'ping pong' infection
A descriptor for the epidemiology of Trichomonas vaginalis infection, an STD, where person A is treated during sexual partner B's incubation period for same; B then becomes symptomatic after A has responded to antibiotics, resulting in an infection that 'bounces' back and forth from A/B to untreated B/A, in ping-pong ball-like manner; β-hemolytic streptococci may also have a 'ping-pong ball' pattern of infection
It's the idea that if one partner exposes the other to HPV and that person develops symptoms, then they can then in turn re-infect the former partner again with the same virus thus prolonging the recovery time where the immune system fights off and sequesters it and "clears" it from your system. According to Dr. Handsfield and Dr. Hook in the "Ask An Expert" section, Ping Pong Infection is thought to be a myth, or proven to be I guess (don't really know) as your body can't really get re-infected if it's got it already and also if your immune system is doing its job. It's similar to the idea that you can't get chicken pox twice.
Keep in mind that this only applies to the strain that you are sharing. Any new strain is a completely new infection.