WEST LAFAYETTE, Ind. — Having the flu is miserable. And what comes along with it is often even worse.

Flu complications are common and happen because a person’s immune system is already under attack. That makes it easier for other infections to take hold, said Libby Richards, an associate professor of nursing who specializes in public health in Purdue University’s School of Nursing.

The most common complications are pneumonia, sinus infections, ear infections and bronchitis.

“Pneumonia can occur as a secondary bacterial infection and occurs after you have had flu symptoms for several days. It can also occur as a viral infection, which develops more rapidly,” Richards said.

Pneumonia most commonly presents itself with flu-like symptoms, such as chills, fever and aches. More extreme symptoms include shortness of breath, chest pains, sweating, elevated pulse and a cough with green or bloody mucous.

Ear or sinus infections occur because the flu causes congestion and swelling of the nasal passages, throat and eustachian tubes. Symptoms for ear and sinus infections include facial pressure, drainage and ear pain.

If you experience signs of flu complications, Richards encourages seeking additional treatment, which could include antibiotics.

“Vaccination is the best way to reduce your chance of having complications from the flu,” she said. “Second to vaccination, working to maintain a healthy immune system can help fight off complications.”

The Centers for Disease Control and Prevention is reporting high activity of influenza and influenza-like illnesses across the country. In its latest report, the CDC estimates that during this season in the United States which started Oct. 1, at least 13 million cases have been diagnosed, and 39 children and 6,600 adults have died due to influenza. The CDC says flu activity is likely to remain elevated through January.