A runny nose, cough, sore throat, breathing problems, fever, headache, diarrhea: If you came down with these symptoms in the middle of winter, you'd probably assume it's the flu and take to your bed immediately. Think again.
Another family of viruses, known as adenoviruses, often mimic the common seasonal sickness. Though they are similar, there are differences between the two.
Adenoviruses, unlike the flu, are not seasonal and can cause illness throughout the year. And while an adenovirus vaccine exists, it's available only to military recruits.
What are the symptoms?
"Most of the time, adenoviruses produce influenza-like illness with cough and runny nose and feeling crummy, but you get better," said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University. "But they can also cause conjunctivitis and, particularly in children, diarrhea."
Pinkeye (conjunctivitis) is another symptom that can result from an adenovirus infection, according to the US Centers for Disease Control and Prevention. Other signs of illness include inflammation of the stomach and intestines (gastroenteritis), bladder infections and bronchitis. When your airways become filled with mucus, they may start to spasm, which causes coughing and shortness of breath; this is bronchitis.
Some people will develop pneumonia, an infection of the lungs, as a consequence of an adenovirus infection, Schaffner said. "Of all the cases of pneumonia that occur in adults, about 5% are actually probably caused by adenovirus."
In a worst-case scenario, adenovirus could cause neurologic symptoms, including encephalitis -- an inflammation of the brain -- and meningitis -- an inflammation of the tissues surrounding the brain.
This is very rare, says the CDC, and only infants, people with existing respiratory or cardiac disease or patients with weakened immune systems, such as those who have recently undergone chemotherapy, would be likely to develop such serious illness. In extremely unusual cases, an adenovirus infection could result in death.
That said, most adenovirus infections are mild, with symptoms usually lasting about 10 days, according to the CDC. And for most patients, home remedies and over-the-counter medicines to relieve the symptoms will be the only treatment necessary.
How do these viruses spread?
Adenoviruses are spread by coughing and sneezing, direct contact with an infected person or touching objects and surfaces, such as a door handles and light switches, where adenoviruses can live and remain infectious for long periods.
Discovered in the 1950s, adenoviruses are named after the tissue where they were first found: the adenoids, located just behind the nose. There are more than 60 specific types of adenoviruses that can cause human infections; others cause sickness exclusively in animals. Differences in types result in differences in symptoms. Some types are more likely to give you pinkeye, say, while other types might lead to gastroenteritis.
Adenovirus infections "usually occur sporadically -- here a case, there a case -- so outbreaks are pretty rare," Schaffner said. That said, Oregon has seen two deadly outbreaks in recent history. One outbreak claimed the lives of seven patients in 2007, and the second outbreak led to five deaths between October 2013 and July 2014.
From 2003 through 2016, the two most commonly reported adenovirus types in the US were types 2 and 3, though four additional types -- 1, 4, 7 and 14 -- also caused illness, according to a 2017 report from the National Center for Immunization and Respiratory Disease of the CDC. These six types accounted for 85.5% of 1,497 laboratory-confirmed specimens reported during the time period.
This small number of cases is believed to be an underrepresentation of the actual number of cases due to the fact that most people who become sick either do not go to a doctor, or their doctors do not test for this virus.
And adenoviruses are still difficult to diagnose since they're not included in a panel of tests used to identify specific viruses, according to Schaffner. He said this is changing, and for that reason, he believes the number of cases will rise.
How do I avoid getting sick?
"Avoid people who are coughing and sneezing," Schaffner said. "Also avoid people who have pinkeye."
Adenoviruses are resistant to many common disinfectant products. You need a cleaner with "virucidal" activity, such as bleach, according to Alex Valsamakis, director of Clinical Virology and Molecular Microbiology and a professor of pathology at the Johns Hopkins University School of Medicine.
Adenoviruses can "stay stable at room temperature for weeks" on unclean surfaces, said Valsamakis, who described this family of viruses as "environmentally hardy."
"Wash your hands frequently and avoid touching your face," she said. "That's kind of the easiest way to prevent inadvertently transporting something from your fingers into your nose or mouth, which is where these are going to grow."
Still, Schaffner doesn't think people need to be worried about adenoviruses. "They cause principally a whole bunch of minor troublesome infections spread by children, often from children to adults," he said.
"But they're not nearly as serious as influenza."