Visual inspection after acetic acid (VIA) is highly heterogeneous in primary cervical screening in Amazonian Peru

Abstract

Background: Conventional cytology (Pap) and visual inspection after the application of acetic acid (VIA) are currently used in primary screening in Peru. Studies suggest that the quality of VIA is highly variable. Over 36 000 women were screened with Pap and VIA in the TATI (Tamizaje y Tratamiento Inmediato de Lesiones Cervico-uterinas) project conducted in Amazonian Peru. Within a nested study to compare several screening techniques (C-TATI), a total of 5435 women were additionally screened with liquid-based cytology (LBC) and high-risk human papillomavirus testing (HR-HPV). We investigate the variation of positivity rates of VIA, Pap, LBC and HR-HPV in C-TATI and of VIA in the full TATI intervention.

Methods: At the screening visit, midwives collected three cervical samples for Pap, LBC and HC2 before performing VIA. The dispersion factor "D" (D = Pearson chi-square value/degrees-of-freedom) was used to measure the variability of tests results. Within C-TATI, the variability of positivity rates of VIA, Pap, LBC and HR-HPV was also graphically assessed with box- and scatter plots by midwife and month of screening. Funnel plots and smoothed scatter plots were used to correlate the variation of VIA by the number of examinations performed by each midwife over the full TATI intervention.

Results: Consistently over TATI, VIA results were highly variable, independently of the examiner, the time when the test was performed and the number of tests the examiner performed (D>6, p-values<0.001). In C-TATI, VIA results varied the most while those of HR-HPV varied the least (Ds>25, p-values<0.001 for VIA, Ds<1.6, p-values>0.05 for HR-HPV). No evidence for correlation between the number of VIAs done per midwife and the variability of VIA results was observed.

Conclusion: The lack of over-dispersion for HR-HPV detection suggests that the variable VIA results do not reflect true variation in underlying disease, but a lack of consistency in human judgement.

Figure 1. Diagram of the TATI project with the number of visual examinations performed by midwives in the pilot phase (months-3–0), during the time of the comparative study (months 1–11) and after the comparative study (months 12–33).

VIA = Visual inspection after the application of acetic acid. C-TATI = Comparative screening study (months 1–11). R-TATI = rest of the TATI intervention (months 1–33).

Figure 2. Box plots of positivity rates of VIA, HPV, LBC and Pap and of inadequate rates of LBC and Pap in C-TATI.

VIA = Visual inspection after the application of acetic acid. HPV = Human papillomavirus. LBC = Liquid-based cytology. C-TATI = Comparative screening study (months 1–11). D = Dispersion factor. ASCUS+ = Atypical squamous changes of undetermined significance or worse cytological abnormalities. Inad = Inadequate.

Figure 3. Funnel plots of the variation of positivity rates of VIA performed by midwives over 33 months of the TATI intervention.

C- TATI = Comparative screening study (months 1–11). R-TATI = rest of the TATI intervention (months 1–33). Group 1: 19 midwives who participated in C-TATI and R-TATI. Group 2: 23 midwives who did not participate in C-TATI. Positivity rates of VIA performed by midwives in Group 1 are represented by capital letters “A” to “S”. Positivity rates of VIA performed by midwives in Group 2 are represented by small letters “a” to “w”.

Figure 4. Proportion of VIA exams reported positive according to the number of VIA exams carried out by midwives who performed 500 or more VIA exams throughout the intervention.

Proportion of VIA exams reported positive by midwives in Group 1 are represented by capital letters and those of midwives in Group 2 by small letters.