What pathogen is most likely to cause pneumonia in a child less than 1 year old?

The most likely pathogen to cause pneumonia in a child less than 1 year old is Respiratory Syncytial Virus (RSV). RSV is a common virus that primarily affects infants and young children, often leading to lower respiratory tract infections such as bronchiolitis and pneumonia. This age group is particularly susceptible because their immune systems are still developing, and RSV is known for its ability to cause severe respiratory distress in infants.

RSV typically leads to symptoms that include coughing, wheezing, and difficulty breathing, which can escalate into pneumonia. It is important to note that RSV infection is quite prevalent during the winter months, further increasing the likelihood of pneumonia in this vulnerable population during that time of year.

Other pathogens listed, while they can cause respiratory illness, are less common causes of pneumonia in infants. Influenza virus is more typically associated with pneumonia in older children and adults. Bordetella pertussis is primarily linked to whooping cough and is not the most common cause of pneumonia in infants. Staphylococcus aureus can cause pneumonia, particularly in cases of infection following viral illness, but it is less frequent as the initial causative agent in this age group compared to RSV.