Table 1.
Selected model variables from the baseline comparative analysis, and summary calibration data and sources.*
| Model variable | Baseline value | ||||
|---|---|---|---|---|---|
| Characteristics of screening tests† | |||||
| HPV DNA testing | |||||
| Sensitivity | 90% | ||||
| Specificity | 77% | ||||
| Visual inspection with acetic acid | |||||
| Sensitivity | 41% | ||||
| Specificity | 82% | ||||
| Characteristics of screening program‡ | |||||
| Population coverage | 70% | ||||
| Loss to follow-up (per visit) | 15% | ||||
| Characteristics of vaccination program | |||||
| Population coverage of pre-adolescent girls with at least one dose | 70% | ||||
| Attrition rate (per dose)§ | 15% | ||||
| Efficacy against HPV 16/18 (1 dose, 2 doses, 3 doses) | 30%, 90%, 100% | ||||
| Duration of vaccine protection | Lifelong | ||||
| Kenya | Mozambique | Tanzania | Uganda | Zimbabwe | |
| Costs (2005 I$) | |||||
| Visual inspection with acetic acid∥ | 1.78 | 1.55 | 1.70 | 1.63 | NA |
| Woman's time and transport (1-visit strategy; 2-visit strategy)¶ | 7.67; 15.20 | 6.59; 13.04 | 7.50; 14.92 | 7.19; 14.23 | NA |
| HPV DNA test∥ | 10.68 | 9.99 | 10.43 | 10.22 | NA |
| Woman's time and transport (1-visit strategy; 2-visit strategy)¶ | 9.36; 15.20 | 8.27; 13.04 | 8.44; 14.92 | 8.99; 14.23 | NA |
| Cryosurgery∥ | 23.78 | 20.44 | 22.56 | 21.53 | NA |
| Summary of data used for model calibration | |||||
| Prevalence of high-risk HPV among women with normal cytology, % (95% CI)** | 25 (21-30) (N=369) | 23 (17-29) (N=195) | 23 (19-28) (N=381) | ††[23 (17-29)] [N=195] | ††[23 (17-29)] [N=195] |
| Data source: | De Vuyst 2003 | Castellsague 2001 | Mayaud 2001 | [Castellsague 2001] | [Castellsague 2001] |
| Prevalence of HPV 16 in cervical cancer, % (95% CI) | 43 (37-51)‡‡ (N=204) | 50 (42-58)§§ (N=302) | 41 (32-51)§§ (N=102) | 50 (43-58)§§ (N=157) | 61 (51-71) (N=98) |
| Prevalence of HPV 18 in cervical cancer, % (95% CI)∥∥ | 17 (12-23)‡‡ (N=204) | 25 (20-30)§§ (N=302) | 31 (23-41)§§ (N=102) | 26 (20-34)§§ (N=43) | 14 (8-23) (N=98) |
| Data source: | De Vuyst 2008 | Castellsague 2008; Naucler 2004 | Bosch 1995; ter Meulen 1992 | Bosch 1995; Odida 2008 | Stanczuk 2003 |
| Cancer incidence (crude rate per 100,000 women)** | 10.18 | 32.1 | 40.6 | 16.22 | 18.62 |
| Data source (registry): | Eldoret, 1998-2000 (Cancer in Africa) | Globocan 2008 | Globocan, 2002; Dar es Salaam 1990-1991; Kilimanjaro, 1998-2000 | Kyadondo County, 1998-2002 (CI5C) | Harare (African), 1998-2002 (CI5C) |
HPV = human papillomavirus; I$ = international dollars; CI = confidence interval; CI5C: Cancer incidence in five continents; NA = not available.
Sensitivity is defined as the probability of a positive test given the presence of cervical intraepithelial neoplasia grade 2 or higher. Specificity is defined as the probability of a negative test given the presence of no lesion. Because the prevalence of high-risk HPV (and thus the probability of testing positive on HPV DNA testing) varies slightly by country, HPV DNA test sensitivity and specificity vary slightly by country; we present HPV DNA test performance from Kenya here.
For screening strategies that relied on a single visit, we assumed that women who were screen positive and eligible for cryosurgery were treated in the same day; for those not eligible for cryosurgery (e.g., those with lesions covering more than 75% of the cervix or extending to the vaginal wall), we assumed referral to a secondary facility for further diagnostic testing and treatment. For two-visit screening strategies, we assumed women were screened during the first visit and returned for a second visit to obtain results (in the case of HPV DNA testing) and, if they screened positive and were eligible, receive cryosurgery. Loss to follow-up between visits, as well as additional time and transport costs for the second visit, distinguishes the two-visit strategies from the one-visit strategies.
Of the 70% who received at least one dose, 15% received one dose, 12.75% received two doses, and 72.25% received all three doses.
Cost estimate includes direct medical costs (disposable supplies, staff time, equipment, laboratory transport, staff, facilities). For cryotherapy, cost estimate includes direct medical costs for follow-up care and complications.
Cost estimate includes woman's time and transportation (roundtrip time and transportation to a primary health clinic, waiting time at the clinic, screening procedure time).
The model was calibrated to age-specific high-risk HPV prevalence and age-specific cancer incidence, but we report overall prevalence and crude incidence rates per 100,000 women here to summarize the data. Age-specific data are presented in the Appendix.
Country-specific data unavailable. Data from Mozambique (Castellsague 2001) were used as a proxy.
Data were drawn from a frequency-matched study of HIV-positive and HIV-negative women. Here we weighted the prevalence statistics for HPV 16 and 18 in each group by the prevalence of HIV in the study population prior to matching. Further details are available in the Appendix.
Prevalence and confidence intervals were derived using fixed or random effects model to pool data from more than one available in-country study (see Appendix for details).
Because our model categorized women hierarchically according to the dominant type of infection, we counted study subjects with both HPV 16 and 18 infections as having cancer attributable to HPV 16 only. Thus the prevalence of HPV 18 in cervical cancer presented here represents women without accompanying HPV 16 infections.