When that happens, time is of the essence; a persistent or recurrent fever may mean the child has developed a complication such as pneumonia or a dangerous inflammatory response, and parents must seek prompt medical attention.

Parents should also be on the lookout for sepsis, a life-threatening complication caused by the body’s overwhelming attack against an infection. The condition is characterized by fever or chills, extreme pain or discomfort, clammy or sweaty skin, confusion or disorientation, shortness of breath, and a high heart rate.

“The trick with the flu is that it happens very quickly,” said Dr. Flor M. Munoz, associate professor of pediatrics and infectious diseases at Baylor College of Medicine in Houston. “You have to be really paying attention. Things can progress within 48 hours or so.”

Symptoms that call for immediate medical care are if a child’s breathing becomes labored, and he or she is taking fast, shallow breaths or feels chest pain or pressure; if the child’s lips turn blue or purple; if he or she is less responsive than usual; if the child’s skin becomes clammy; or if the child refuses to eat or drink or has diarrhea and is vomiting, raising the risk of dehydration.

In general, if a child is particularly irritable, is sleeping too much, seems confused, dizzy or not mentally alert, and not acting like his or her usual self, parents should seek medical help. Severe vomiting and seizures are also danger signs.

Concerns for Babies and Toddlers

For children under 2, parents must be vigilant about making sure their child is getting enough fluids, and watch for urine that becomes dark in color, a sign of dehydration that calls for immediate medical care. Other symptoms to watch for in infants are trouble breathing, inability to eat, significantly fewer wet diapers than normal and crying without producing tears.

Ibuprofen or acetaminophen can be used in older children, but acetaminophen is the preferred drug for fever in infants. It should be used only in appropriate doses, as instructed on the package (aspirin should never be used in children).