What Causes Flu-Like Symptoms but Is Not the Flu?

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Causes of flu-like symptoms aside from influenza include other infections, inflammatory disorders, autoimmune conditions, cancer and recent immunizations, according to Healthgrades. Imbalances in electrolytes can also mimic the flu. Examples of infections that may produce the symptoms are bronchitis, Lyme disease, pneumonia, certain sexually transmitted infections and urinary tract infections.

Patients with chronic fatigue syndrome, rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus commonly experience symptoms characteristic of influenza, notes Healthgrades. Flu-like symptoms may consist of fever, muscle soreness, fatigue, body chills or headache. Coughing, sore throat, body aches and stiffness are other examples.

An oral temperature of 99.5 degrees Fahrenheit or above is considered a fever in children, while temperatures above 99 to 99.5 degrees signal fever in adults, explains Healthgrades. Fevers can develop into serious problems quickly in babies and toddlers and should be evaluated by a health care provider as soon as they occur. Older individuals should seek medical attention if they have flu-like symptoms for more than 48 hours or if the symptoms present in a way that is especially concerning. Flu-like symptoms that occur with seizures, confusion, trouble breathing or a stiff neck necessitate calling 911 for emergency medical services. Complications from unaddressed flu-like symptoms can include missed days of school or work, birth defects, miscarriages, dehydration, coma and organ failure.