During an epidemic, 60–70% of patients with a clear influenza-like illness actually have influenza.Samples are respiratory samples, usually collected by a physician, nurse, or assistant, and sent to a hospital laboratory for preliminary testing. There are several methods of collecting a respiratory sample, depending on requirements of the laboratory that will test the sample. A sample may be obtained from around the nose simply by wiping with a dry cotton swab. Other causes
Infectious diseases causing ILI include respiratory syncytial virus, malaria, acute HIV/AIDS infection, herpes, hepatitis C, Lyme disease, rabies, myocarditis, Q fever, dengue fever, poliomyelitis, pneumonia, measles, SARS, COVID-19, and many others. Pharmaceutical drugs that may cause ILI include many biologics such as interferons and monoclonal antibodies. Chemotherapeutic agents also commonly cause flu-like symptoms. Other drugs associated with a flu-like syndrome include bisphosphonates, caspofungin, and levamisole. A flu-like syndrome can also be caused by an influenza vaccine or other vaccines, and by opioid withdrawal in physically dependent individuals. Diagnosis
Influenza-like illness is a nonspecific respiratory illness characterized by fever, fatigue, cough, and other symptoms that stop within a few days. Most cases of ILI are caused not by influenza but by other viruses (e.g., rhinoviruses, coronaviruses, human respiratory syncytial virus, adenoviruses, and human parainfluenza viruses). Less common causes of ILI include bacteria such as Legionella, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Streptococcus pneumoniae. Influenza, RSV, and certain bacterial infections are particularly important causes of ILI because these infections can lead to serious complications requiring hospitalization.
In horses
ILI occurs in some horses after intramuscular injection of vaccines. For these horses, light exercise speeds resolution of the ILI. Non-steroidal anti-inflammatory drugs (NSAIDs) may be given with the vaccine. See also
Attack rate
Disease surveillance


== References ==