Viral upper respiratory tract infection (URTI): This is the most common cause of cough and fever in infants, often due to viruses such as rhinovirus, coronavirus, or respiratory syncytial virus (RSV). The symptoms are usually self-limiting and include runny nose, cough, and sometimes fever.

Bronchiolitis: Common in infants, especially those under 2 years old, caused by RSV and other viruses. It presents with cough, wheezing, and sometimes fever.
Pneumonia: Can be caused by bacteria (like Streptococcus pneumoniae) or viruses. Symptoms include cough, fever, and difficulty breathing.
Influenza: Especially during flu season, influenza can cause cough, fever, and other respiratory symptoms in infants.
Croup: Characterized by a barking cough and hoarseness, often due to a viral infection.

Pertussis (Whooping Cough): A highly contagious bacterial infection that can cause severe coughing fits, especially in infants who are not fully vaccinated. It's crucial to diagnose and treat promptly to prevent complications.
Bacterial pneumonia: While less common than viral causes, bacterial pneumonia can be severe and requires antibiotic treatment.
Congenital heart disease: Though not an infection, undiagnosed congenital heart disease can present with respiratory symptoms due to heart failure.
Foreign body aspiration: Can cause sudden onset of cough and respiratory distress, and is a medical emergency.

Tuberculosis (TB): Though rare in infants in many parts of the world, TB can cause chronic cough, fever, and other systemic symptoms.
Cystic fibrosis: A genetic disorder that can cause recurrent respiratory infections, among other symptoms.
Immunodeficiency: Conditions that impair the immune system can lead to recurrent or severe infections, including those causing cough and fever.
Anatomical abnormalities: Such as tracheoesophageal fistula or laryngomalacia, which can cause respiratory symptoms.