I was giving a talk on infection control at a conference in Geneva a couple of days ago, and during a discussion with someone after the talk, I told them to "Live every day like you have MRSA." Not surprisingly, I got a bit of a strange look in response. I wasn't trying to say, "live your life to the fullest because you never know what will happen." Rather, I was trying to get the point across that healthcare workers in both the veterinary and human systems need to realize that at any point in time they could be carrying MRSA, along with various other harmful microorganisms.
People in patient care positions need to make the assumption that they are always a potential source of disease, and act accordingly while doing their jobs. If someone knew they were a carrier of a bug like MRSA, they'd likely do a better job with routine infection control practices such as handwashing. But, you rarely know whether you're carrying MRSA or not, and it's better to go on the assumption that you are and be diligent with your infection control measures.
The same basic concept applies to different situations, such as how people in the general population behave, and how they interact with other people and animals. In some ways, everyone should assume that they are carrying an infectious disease like influenza, and that every person or animal they encounter is carrying something infectious. (In reality, this is actually true, since everyone is carrying something potentially infectious in or on their body at any given time, it's just that most of the time it's not particularly serious or transmissible organisms).
There's a line between prudence and paranoia, and we don't want to create a population of germophobes who won't leave the house. However, we want to increase awareness so people do a better job of things like washing their hands and covering their mouths properly when coughing or sneezing. Assuming that you and everyone around you is mildly biohazardous maybe a way to do just that.