There are several types of viruses that could be the culprit:

1.  respiratory syncytial virus (RSV)

2. influenza

3. parainfluenza viruses

4. metapneumovirus

5.  rhinoviruses

6.  coronaviruses

7. enteroviruses

8. adenoviruses

Outside of hospitalization, respiratory virus testing isn't as common because there are no at-home tests for any of those viruses except for SARS-CoV-2.

Respiratory Syncytial Virus

RSV is a single-stranded RNA virus in the Pneumoviridae family and the Orthopneumovirus genus. It was first isolated in 1955 from chimpanzees with respiratory illness at the Walter Reed Army Institute of Research, according to a report in Nature

It's the most common cause of bronchiolitis in infants, and can be severe in older adults as well. Up to 10,000 adults die each year in the U.S. from RSV, Offit noted."RSV has this reputation as a pediatric virus, but over the last 15 years, we've accumulated data that people over 65, particularly those with underlying lung or heart disease, can be affected by RSV just as severely as influenza," Schaffner said. "And in some years the impact of RSV has been as serious as the impact of flu."In most cases, however, symptoms are usually mild and resemble the common cold. These include congestion, runny nose, sneezing, dry cough, low-grade fever, and sore throat.  

Influenza is an RNA virus in the Orthomyxoviridae family and its most common subtypes are A and B. Infection typically leads to more severe symptoms than the common cold. These include fever, aches, fatigue, cough, and sore throat. People infected with influenza are most contagious in the 3 to 4 days after the illness starts, according to the CDC.The virus can be more severe in young children and in older adults, and the U.S. typically sees some 20,000 to 25,000 influenza deaths per year, though that number can reach as high as 60,000 annually, Offit said.

Parainfluenza Viruses

These  are also single-stranded RNA viruses belonging  to the Paramyxoviridae family, and fall into two genera: 

Respirovirus and Rubulavirus, and overall there are four types (1-4) and two subtypes (4a and 4b), according to the CDC. Parainfluenza viruses are the most common culprit in cases of croup, infamous for terrifying parents with the raspy sound of stridor.By age 5, almost all children are seropositive, and people can be reinfected multiple times in their lifetime, resulting in mild illness with cold-like symptoms. Older adults and people who are immunocompromised have a higher risk of severe infection, according to the CDC.


This single-stranded RNA virus in the Paramyxoviridae family was discovered in the Netherlands in 2001, but evidence suggests its been in circulation for at least 5 decades, according to the Encyclopedia of Microbiology.Common symptoms include cough, fever, and congestion, but it can lead to more severe disease in young children, older adults, and people who are immunocompromised, according to the CDC.  

RhinovirusesRhinoviruses are the most common cause of the common cold, according to the CDC. These single-stranded RNA viruses belong to the Picornaviridae family and have three types: A, B, and C.They were first isolated in the 1950s by Winston Price, MD, at Johns Hopkins University in Baltimore, during an effort to identify the cause of the common colds


Most people infected with an enterovirus have asymptomatic infections or only mild, cold-like illness. Of the more than 100 non-polio enteroviruses, most common ones are EV-D68, EV-A71, and coxsackie virus A6 (CV-A6), according to the CDC.EV-D68 more commonly causes respiratory illness, while EV-A71 and CV-A6 can cause hand, foot, and mouth disease. While EV-D68 is usually asymptomatic or causes only mild symptoms, it can in rare cases cause acute flaccid myelitis (AFM)


These DNA viruses reside in the family Adenoviridae are frequently accompanied by small, single-stranded DNA parvoviruses known as adeno-associated viruses, that don't seem to cause any specific disease. In fact, most experimental gene therapies have switched from using adenoviruses to these adeno-associated viruses to mitigate some of the side effects.

Most adenovirus infections are asymptomatic, and when they do cause symptoms, these are mostly mild. They can also range widely in the type of disease they cause."Adenoviruses are interesting. Some are directed more at the respiratory tract, while some have more intestinal symptoms and others like to give us pink eye," Schaffner said. "That viral family is very diverse and often the major impact is quite strain-specific."