Adenovirus vs flu, parainfluenza, RSV and other respiratory viruses

Why respiratory viruses look so alike

The most common causes of acute respiratory viral infections are RSV, enterovirus, rhinovirus, adenovirus, metapneumovirus, parainfluenza viruses and seasonal coronaviruses. The illnesses they cause share the same routes of transmission, course and symptoms [1].

Clinical guidelines for children say it directly: the clinical picture of an acute respiratory viral infection hardly depends on the causative virus [2]. But different viruses prefer different parts of the airways, and this shapes their symptoms [1].

Which virus affects what

What sets adenovirus apart

• it affects not only the airways but also lymphoid tissue, the conjunctiva of the eyes and the intestines [2];
• in most respiratory viral infections, fever goes down by day 2–3 in 82% of patients, but with adenovirus and flu, high fever can last up to 5–7 days [2];
• the lymph nodes, liver and spleen may become enlarged [1];
• a cough with adenovirus and RSV can last 2 weeks or longer, up to a month [1].

Blood tests

A complete blood count sometimes hints at the cause [2]:

• leukopenia (a low white blood cell count) is typical of flu and enterovirus infections;
• RSV infection can cause lymphocytic leukocytosis, sometimes above 15 × 10⁹/L;
• with adenovirus infection, white blood cells can reach 15–20 × 10⁹/L or even higher, and C-reactive protein can be above 30 mg/L. Such results require ruling out a bacterial infection; this is a doctor's decision.

The list follows the Russian Ministry of Health clinical guidelines on acute respiratory viral infections in children [2]. Test results should be interpreted by a doctor.

Timing

The incubation period of most respiratory viral infections is 2 to 7 days [2]; for adults, guidelines give 1 to 14 days, most often 1–5 days [1]. According to CDC, parainfluenza symptoms appear 2–6 days after infection [3], and RSV symptoms 4–6 days after infection [8]. Cold symptoms usually peak within 2–3 days after infection and go away in less than a week [9].

Do you need to identify the virus

For children, usually not. A virus that is found is not always the cause of the current illness, since people can carry viruses without symptoms, and antiviral treatment options are limited, so routine testing to identify the virus is of questionable value [2]. Tests are done selectively, more often in the hospital [2].

For adults, clinical guidelines suggest rapid tests and PCR to identify the cause; a rapid swab test for flu, RSV, adenovirus and SARS-CoV-2 is done for those who seek care within 2 days of getting sick [1]. Learn more in the article on adenovirus testing.