Respiratory Illnesses in Babies & Toddlers

Adenoviruses are a family of over 50 virus types that cause a wide range of illnesses in children, including upper and lower respiratory infections, conjunctivitis (pink eye), gastroenteritis, and croup. They account for approximately 5-10% of all respiratory infections in children. Adenovirus infections tend to be more severe and prolonged than typical colds, with high fevers lasting 5-7 days. They are extremely common in young children, especially those in daycare or group settings.

Asthma is a chronic inflammatory disease of the airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing. It affects approximately 6 million children in the United States and is the most common chronic disease of childhood. In young children (under 5), it may be called "reactive airway disease" as definitive diagnosis is difficult before this age. Asthma involves airway inflammation, bronchospasm, and mucus production triggered by various stimuli.

Bronchiolitis is a common lower respiratory tract infection in infants and young children, most often caused by RSV. It causes inflammation and congestion in the small airways (bronchioles) of the lungs, leading to wheezing and difficulty breathing. It is the most common reason for hospitalization in infants under 1 year.

Acute bronchitis is an inflammation of the bronchial tubes (large airways) in the lungs, causing a persistent cough that may produce mucus. In children, it is almost always caused by viruses and typically follows a cold or upper respiratory infection. Unlike pneumonia, bronchitis does not affect the small airways or air sacs. It is important to distinguish bronchitis from bronchiolitis (which affects infants) and asthma. Antibiotics are not indicated for acute bronchitis in otherwise healthy children.

The common cold is a viral infection of the upper respiratory tract (nose and throat). Babies get an average of 6-8 colds per year, and those in daycare may get even more. Over 200 different viruses can cause colds, with rhinoviruses being the most common. While uncomfortable, colds are rarely dangerous in healthy babies.

COVID-19 is caused by the SARS-CoV-2 virus and generally causes mild illness in most infants and young children, often resembling a common cold or mild flu. However, some children — particularly those under 1 year old or with underlying health conditions — can develop severe disease. A rare but serious complication called Multisystem Inflammatory Syndrome in Children (MIS-C) can occur 2-6 weeks after infection, causing widespread inflammation affecting the heart, lungs, kidneys, brain, and other organs. Vaccines are available for children 6 months and older.

Croup is a common childhood illness that causes swelling of the voice box (larynx) and windpipe (trachea). It produces a distinctive barking cough that sounds like a seal, along with a harsh squeaky sound when breathing in (stridor). It is most common in children aged 6 months to 3 years.

Enterovirus D68 (EV-D68) is a non-polio enterovirus that causes respiratory illness ranging from mild cold-like symptoms to severe wheezing and respiratory distress. Unlike most enteroviruses, which primarily cause gastrointestinal illness, EV-D68 primarily affects the respiratory tract. It gained national attention in 2014 during a large outbreak that hospitalized hundreds of children across the United States. EV-D68 has been linked to acute flaccid myelitis (AFM), a rare but serious neurological condition causing sudden weakness or paralysis in the limbs, similar to polio. Children with asthma or a history of wheezing are at highest risk for severe respiratory illness.

Influenza (the flu) is a contagious respiratory illness caused by influenza viruses. In babies and toddlers, it can cause more severe illness than a common cold, including high fever, body aches, and extreme fatigue. Children under 5 (especially under 2) are at higher risk for serious flu complications.

Human metapneumovirus (hMPV) is a common respiratory virus first identified in 2001 that causes illness ranging from mild colds to severe bronchiolitis and pneumonia in young children. It is closely related to RSV and causes similar clinical presentations. By age 5, virtually all children have been infected at least once. hMPV is the second or third most common cause of lower respiratory tract infection in young children after RSV. It circulates primarily in late winter and spring.

Human parainfluenza viruses (HPIVs) are a group of four related viruses (HPIV-1 through HPIV-4) that are among the most common causes of respiratory illness in infants and young children. HPIV-1 and HPIV-2 are the leading causes of croup (laryngotracheobronchitis), while HPIV-3 is a major cause of bronchiolitis and pneumonia in infants — second only to RSV. Nearly all children are infected with at least one type of parainfluenza by age 5. Despite the name, parainfluenza viruses are unrelated to influenza (flu) viruses.

Pneumonia is an infection of the lungs that causes inflammation and fluid buildup in the air sacs. In babies, it is most often caused by viruses (RSV, influenza, adenovirus) but can also be bacterial. It can range from mild to serious, especially in infants under 6 months.

Reactive airway disease (RAD) is a term used to describe wheezing episodes in young children (typically under age 5) who are too young to receive a definitive asthma diagnosis. It refers to airways that are overly sensitive and react by narrowing and producing excess mucus in response to triggers such as viral infections, cold air, smoke, or allergens. While many children with RAD outgrow their symptoms by school age, some go on to develop persistent asthma — especially those with a family history of asthma or allergies, personal history of eczema, or allergic sensitization.

RSV is a very common respiratory virus that infects nearly all children by age 2. In most babies, it causes cold-like symptoms, but in infants under 6 months and premature babies, it can cause serious lower respiratory illness including bronchiolitis and pneumonia.

Whooping cough (pertussis) is a highly contagious bacterial infection caused by Bordetella pertussis. It causes severe, uncontrollable coughing fits followed by a high-pitched "whoop" sound when breathing in. It is most dangerous in infants under 12 months who are not yet fully vaccinated, and can be life-threatening in newborns.