My wife and I were discussing the head cold I’m battling currently, and she mentioned that I needed to be extra cautious about washing my hands and such tomorrow since we’re going out to visit friends (read: poker night). My automatic reaction was to say that it didn’t matter that much since I wasn’t contagious anymore.
When she called me on that, I realized that I was just parroting something I’d been told for as long as I can remember: once you’re showing the symptoms of a common illness, you aren’t contagious anymore. But I have no idea whether or not this is based on any actual science.
Now, I realize that it makes sense to wash your hands frequently anyway to avoid passing along harmful germs in a general sense, so please understand that that isn’t what my question about. What I want to know is, once I’ve been infected, am I:
a) most contagious to others before I show any symptoms of illness;
b) most contagious after I have full-blown symptoms;
c) equally contagious for the entire duration that the virus or bacteria invade my body; or,
d) ???
You will be most infectious when your symptoms are at their worst, which is usuallly a day or two into the symptomatic period for a cold. Coughing, sneezing and runny nose are great ways for the virus to escape your body and get to someone else.
You will have been infectious from a couple of days before symptoms appeared (incubation period), and probably remain so for three or four days.
In the case of a cold, you’re generally no longer contagious once symptoms have disappeared, but this isn’t the case for all viral illnesses.
I have no cite, but think it reasonable that your contageon potential would decline somewhat sooner than your symptoms (other than fever) would, because your symptoms are caused not by the virus but by the damage it has done. Until your body beats down the virus population, they are still causing further damage - and once your body has done that, it still has to spend some time healing the damage by replacing and absorbing the burst cells viruses leave behind.
When my brother came down with strep throat and was given antibiotics, he was told that he needed to be on the antibiotics for 24 hours before he would not be contagious anymore.