Pyelonephritis is a  common lung infection to children age eight and below and is underweight, and common symptoms involve cough, weakness, lethargy, failure to thrive, fever, and night sweats.
Pyelonephritis is inflammation of the kidney, typically due to a bacterial infection. Symptoms most often include fever and flank tenderness. Other symptoms may include nausea, burning with urination, and frequent urination. 
