Influenza damages the respiratory cells and paves the way for bacterial superinfections, such as pneumonia. The longer you're sick with the flu, the more damage it causes and the higher the risk of bacterial complications. So it's important to call your doctor if you develop these hallmark flu symptoms especially when flu is in the community:¹²⁶

• Sudden onset of illness¹²⁷
• An illness so bad it feels like you've been "hit by a truck"¹²⁸
• A high or persistent fever (over 101°F).¹²⁹
• Cough130 or severe aches and pains, which can include headache¹³¹
• Fatigue and weakness that persists¹³²
• Chest discomfort¹³³
• Severe malaise (in addition to specific symptoms)¹³⁴

Your doctor can tell you if the symptoms you are experiencing are related to the flu.