Amy Schumer said her son was hospitalized with a flu-like virus that's sickening kids across the US. Here are the symptoms to watch out for.

• Amy Schumer revealed in an Instagram post that her 3-year-old son, Gene, was rushed to the emergency room last week.
• She said he was admitted with RSV, a respiratory illness that can be serious for young kids.

Hours after hosting "Saturday Night Live," Amy Schumer posted on Instagram to share that her 3-year-old son, Gene, had a health emergency over the weekend.

The comedian, 41, said she missed Thursday rehearsals when her son was "rushed to the ER and admitted for RSV."

Respiratory syncytial virus (RSV) typically causes mild cold- or flu-like symptoms in adults and older kids. But for young children, babies, and elderly people, the viral infection can become more serious, requiring hospitalization.

While most cases of RSV resolve without treatment, approximately 58,000 children younger than 5 years are hospitalized with the virus each year, according to the Centers for Disease Control and Prevention.

Schumer also shared a photo on her Instagram story, where she and Gene were lying in a hospital bed together while the toddler received supplemental oxygen.

She added that her son has since returned home and is doing better.

Symptoms of RSV include runny nose, cough, and trouble breathing

Most kids will contract RSV without getting seriously unwell by the time they are 2 years old, according to the CDC.

Early symptoms of RSV include runny nose, decreased appetite, and a cough that may progress to wheezing. Fever may occur, but is not always present with RSV infections.

Young infants may only exhibit a single symptom, such as irritability, decreased activity, decreased appetite, and breathing irregularities. The CDC recommends seeing a medical provider if symptoms worsen, especially if the infant is having trouble breathing or not drinking enough fluids.

Premature infants — especially those with birth defects — and babies younger than 6 months have a higher risk of getting severely ill from RSV.

The viral infection can cause inflammation or fluid buildup in the lungs, making it the leading cause of pneumonia and bronchiolitis in children younger than 1 in the US, according to the CDC. Kids and babies with neuromuscular disorders that affect swallowing may need help clearing mucus associated with the infection.

People hospitalized with RSV may require additional oxygen, IV fluids, or intubation if breathing is severely compromised. Most cases improve with supportive care and are discharged from the hospital in a few days, according to the CDC.