To our knowledge, the present study is the first to examine the persistence and clearance rate of HPV infection in both treated and untreated Ethiopian women. HPV positive women in the baseline study were followed for one year with a six month interval. Persistent infection of HPV will lead to development of precancerous lesions and cervical cancer. Since women treated for cervical cancer and precancerous lesions are at risk of disease recurrence, monitoring of HPV infection at follow-up is crucial. The objective of the current prospective study was to determine the persistence rate and clearance rate of HPV infection at six and twelve months among women without treatment and women who received treatment.
In the present study, among women without treatment, persistence rate of 65.9% and clearance rate of 34.1% were recorded in 6 month follow up period, persistence rate of 46.3% (19/41) and clearance rate of 53.7% (22/41) were observed in 12 month follow up period. This finding is consistent with a study conducted in Zimbabwe, which found that the rates of persistence and clearance were 34.6% and 65.4%, respectively, (19). Our results also almost similar to a Ugandan study that found 31.2% of women completely clearing their infections (20).
However our finding is low compared to a Brazilian study that found 40.4% and 59.6% of women, respectively, experienced viral infection clearance or persistence(21). A Chinese study reported that, of 298 HPV-positive patients with CIN1 or normal cervical histology at baseline, 120 (40.26%) had persistent infection whereas 178 (59.74%) cleared their infection after a year (22). The observed difference might be attributed to variations in the studies' follow-up periods, sample sizes, and recruitment of women with normal and cervical squamous intraepithelial lesions (SILs).
In the current study, HPV-16 had high persistent rate of (92.31%; 12/13) among women without treatment in six- month follow up whereas its clearance rate was low (7.69%; 1/13). However at 12 month follow up, the persistence rate was 76.92%(10/13) while clearance rate was 23.08%(3/13). HPV-52 had by persistent rate of 75%(3/4) and clearance rate of 25%(1/4). HPV 18 had persistent rate of 57.14%(4/7) and clearance rate of 42.9%(3/7) at 12 month follow up period comparable with a Zimbabwean study which indicated HPV-16 was the most persistent type (53.8%), HPV-52 was the second most persistent type (19).
In this study, among women who were treated, persistence rate of 45.8% (22/48) and clearance rate of 54.2% (26/48) were recorded in 6 month follow up period., persistence rate of 33.3% (16/48) and clearance rate of 66.7% (32/48) were observed in 12 months, highly consistent with a Korean study indicated that following cold knife conization or loop electrosurgical excision treatment, fifty-eight patients (33.7%) had HPV infection (23). This result is also consistent with findings from other Korean studies that indicate from 398 patients, 28 (30.2%) had persistence after conization or Loop electrosurgical excision procedure (LEEP)(24), and 48 (30%) had persistent HR HPV infections and 112 (70.7%) had HPV cleared following therapy (25). However, this result is greater than that of an Italian study that found 96 individuals (23.5%) continued to have at least one genotype following therapy (26).
In the present study, HPV-18 had the highest persistent rate 44.44%(4/9) among treated women in 12 month follow up and its clearance rate was 55.56%(5/9), followed by other high risk HPVs, HPV-16 and HPV58 with persistent rate of 44.44%(4/9), 40.74%(11/27), 30%(3/10) and clearance rate of 55.56%(5/9), 59.26%(16/27), and 70%(7/10), similar with a Turkish study which indicated HPV-18 was cleared in almost all (95.8%) cases, followed by HPV 16 (69.9%) and other HR HPV types (65.6%) (7). However other studies found that the persistent infection rate for HPV-16 was higher than that of other HPV strains(27, 28, 23).
In our study, the persistent rate had decreased from six month to twelve month in both women who were not treated (from 65.9–46.34%) and women who were treated (from 45.83–33.33%). This result is supported by a systematic review by Hoffman et al. (29) which reported that median HPV persistence tended to decline over time: 27% at three-month, 21% at six-month and 10% at 24 -month after treatment. Additionally, they stated that a variety of factors, including the patient's age, the type of HPV, the method of detection, the course of treatment, and the minimum interval between HPV post-treatment tests, affected the persistence of post-treatment HPV. The result of the current study indicted there is a need to follow HPV positive women for the persistent infection and development of cervical abnormalities or recurrence of cervical neoplasia, which is supported by a study conducted in the United States that found women with persistent HPV infection had a higher risk of developing abnormalities in their epithelial cells (30).