Papanicolaou smears induce partial immunity against sexually transmitted viral infections.
BACKGROUND
In a case-control study of hormonal contraceptives and invasive cervical cancer, an unexpected finding was a substantial decline in the prevalence of high-risk human papillomavirus (HPV) infection according to the lifetime number of Pap smears received. Here we assess the risk of 3 sexually transmitted viral infections -- herpes simplex virus 2 (HSV2), HPV, and human immunodeficiency virus (HIV) 1 and 2 -- in relation to the lifetime receipt of Pap smears.


METHODS
Stored sera taken from 1540 controls were tested for HSV2 and HIV; cervical scrapings were tested for HPV. Confounder-adjusted odds ratios for the lifetime receipt of Pap smears were estimated, relative to never having had a Papanicolau test.


RESULTS
For ever-receipt of a Papanicolau test, the odds ratios for HSV2 and HPV were 0.7 (95% confidence interval = 0.5-0.9) and 0.5 (0.3-0.7), respectively, and there were dose-response trends according to the lifetime number of Pap smears received (test for trend P = 0.02 and 0.04, respectively). For HSV2 the odds ratios according to last receipt declined from 0.8 for 10 or more years previously to 0.4 for <1 year previously (trend P = 0.002). For HPV the ORs were 0.4 (0.3-0.7) for last receipt 5-9 years previously and 0.5 (0.4-0.8) for less than 5 years previously; for HIV the odds ratio for last receipt less than 5 years previously was 0.4 (0.3-0.9). For HSV2 and HIV the crude odds ratio estimates were systematically lower than the adjusted estimates, and residual confounding cannot be ruled out. In particular, the true number of sexual partners may have been under-reported, and there was no information on the sexual activity of the male partners, or on other health behaviors of the women or their partners.


CONCLUSIONS
We hypothesize that Pap smears may provoke a short-term immune response against sexually transmitted viral infections.
Department of Public Health and Family Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa. samshap@mweb.co.za
Samuel
S
Shapiro
Margaret
M
Hoffman
Deborah
D
Constant
Lynn
L
Rosenberg
Henri
H
Carrara
Bruce Rider
BR
Allan
Dianne Jean
DJ
Marais
Jo-Ann Shelley
JA
Passmore
Anna-Lise
AL
Williamson
D000328:Adult; D005260:Female; D006801:Humans; D008875:Middle Aged; D065006:Papanicolaou Test; D027383:Papillomaviridae / Q000276:immunology; D015229:Sexually Transmitted Diseases, Viral / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D013019:South Africa / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014626:Vaginal Smears / Q000706:statistics & numerical data*