How long is a virus contagious? I’ve heard it can only be transferred if the person affected still has a fever.
That is not a simple answer each as virus has a different route of transmission and a different incubation period, or period when it is replicating in the body but necessary causing symptoms.
Viruses can be transmitted by respiratory droplets, sexual contact, fecal-oral routes, or by fomites (viruses that are just floating through the are or resting on inanimate objects). Each virus has a differing amount of time that it can live without a host. The time of year can affect contagious rates, too.
During winter the humidity is lower allowing for viruses to live longer in the air and people tend to be more confined, giving you more opportunity to come in contact with someone with a virus. Let’s use the example of the common cold virus (for you biology majors, rhinovirus and coronaviradae). It is usually transmitted by respiratory secretions. The virus usually lives in a body for ten to fourteen days. You are contagious with this virus for two to three days prior to having symptoms. You are most contagious when your symptoms are the worst which is usually around days four to seven of infection. You continue to be contagious after your symptoms have resolved but not to the same degree.
We usually encourage people stay home when they have a fever, but only because that is when they are most contagious, not the only time they are contagious.
I run often but my family has a history of knee and leg circulation problems. Is it safe to continue running a few times a week, or should I switch to a different type of cardio?
Yes, it is safe for you to continue running. Knee problems can be, but are not necessarily, hereditary. Some can be due to weight, hip angles, and foot alignment, among other factors. Your family may have a predispostion for knee issues but this alone would not preclude you from any activity.
If you do begin to experience knee pain, it may be a simple adjustment to something more serious, but it is always better to be active than not. If running is what you enjoy then I would encourage you to stick with it.
As for leg circulation problems, running would be considered beneficial and not a risk factor for this condition. Because of gravity and the distance from the heart, blood in your legs is helped back to the heart by muscle contractions. The more frequently you contract your leg mucles, the better circulation you can have.