Background Literature documents incomplete and conflicting evidence between bacterial vaginosis and its association with cervical intraepithelial neoplasia in cervicovaginal smears (CS).

Aim To investigate if there is an association between bacterial vaginosis (BV) and squamous intraepithelial lesion (SIL) in CS.

Methods A retrospective analysis of 6902 cervicovaginal cases accrued during January 2006 -December 2009 from an opportunistic screening programme was done. The cases diagnosed as unsatisfactory (n = 239), glandular cell abnormalities (n = 9) and carcinoma (n = 12) were excluded. Thus the study was based on 6642 cases. These were reviewed to identify SIL and BV. The correlation with histology was done wherever available. A diagnosis of BV was rendered if 10 clue cells per low power field and at least 5 fields showing cocco-bacteria were detected on Pap stained smears. Statistical evaluation was carried by applying Z test to determine if BV has an association to SIL in CS.

Results Of the 6642 cases analysed, BV was present in 13% cases and absent in 87% cases. SIL was reported in 7% BV present group and 2% in the BV absent group (P < 0.001). The difference between the two proportions was highly significant. We also compared BV present in LSIL group with HSIL group. BV was present in 29% cases in LSIL group compared to 45% in HSIL group (P = 0.03). The difference between the two proportions was significant.

Conclusion The presence of BV was significantly higher in SIL group and was associated with the severity of SIL. The presence of BV should not deter a diagnosis of SIL but trigger a meticulous search for abnormal cells.