Clinical features of pneumonia are quite variable. In addition to the age of the patient, factors that affect the clinical presentation of pediatric pneumonia include the specific respiratory pathogen, the severity of the disease, and underlying illnesses. Tachypnea is the most commonly physical sign; other signs and symptoms of pneumonia include respiratory distress, rales, or decreased breath sounds. The absence of these findings in a well appearing child makes pneumonia unlikely. Neonates and young infants with pneumonia may present with a sepsis syndrome, and signs and symptoms can be nonspecific: fever or hypothermia, apnea, tachypnea, poor feeding, vomiting, diarrhea, lethargy, grunting, bradycardia, and shock. In older children, signs and symptoms of pneumonia are similar to adults and include fever, abnormal lung sounds, cough, and pleuritic chest pain. Possible associated findings may include headache, malaise, wheezing, rhinitis, conjunctivitis, pharyngitis, and rash. The clinical manifestations of bacterial and viral pneumonias overlap, making the clinical distinction problematic. Lower lobe pneumonias may cause significant abdominal pain and distention mimicking acute appendicitis.