Pap smears may reduce the risk of some STDs

By David Douglas

NEW YORK (Reuters Health) - Pap smears may provoke a beneficial short-term immune response against sexually transmitted viral infections, South African researchers report.

In the journal Epidemiology, Dr. Samuel Shapiro of The University of Cape Town and colleagues note that some years ago they conducted a case-control study of hormonal contraceptives and cervical cancer and unexpectedly found a substantial decline in the prevalence of high-risk human papillomavirus (HPV) infection, according to the lifetime number of Pap smears received. Virtually all cases of cervical cancer are caused by HPV, which is sexually transmitted.

To investigate further, the researchers examined stored blood samples taken from 1,540 controls who had participated in the earlier study. These were tested for genital herpes virus and HIV, and cervical scrapings were tested for HPV.

Woman who had ever received a Pap smear had a lower likelihood of being infected with genital herpes virus and HPV. There also was a trend towards a lower risk as the number of lifetime smears increased and for more recent Pap smears.

Despite these apparent associations, the researchers note that there are many potentially confounding factors that were not accounted for, such as the sexual activity of male partners.

"I cannot stress sufficiently that at this point the findings are preliminary, tentative, and in need of independent confirmation," Shapiro told Reuters Health.

SOURCE: Epidemiology November 2007.