It was also before mass production of penicillin. Venereal diseases like syphilis and gonorrhea were a much bigger deal back then.
For the record, it is very hard to contract HIV from vaginal sex. (< 1/10000 per-instance chance)
http://hivinsite.ucsf.edu/insite?page=ask-05-10-11
"Two large studies in California and Europe found a per-contact risk (meaning the risk of a man becoming infected from each instance of penile-vaginal sex) of 0.0001 (1 in 10,000) and 0.0003 (1 in 3,000)"
I figure that the story took place either during the war or slightly after (late 1940s). Penicillin wasn't mass-produced and available to consumers until the 1950s.