lung disease.
Parents bring in their children who may already have pneumonia, breathing difficulties, or respiratory failure. Chronic lethargy and eating difficulties, caused by trouble when attempting to breathe, are also signs of a more severe infection, said Newaskar.
A nasal swab can identify the illness, but largely only in the ER, she noted. Testing conducted outside the ER usually has a 4-5 day turnaround, and largely becomes useless at that point because patients are undergoing treatment already for HMPV symptoms.
Antibiotics cannot treat a viral infection, and no antiviral treatment is yet available. Over the counter medications, including cough suppressants, are largely ineffective, said Newaskar. She advised instead to make certain the child is adequately hydrated and to use Tylenol for a high and persistent fever.
Sick children should stay home from school until their symptoms abate, usually within a week, said Newaskar. The pediatrician also advised frequent hand-washing and using best judgement when it comes to masking in crowded spaces.
Schaffner and Newaskar both noted that HMPV vaccines are being developed by several pharmaceutical companies, and could be on the market in as little as 5 years. Schaffner also noted the development of a combination vaccine that could protect against Covid, flu, and HMPV in a single shot.
