In the depths of the Covid-19 pandemic, something strange happened: For a year or two, illnesses that used to emerge like clockwork when fall and winter arrived — flu, RSV, and the myriad viruses that cause colds — did not sicken us.
The cause now appears clear: The measures we took to avoid the new disease, including isolating and social distancing, muscled most other respiratory pathogens out of the cold-and-flu-season picture. When we started to tire of altering our lives to avoid SARS-CoV-2, which causes Covid, those other viruses returned — but at odd times and behaving in odd ways. Rhinoviruses — aka common cold viruses — made children in Hong Kong so sick they ended up in hospital.…
Data from the U.S. Centers for Disease Control and Prevention (CDC) show that a mixture of respiratory viruses are circulating right now, including common coronaviruses (other than SARS-CoV-2, which causes COVID-19), respiratory adenovirus, and parainfluenza (which is distinct from influenza). All of these viruses can cause cold-like symptoms including fever, runny nose, sore throat, and cough, so “it’s very, very hard to tell the difference between any of them clinically,” says Dr. Helen Chu, an associate professor of infectious disease at the University of Washington and a principal investigator at the Seattle Flu Alliance, which tracks respiratory disease spread. (Norovirus and rotavirus are also going around right now, but they cause gastrointestinal issues such as vomiting and diarrhea.)
“Flu and other respiratory viruses and SARS-CoV-2 just don’t get along very well together,” says virologist Richard Webby, an influenza researcher at St. Jude Children’s Research Hospital. “It’s unlikely that they will circulate widely at the same time.”
While there is some variation among panels, most multiplex PCR-based respiratory viral panels test for influenza, respiratory syncytial virus (RSV), adenovirus, parainfluenza virus, adenovirus, coronavirus (not that coronavirus–see below), rhinovirus, enterovirus, and human metapneumovirus; some also include bocavirus and offer subtyping of influenza, parainfluenza, RSV, and coronavirus. (Of note, most panels cannot distinguish between rhinovirus and enterovirus.)
The respiratory viruses that most commonly circulate in all continents as endemic or epidemic agents are influenza virus, respiratory syncytial virus, parainfluenza viruses, metapneumovirus, rhinovirus, coronaviruses, adenoviruses, and bocaviruses. Although vaccines and effective antiviral drugs are not yet available for most of these viruses, much progress has been made in the understanding of their biology and fundamental issues of host–parasite relationship. This article is a summary of the current knowledge about these viruses.
During the two-plus years of the pandemic, human behavior was transformed. With masking, social distancing and more frequent sanitizing of hands and surfaces, viral illnesses became almost obsolete.
“The two main respiratory viruses we’re currently seeing in patients are human parainfluenza virus (HPIV) and human metapneumovirus (HMPV), both of which have been around for a long time,” says Dr. Armitage. “Although the symptoms can be similar to influenza and COVID-19, these are very different viruses. And, in general, they present with milder symptoms.”
Although respiratory viruses highly impact global health, more research is needed to improve care and prognosis of severe lung viral infections. In this review, we discuss the epidemiology, diagnosis, clinical characteristics, management and prognosis of patients with severe infections due to respiratory viruses.
“We’re going to work, going to school. Kids are going to daycare. All those behavioral things that influence viral transmission are getting back to normal,” Foxman said. “In that regard I feel like those things are normalizing, and the more time that goes by that those things are normal, that will probably influence our viruses to behave as they did before.”
CDC is posting updates on the respiratory illness season here every week.