Your probabilities need to be conditional on his having the bacteria
The probability of getting the bacteria from a given intercourse is 20% ex ante. But the probability of getting the bacteria from a given intercourse given that you do in fact have the bacteria now is much closer to 100%.
Additionally probabilities are useful for a population but useless for an individual.
The probability of getting the bacteria from a given intercourse is 20% ex ante. But the probability of getting the bacteria from a given intercourse given that you do in fact have the bacteria now is much closer to 100%.
Additionally probabilities are useful for a population but useless for an individual.