Prevalence and type distribution of human papillomavirus in 5,000 British Columbia women--implications for vaccination.

BACKGROUND: Human papilloma virus (HPV) prevalence studies performed in different regions and population groups across Canada would inform public health decisions regarding implementation of anti-HPV vaccines. METHODS: A total of 8,700 liquid-based specimens from 8,660 women aged 13-86 from throughout British Columbia were collected. DNA was isolated from 4,980 of these samples and assessed for HPV prevalence and type distribution. HPV was detected by PCR analysis using tagged GP5+/6+ consensus primers to amplify the L1 region of HPV; typing was done by bi-directional sequencing of PCR products. RESULTS: Overall HPV prevalence was 16.8% (age adjusted 15.5%). Prevalence of high-risk HPV was 13.9, and 10.7% of samples contained HPV16. HPV prevalence was highest in the youngest group of women (<20 years). One-third of HPV positive samples contained more than one HPV type. Percentages of low-grade (LGIL) and high-grade intraepithelial lesions (HGIL) containing high-risk HPV are 52.3 and 79.4%, respectively. CONCLUSIONS: Overall HPV prevalence in this study is within the range of estimates from other studies. The prevalence of HPV16 is higher than what is found in other Canadian and international studies. HPV16 and HPV18 compose a majority of the high-risk virus in this study. Use of current HPV vaccines could considerably reduce HPV-related conditions including cervical cancer and procedures such as colposcopy.

Risk of invasive cervical cancer after Pap smears: the protective effect of multiple negatives.

OBJECTIVE: To determine the relationship between the number of initial negative Pap smears and risk of subsequent cervical cancer. DESIGN: A cohort study was conducted using data from the British Columbia Cervical Cancer Screening Program and British Columbia Cancer Registry. The analysis used a random sample (1%) of women aged 20-69 with Pap smears and all cases of invasive cervical cancer diagnosed between 1994 and 1999. Each negative screen defined the beginning of a screening interval and intervals longer than five years were truncated. The following variables were created for each interval: age at the beginning of the interval, interval length, previous cytological abnormality, previous cervical procedure and number of preceding consecutive negative screens. The relationship between these variables and risk of squamous cervical cancer was determined using survival analysis methods. RESULTS: A total of 388 cases of invasive cervical cancer (252 squamous) were included in the study from a study population of over 3.3 million Pap smears. The risk of invasive squamous cancer increased with time since the last negative screen, history of cytological abnormality and history of cervical therapeutic procedure. Risk was not significantly related to age (P=0.2) but was highest in women aged 30-49. Multiple consecutive negative pap smears were associated with reduced risk in women with a history of moderate atypia (P<0.0001), but not in women without a history (P=0.4). CONCLUSIONS: Multiple consecutive negative cytology was not associated with reduced risk of invasive cervical cancer in women with no history of cytological abnormality.