It's much more contagious when there is a live outbreak with symptoms. As with herpes zoster or shingles, outbreaks occur when the immune system is stressed. Being stressed, in the case of SPs, includes having too much sex, which is why I'm surprised I don't see more of it.
I'm always a little surprised at the comfort punters take from the humble condom being the key to avoidance. I heard two STD experts on the radio saying, in their opinion and in their experience, condoms are not enough stop the spread of STDs (including HIV). i.e. they don't work. I've never really known what to make of that.
I heard recently there is a very bad spread of gonorrhoea in South London currently and that very little is being done to slow it down. My advice is to make an assessment of the state f the SPs immune system (and your own) when deciding whether to lie down with them. If they look a bit grotty and wasted, they are likely to be more infectious. That's my principal method. There are plenty of other diseases that can be caught off them, such as staph infections of the skin, which get get stuck in the body for years and cause many problems even though they may be invisible when contact is made.
