If I Was In Car For 4.5 Hrs With A

If I was in car for 4.5 hrs with a person who began to have a sore throat the following evening. She was then diganosed with strep the next day after that evening. How long would I possibly come down with it? My concern is that I'm supposed to be with my 48 yr. old son (who received a kidney transplant on Sept. 3) seven days after I was in car with her.