Antibiotics. Medicines that treat infections by killing bacteria; they have no effect on viruses, like the flu.
Antibiotic resistance. A condition in which bacteria adapt to an antibiotic medicine and become immune to it. This is a big concern due to prescribing antibiotics when they are not needed or effective.
Antiviral agent. Drugs that treat viral infections. Flu antivirals like oseltamivir phosphate (Tamiflu) or zanamivir (Relenza) can be used to treat the flu or to help prevent it in people at high risk. As a treatment, they work best if given within the first two days of the flu.
Bacteria. Microscopic one-celled organisms, some of which can cause illness.
Bronchitis. Inflammation of the airways leading to the lungs; it can be caused by viruses or bacteria. It can also be caused by irritants, including cigarette smoke.
Reye's syndrome. A life-threatening brain and liver disease that can follow infection with a virus, like the flu, and is most common in children. It’s often associated with taking drugs containing aspirin.
Sinusitis. Swelling of the sinuses, especially the ones around the nasal passages; it might be caused by infection with a virus or bacteria.
"Stomach flu." The informal name for gastrointestinal illnesses caused by any number of different microbes; it has no relation to actual influenza.
Vaccine. A substance, often given by injection, that helps protect against certain diseases; vaccines contain a dead or weakened version of a microbe, which spurs the immune system to recognize and destroy the living microbe during future infection.
Virus. A microscopic organism that invades living cells to reproduce; many, like influenza, cause illness. A virus is not affected by antibiotics.