Which pathogen is primarily responsible for the flu?

The influenza virus is the pathogen primarily responsible for the flu. It belongs to the Orthomyxoviridae family and is an RNA virus that can cause seasonal epidemics of respiratory illness. The infection typically leads to symptoms such as fever, cough, sore throat, body aches, and fatigue. The influenza virus is highly contagious and can spread easily through droplets when an infected person coughs, sneezes, or talks. Vaccines are developed annually to combat the different strains of the virus, highlighting its importance in public health.

Other options represent different types of pathogens that cause various diseases; for example, Staphylococcus aureus is a common bacterium associated with skin infections and other types of infections, Escherichia coli is a bacterium that can cause gastrointestinal illness, and HIV is a virus that leads to AIDS. However, none of these pathogens are responsible for the flu, making the influenza virus the correct choice.