Upper respiratory infection (URI) is caused by a variety of pathogens, including viruses, bacteria, fungi, and parasites. Antibiotics are not effective against viral infections, which account for the majority of URIs. Even when the pathogen is a bacterial species, antibiotics are typically prescribed in cases where the infection has progressed beyond the acute stage, meaning that the bacteria is likely to have been shed in nasal secretions.

While the duration of contagiousness of URI can vary based on the pathogen and the stage of infection, in general, it is recommended that individuals take measures to prevent the spread of the virus. These measures include:

1. Regular handwashing with soap and water for at least 20 seconds.
2. Coughing or sneezing into the crook of the elbow or a tissue.
3. Avoiding close contact with people who are sick.
4. Practicing social distancing.
5. Wearing a face mask if experiencing flu-like symptoms.

It is important to note that the duration of contagiousness of URI can be influenced by factors such as the individual's overall health and the severity of their symptoms. Individuals with a weakened immune system or a weakened respiratory system may experience more severe symptoms and be contagious for a longer period. Additionally, some people with weakened immune systems may be contagious even without exhibiting symptoms.

It is recommended that individuals with URI refrain from attending school or work for at least 24 hours after their fever subsides. It is also advised to avoid close contact with others, especially individuals with weakened immune systems, during the contagious period.

In summary, URI is typically caused by a variety of pathogens, including bacteria, viruses, fungi, and parasites. While antibiotics are not effective against viral infections, they are prescribed for bacterial infections that have progressed beyond the acute stage. The duration of contagiousness of URI can vary based on the pathogen and the stage of infection. It is recommended that individuals take measures to prevent the spread of the virus, including regular handwashing with soap and water, coughing or sneezing into the crook of the elbow or a tissue, avoiding close contact with people who are sick, and practicing social distancing. Individuals with weakened immune systems or a weakened respiratory system may experience more severe symptoms and be contagious for a longer period. It is recommended that individuals with URI refrain from attending school or work for at least 24 hours after their fever subsides, and they should avoid close contact with others, especially individuals with weakened immune systems, during the contagious period.