A 11-month old child presents with complaints of respiratory distress. On examination there is bilateral crepitation and wheezing. Which of the following is the most likely cause?
**Core Concept**
Respiratory distress in a young child, particularly with bilateral crepitation and wheezing, suggests a lower respiratory tract infection. This condition may be caused by a viral or bacterial pathogen.
**Why the Correct Answer is Right**
Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections in infants and young children, often presenting with symptoms such as wheezing, crepitation, and respiratory distress. RSV infection can lead to bronchiolitis, characterized by inflammation and damage to the bronchioles, resulting in the production of excess mucus and subsequent wheezing. The virus primarily infects the ciliated epithelial cells lining the respiratory tract, leading to impaired mucociliary clearance and increased susceptibility to secondary bacterial infections.
**Why Each Wrong Option is Incorrect**
**Option A:** While influenza A and B viruses can cause severe respiratory illness, they are less commonly associated with bronchiolitis in infants and young children compared to RSV.
**Option B:** Adenovirus can cause a range of respiratory infections, including bronchiolitis, but it is less common than RSV in this age group.
**Option C:** Mycoplasma pneumoniae typically causes respiratory infections in older children and adults, and is not a primary cause of bronchiolitis in young infants.
**Option D:** Haemophilus influenzae type b (Hib) can cause respiratory infections, but it is more commonly associated with otitis media and meningitis in unvaccinated children.
**Clinical Pearl / High-Yield Fact**
RSV infection is a common cause of hospitalization in young children, particularly those with underlying chronic conditions or premature birth.
**Correct Answer:** C. Respiratory syncytial virus (RSV)