The evaluation and monitoring of the effectiveness of ART based on HIV-load is of great importance [11]. ART suppresses HIV-load, restores and improves immune function, thereby enhancing the quality of life [1, 12, 13]. The maintenance of the efficiency of ART requires some degree of high adherence, otherwise, it can inevitably lead to virological failure [14].
In this study, we observed a 70.0% retention rate from the 256 HIV infected adult patients recruited. This could be related to the limiting factors of a longitudinal study, such as lost to follow-up, change of contact, change of environment or even death. The 70.0% retention rate obtained was higher than that found by Dalal et al., (2015) and Alula et al., (2017) and raises concerns over poor maintenance of cohorts in longitudinal studies in Africa [15, 16]. Nevertheless, among the 30.0% lost to follow-up individuals, the majority of the patients were on the EFV regimen, more were men and the most representative age group range was 32–37 and 38–43 years.
We observed an overall significant decrease (p < 0.0001) in the mean value of HIV-load over time in both the EFV and NVP regimens (p = 0.0011 and p = 0.0055). This decrease in viral load was a result of the effectiveness of ART in preventing the replication of HIV. Our results are in accordance with the findings of Edward et al., (2015) who in their study in HIV-infected adults reported the effectiveness of ART in bringing about a dramatic decrease in viral load [17]. Similar results on the effectiveness of EFV and NVP were also obtained in a systematic review study aimed at determining the most effective NNRTIs when given in combination as part of ART [18].
We observed a significant increase (p = 0.0010) in the level of viral load < 40 copies/ml throughout the study, implying a progressive reduction in viral load at each time point. Patients on the EFV regimen at 24 weeks of treatment were better at achieving viral load < 40 copies/ml. At 48 weeks, patients on NVP had a better outcome in achieving the same viral load level. These results could be attributed to a difference in baseline HIV-load level in each regimen before ART initiation and treatment interruption during ART influencing the viral load. Hence, no constant decrease in HIV-load level. This finding is in accordance with the findings of Wu et al., (2015), in a five year longitudinal study evaluating the effectiveness of first-line ART in HIV/AIDS patients and with the findings of Meresse et al., (2013), reporting the impact of treatment interruption on virological response [10, 11].
Patients taking the EFV combination were less likely to experience virological failure (48.0 and 12.0%), compared to the NVP regimen group (76.0 and 40.0%) at 24 and 48 weeks, respectively. The overall failure rate (24.0%) at 48 weeks of ART could be due to non-adherence in both treatment regimens. Similar results obtained in a cohort study in Uganda, South Africa and in a meta-analysis study reporting patients on EFV based regimens were less likely to experience virological failure than patients based on NVP regimens [19-21]. Our results are, on the contrary, slightly higher than that found by Zoofaly et al., in 2015 in a prospective cohort study in Cameroon reporting a 16.0% virological failure rate at 12 months. The study suggests the association of incomplete adherence with incomplete suppression of viral load [22].
In Cameroon till date, there are no clear-cut guidelines for the use of administrating one of either EFV or NVP containing first-line NNRTI regimens, despite the proven efficacy of the EFV regimen compared to the NVP-based regimen. While several studies in resource-rich settings have provided evidence of increased risk of virological failure associated with the NVP based regimen, only a few studies have been done to verify this hypothesis in resource poor settings [20, 21].
In this study, we observed good and fair adherence to ART at 24 and 48 weeks. Good adherence (81.0%) was observed in patients on the EFV regimen and probably resulted in the reduction in viral load. Fair adherence (64.0%) was detected among patients on the NVP regimen and might be associated with the high treatment failure. The high adherence rate in patients on the EFV regimen compared to the NVP regimen could be attributed to the dosing frequency difference in the regimens. Patients on the EFV regimen are administered a single dose, easy to administer, compared to patients on the NVP regimen taking a twice-daily dose. The good adherence rate to EFV regimen is in accordance with the findings of a cross-sectional survey that reported adherence variations of between 71.0 and 93.0% [7]. Similar observations of a decrease in adherence rates were also obtained in other studies reporting higher adherence with the once-daily regimen, compared to the twice-daily regimen [6, 9, 23]. Our results are, however, higher than those found in a study among Kenyan patients on long-term ART that reported good adherence at 55.8%, fair adherence at 22.2% and poor adherence at 22.0% [24]. Increase in non-adherence was equally observed and closer to previous findings performed in Cameroon. The outcome showed poor adherence as a result of dosing frequency inconveniences, patients neglecting to take ART, being away from home and concerns over privacy [4, 8, 25]. Nevertheless, compared to our evaluation system, most of the previous studies evaluating adherence were either based on self report questionnaires, drug concentrations in the blood, macrocytosis measurements, visual analogue scales, pill-counts and medication event monitoring systems (MEMS) [6, 7, 9, 23, 24].
In this study, the proportion of patients with reduced viral loads were found to be more adherent to ART and consisted of patients in the age group ranging from 32 to 43 years. This could be because this population represents a more responsible set of individuals who may be more organized and motivated in improving their health and lifestyle. This result is in contrary to the findings from a study performed to analyze adherence among older HIV infected patients and in a prospective cohort study in Cameroon. They reported that older patients (> 50 years) showed higher tolerance to ART and young patients (< 36 years) showed poorer adherence [22, 26]. Furthermore, females were better adherent to ART. This could be due to the fact that women more often attend health care fascilities, compared to men. Consequently, a high proportion of women were represented in our study among those adherent to ART.
Limitations of the study include the loss to follow-up of patients, as that might have influenced the efficacy of our findings. In addition, we evaluated adherence based on pharmacy records, on the number of patients who continued treatment, and did not investigate the correlation or association between number of doses, adherence and viral outcome. Our findings add evidence to the need of improving strategies to evaluate adherence in HIV patients on ART. Large cohort studies are needed to validate these findings and evaluate the different methods used for assessing adherence to ART. It is important to investigate the various factors influencing adherence. The results from these studies can be incorporated to enhance the management of HIV infected individuals on ART.