Strengthening HIV surveillance in the antiretroviral therapy era: rationale and design of a longitudinal study to monitor HIV prevalence and incidence in the uMgungundlovu District, KwaZulu-Natal, South Africa.

BACKGROUND: South Africa has over 6,000,000 HIV infected individuals and the province of KwaZulu-Natal (KZN) is the most severely affected. As public health initiatives to better control the HIV epidemic are implemented, timely, detailed and robust surveillance data are needed to monitor, evaluate and inform the programmatic interventions and policies over time. We describe the rationale and design of the HIV Incidence Provincial Surveillance System (HIPSS) to monitor HIV prevalence and incidence. METHODS/DESIGN: The household-based survey will include a sample of men and women from two sub-districts of the uMgungundlovu municipality (Vulindlela and the Greater Edendale) of KZN, South Africa. The study is designed as two sequential cross-sectional surveys of 10,000 randomly selected individuals aged 15-49 years to be conducted one year apart. From the cross sectional surveys, two sequential cohorts of HIV negative individuals aged 15-35 years will be followed-up one year later to measure the primary outcome of HIV incidence. Secondary outcomes include the laboratory measurements for pulmonary tuberculosis, sexually transmitted infections and evaluating tests for estimating population-level HIV incidence. Antiretroviral therapy (ART) access, HIV-1 RNA viral load, and CD4 cell counts in HIV positive individuals will assess the effectiveness of the HIV treatment cascade. Household and individual-level socio-demographic characteristics, exposure to HIV programmatic interventions and risk behaviours will be assessed as predictors of HIV incidence. The incidence rate ratio of the two cohorts will be calculated to quantify the change in HIV incidence between consecutive samples. In anticipation of better availability of population-level HIV prevention and treatment programmes leading to decreases in HIV incidence, the sample size provides 84% power to detect a reduction of 30% in the HIV incidence rate between surveys. DISCUSSION: The results from HIPSS will provide critical data regarding HIV prevalence and incidence in this community and will establish whether HIV prevention and treatment efforts in a "real world", non-trial setting have an impact on HIV incidence at a population level. Importantly, the study design and methods will inform future methods for HIV surveillance.

Trends in HIV Prevalence in Pregnant Women in Rural South Africa.

BACKGROUND: Despite substantial progress in the delivery of HIV prevention programs, some communities continue to experience high rates of HIV infection. We report on temporal trends in HIV prevalence in pregnant women in a community in rural KwaZulu-Natal in South Africa. METHODS: Annual, anonymous cross-sectional HIV sero-prevalence surveys were conducted between 2001 and 2013 among first visit prenatal clinic attendees. The time periods 2001 to 2003 were defined as pre-antiretroviral therapy (ART), 2004 to 2008 as early ART, and 2009 to 2013 as contemporary ART roll-out, to correspond with the substantial scale-up of ART program. RESULTS: Overall, HIV prevalence rose from 35.3% [95% confidence interval (CI): 32.3 to 38.3] pre-ART (2001-2003) to 39.0% (95% CI: 36.8 to 41.1) in the early ART (2004-2008) to 39.3% (95% CI: 37.2 to 41.4) in the contemporary ART (2009-2013) roll-out periods. In teenage women (<20 years), HIV prevalence declined from 22.5% (95% CI: 17.5 to 27.5) to 20.7% (95% CI: 17.5 to 23.8) and to 17.2% (95% CI: 14.3 to 20.2) over the similar ART roll-out periods (P = 0.046). Prevalence increased significantly in women 30 years and older (P < 0.001) over the same time period largely because of survival after ART scale up. Teenage girls with male partners of age 20-24 and ≥ 25 years had a 1.7-fold (95% CI: 1.3-2.4; P = 0.001) and 3-fold (95% CI: 2.1 to 4.3; P < 0.001) higher HIV prevalence respectively. CONCLUSIONS: Notwithstanding the encouraging decline in teenagers, the ongoing high HIV prevalence in pregnant women in this rural community, despite prevention and treatment programs, is deeply concerning. Targeted interventions for teenagers, especially for those in age-disparate relationships, are needed to impact this HIV epidemic trajectory.

HIV-positive status disclosure in patients in care in rural South Africa: implications for scaling up treatment and prevention interventions.

A nuanced understanding of HIV-positive status disclosure is urgently needed to inform the implementation of prevention interventions, including TasP and PrEP. To provide such understanding for the high HIV-burden setting of rural KwaZulu-Natal, we conducted a prospective cohort study to characterize determinants and trends in HIV-positive status disclosure. 687 consenting HIV-positive individuals (73.2 % female; 60.3 % ART initiated) were enrolled. Reports of any incidence of disclosure to either a family member or sexual partner at enrollment and follow-up visits (median 4.4 months post-enrolment) were common (91.0 %); however, reports of disclosure specifically to sexual partners were relatively rare (34.1 %), especially in women (29.8 %). Participants not engaged in a stable partnerships, not ART-imitated, and/or who had disclosed to their family were at risk of non-disclosure to sexual partners. These data highlight both an urgent need to empower HIV-positive individuals, and the significant barriers to targeting sero-discordant couples for HIV prevention in this setting.

Assessing the implementation effectiveness and safety of 1% tenofovir gel provision through family planning services in KwaZulu-Natal, South Africa: study protocol for an open-label randomized controlled trial.

BACKGROUND: The Centre for the AIDS Programme of Research in South Africa (CAPRISA) 004 trial demonstrated a 39% reduction in HIV infection, with a 54% HIV reduction in women who used tenofovir gel consistently. A confirmatory trial is expected to report results in early 2015. In the interim, we have a unique window of opportunity to prepare for and devise effective strategies for the future policy and programmatic scale-up of tenofovir gel provision. One approach is to integrate tenofovir gel provision into family planning (FP) services. The CAPRISA 008 implementation trial provides an opportunity to provide post-trial access to tenofovir gel while generating empiric evidence to assess whether integrating tenofovir gel provision into routine FP services can achieve similar levels of adherence as the CAPRISA 004 trial. METHODS/DESIGN: This is a two-arm, open-label, randomized controlled non-inferiority trial. A maximum of 700 sexually active, HIV-uninfected women aged 18 years and older who previously participated in an antiretroviral prevention study will be enrolled from an urban and rural site in KwaZulu-Natal, South Africa. The anticipated study duration is 30 months, with active accrual requiring approximately 12 months (following which an open cohort will be maintained) and follow-up continuing for approximately 18 months. At each of the two sites, eligible participants will be randomly assigned to receive tenofovir gel through either FP services (intervention arm) or through the CAPRISA research clinics (control arm). As part of the study intervention, a quality improvement approach will be used to assist the FP services to expand their current services to include tenofovir gel provision. DISCUSSION: This protocol aims to address an important implementation question on whether FP services are able to effectively incorporate tenofovir gel provision for this at-risk group of women in South Africa. Provision of tenofovir gel to the women from the CAPRISA 004 trial meets the ethical obligation for post-trial access, and helps identify a potential avenue for future scale-up of microbicides within the public health system of South Africa. TRIAL REGISTRATION: This trial was registered with the South Africa Department of Health (reference: DOH-27-0812-4129) and ClinicalTrials.gov (reference: NCT01691768) on 05 July 2012.

Meeting the sexual and reproductive health needs of high-school students in South Africa: experiences from rural KwaZulu-Natal.

BACKGROUND: Adolescents in South Africa (SA) have a huge unmet need for sexual and reproductive health (SRH) services. Integrating such services into schools may overcome many of the current barriers to access. OBJECTIVES: We describe an SRH service model developed for high-school students and its implementation in 14 high schools in rural SA. METHODS: Following consultation with community and other key stakeholders about the demand for and acceptability of adolescent-targeted SRH services, a three-tier school-based model was developed that included: (i) in-school group SRH information and awareness sessions; (ii) in-school individual SRH counselling and customised HIV counselling and testing (CCT); and (iii) referrals to in-school fixed, in-school mobile or public sector primary SRH clinics. RESULTS: From October 2011 to June 2012, 70 consultative meetings were held. There was overwhelming support for the pilot founded on concerns about the high HIV prevalence and teenage pregnancy rates among adolescents in the community. SRH information was provided to 8 867 high-school students, 4 171 (47.0%) of whom accessed on-site CCT services for HIV. The gender-specific prevalence of HIV in these students was 3.3% (64/1 962) and 1.1% (24/2 209) for females and males, respectively. Two hundred and thirty-nine students (5.7%) were referred for clinical services at in-school fixed, in-school mobile or public sector primary SRH clinics. CONCLUSIONS: The SRH service provision pilot was acceptable in the community and seems feasible for scale-up. Further work is required to understand inter-school variability in uptake, identify additional service needs of students, and characterise SRH demand dynamics.

HIV infection in high school students in rural South Africa: role of transmissions among students.

In South Africa, adolescents constitute a key population at high risk of HIV acquisition. However, little is known about HIV transmission among students within schools. This study was undertaken to assess the risk factors for HIV infection and the extent of transmission among rural high school students. Between February and May 2012, consenting students from five randomly selected public sector high schools in rural KwaZulu-Natal participated in an anonymous cross-sectional survey. Dried blood spot samples were collected and tested for HIV. ß-Human chorionic gonadotropin (ßHCG) levels were measured in females for pregnancy. Family circumstances as well as sociodemographic and behavioral factors were assessed as potential risk factors. A subset (106/148, 72%) of HIV-positive samples underwent gag p17p24 sequencing for phylogenetic analysis. A total of 3,242 students (81.7% of enrolled students) participated. HIV prevalence was 6.8% [95% confidence interval (CI) 3.9-9.8%] in girls and 2.7% (CI 1.6-3.8%) in boys [adjusted odds ratio (aOR)=3.0, CI 2.4-3.8; p<0.001]. HIV prevalence increased from 4.6% (95% CI 1.9-7.3) in the 12- to 15-year-old girls to 23.1% (95% CI 7.7-38.5) in girls over 20 years, while in boys HIV prevalence increased from 2.7% (95% CI 0.6-4.9) in the 12- to15-year-old boys to 11.1% (95% CI 2.7-19.4) in those over 20 years. Sequencing of samples obtained from students revealed only two clusters, suggesting within-school transmission and three interschool clusters, while the remainder was most likely acquired from sources other than those currently found in students attending the school concerned. HIV prevalence in both girls (aOR=3.6, CI 2.9-4.5; p<0.001) and boys (aOR=2.8, CI 1.2-6.2; p=0.01) was higher in those without a living biological mother. The high burden of HIV infection among students was not associated with intraschool transmission in this rural setting. Lack of a living parent is an important factor defining high risk in this group of adolescents.

Prevalence of HIV, HSV-2 and pregnancy among high school students in rural KwaZulu-Natal, South Africa: a bio-behavioural cross-sectional survey.

OBJECTIVE: Adolescents in southern African high schools are a key population for HIV prevention interventions. We report on the prevalence of HIV, HSV-2 and pregnancy as indicators of high-risk sexual behaviour among high school students in rural KwaZulu-Natal. DESIGN: Bio-behavioural cross-sectional survey. METHODS: Students completed a self-administered structured, standardised demographic and sexual behavioural questionnaire. Dried blood spot specimens were collected for HIV and HSV-2 testing. Urine specimens were used for pregnancy testing in female students. RESULTS: A total of 2675 (1423 females, 1252 males) consenting students were enrolled from 14 high schools between September and November 2010. The median age of students was 16 years (IQR 15-18). HIV prevalence was 1.4% (95% CI 0.9 to 1.9) in males and 6.4% (95% CI 4.6 to 8.3) in females (p<0.001). HSV-2 prevalence was 2.6% (95% CI 1.6 to 3.7) in males and 10.7% (95% CI 8.8 to 12.6) in females (p<0.001). Pregnancy prevalence was 3.6% (95% CI 2.6 to 4.5). Risk factors for prevalent HIV infection in female students included being over 18 years of age (adjusted OR (aOR)=2.67, 95% CI 1.67 to 4.27; p<0.001), prevalent HSV-2 infection (aOR=4.35, 95% CI 2.61 to 7.24; p<0.001), previous pregnancy (aOR=1.66, 95% CI 1.10 to 2.51; p=0.016) and experience of two or more deaths in the household in the previous year (aOR=1.97, 95% CI 1.13 to 3.44; p=0.016). CONCLUSIONS: The high prevalence of HIV, HSV-2 and pregnancy underscore the need for school-based sexual and reproductive health services, and provide further impetus for the inclusion of adolescents in behavioural and biomedical trials with HIV incidence endpoints.

Disclosure of microbicide gel use to sexual partners: influence on adherence in the CAPRISA 004 trial.

Young women in sub-Saharan Africa are disproportionately affected by HIV, making the development of women initiated and controlled methods of prevention, including microbicides, a priority. Adherence is pivotal to microbicide efficacy and partner related factors are known to impact adherence. An analysis of disclosure of gel use to sexual partners and adherence in CAPRISA 004 women was conducted to better understand this relationship. Partner disclosure was significantly associated with a modest 4.2 % increased adherence (71.0 vs. 66.8 %, p = 0.03). Most women rated the experience of disclosure as positive, despite 6.7 % of partners expressing a negative reaction.Participants who disclosed were more likely to reside with their regular partner (14.4 vs. 8.4 %; p = 0.01) and reported consistent condom use at baseline (32.9 vs. 20.9 %; p < 0.01). Partner disclosure needs to be better understood as a potential facilitator or barrier to microbicide adherence.

HIV prevalence among high school learners - opportunities for school-based HIV testing programmes and sexual reproductive health services.

BACKGROUND: Young girls in sub Saharan Africa are reported to have higher rates of human immunodeficiency virus (HIV) infection compared to boys in the same age group. Knowledge of HIV status amongst high schools learners provides an important gateway to prevention and treatment services. This study aimed at determining the HIV prevalence and explored the feasibility of HIV testing among high school learners. METHODS: Between September 2010 and February 2011, a linked, anonymous cross-sectional survey was conducted in two public sector high schools in the rural KwaZulu-Natal midlands. Following written informed consent, dried blood spot samples (DBS) were collected and tested for HIV. The overall and age-specific HIV prevalence were compared with select demographic variables. RESULTS: The HIV prevalence in learners aged 12 to 25 in school A was 4.7% (95% CI 2.8-6.5) compared to 2.5% (95% CI 1.6-3.5) in school B, (p=0.04). Whilst the HIV prevalence was similar for boys at 1.3% (95% CI 0-2.8) in school A and 1.7% (95% CI 0.5-2.8) in school B, the prevalence in girls was consistently higher and was 7.7% (95% CI 4.5-10.9) in school A and 3.2% (95% CI 1.8-4.6) in school B. The age-specific HIV prevalence in girls increased 1.5 to 2 fold for each two year age category, while for boys the prevalence was stable across all age groups. CONCLUSIONS: The high HIV prevalence in female learners underscores the importance of sexual reproductive health and schools-based HIV testing programs as an important gateway to prevention and treatment services.

HIV incidence in young girls in KwaZulu-Natal, South Africa--public health imperative for their inclusion in HIV biomedical intervention trials.

Young women are particularly vulnerable for acquiring HIV yet they are often excluded from clinical trials testing new biomedical intervention. We assessed the HIV incidence and feasibility of enrolling a cohort of young women for potential participation in future clinical trials. Between March 2004 and May 2007, 594 HIV uninfected 14-30 year old women were enrolled into a longitudinal HIV risk reduction study in KwaZulu-Natal, South Africa. The overall HIV prevalence at screening in young girls below the age of 18 years was 27.6 % compared to 52.0 % in the women above 18 years, p < 0.001. HIV incidence was 4.7 [95 % Confidence interval (CI) 1.5-10.9) and 6.9 (95 % CI 4.8-9.6)/100 women years (wy), p = 0.42 and pregnancy rates were 23.7 (95 % CI 14.9-35.9) and 16.4 (95 % CI 12.9-20.6)/100 wy, p = 0.29, in the women below and above 18 years respectively. Retention was similar in both groups (71.0 vs. 71.5 %, p = 0.90). This study demonstrates that the inclusion of young girls between the ages of 14 and 17 years in longitudinal studies is feasible and their inclusion in clinical trials would maintain scientific integrity and power of the study.

HIV prevalence among high school learners - opportunities for schools-based HIV testing programmes and sexual reproductive health services.

BACKGROUND: Young girls in sub Saharan Africa are reported to have higher rates of human immunodeficiency virus (HIV) infection compared to boys in the same age group. Knowledge of HIV status amongst high schools learners provides an important gateway to prevention and treatment services. This study aimed at determining the HIV prevalence and explored the feasibility of HIV testing among high school learners. METHODS: Between September 2010 and February 2011, a linked, anonymous cross-sectional survey was conducted in two public sector high schools in the rural KwaZulu-Natal midlands. Following written informed consent, dried blood spot samples (DBS) were collected and tested for HIV. The overall and age-specific HIV prevalence were compared with select demographic variables. RESULTS: The HIV prevalence in learners aged 12 to 25 in school A was 4.7% (95% CI 2.8-6.5) compared to 2.5% (95% CI 1.6-3.5) in school B, (p = 0.04). Whilst the HIV prevalence was similar for boys at 1.3% (95% CI 0-2.8) in school A and 1.7% (95% CI 0.5-2.8) in school B, the prevalence in girls was consistently higher and was 7.7% (95% CI 4.5-10.9) in school A and 3.2% (95% CI 1.8-4.6) in school B. The age-specific HIV prevalence in girls increased 1.5 to 2 fold for each two year age category, while for boys the prevalence was stable across all age groups. CONCLUSIONS: The high HIV prevalence in female learners underscores the importance of sexual reproductive health and schools-based HIV testing programs as an important gateway to prevention and treatment services.

Counsellor-delivered HIV risk reduction intervention addresses safer sex barriers of people living with HIV in KwaZulu-Natal, South Africa.

This study developed an HIV risk reduction intervention for people living with HIV (PLWH) obtaining care at primary healthcare clinics in KwaZulu-Natal, South Africa by (1) conducting elicitation research to understand the dynamics of risk behaviour among PLWH, (2) modifying an existing HIV risk reduction intervention based on research findings and (3) conducting a pilot study to evaluate feasibility, acceptability and fidelity of the modified intervention implemented by trained lay counsellors at a rural clinic in KwaZulu-Natal. A total of 61 healthcare providers and 77 HIV+ patients from four primary healthcare clinics participated in 14 focus groups and 20 individual interviews to identify informational, motivational and behavioural skills (IMB) factors contributing to PLWH's sexual risk behaviour. Elicitation research findings were incorporated into a revised version of Options for Health, an evidence-based risk reduction intervention for PLWH in clinical care. In a 5-day training, lay counsellors learned strategies to address IMB barriers to safer sex identified in elicitation research. The revised intervention, which was implemented by six counsellors with 39 patients, was feasible to implement, acceptable to patients and counsellors, and implemented with good fidelity. This study makes an important contribution towards development of a theory-based HIV risk reduction intervention for PLWH linking prevention with treatment in South Africa.

Recruitment of high risk women for HIV prevention trials: baseline HIV prevalence and sexual behavior in the CAPRISA 004 tenofovir gel trial.

BACKGROUND: Young women in sub-Saharan Africa bear a disproportionate burden of HIV infection compared to men but have limited options to reduce their HIV risk. Microbicides could fill an important HIV prevention gap for sexually active women who are unable to successfully negotiate mutual monogamy or condom use. PURPOSE: This paper describes the baseline sample characteristics in the CAPRISA 004 trial which assessed the safety and effectiveness of the vaginal microbicide, 1% tenofovir gel for HIV prevention in South Africa. METHODS: This analysis assessed the baseline demographic, clinical and sexual behavior data of women screened and enrolled into the trial. The characteristics were summarized using descriptive summary measures; expressed as means and percent for categorical variables. RESULTS: HIV prevalence at screening was 25.8% [95% Confidence Interval (CI):23.9-27.7). Of the 889 eligibly enrolled women who contributed follow-up data, rural participants recruited from a family planning (FP) clinic were younger, more likely to be living apart from their regular partner, reported lower coital frequency, had lower condom use (p < 0.001). In contrast, urban participants recruited from a sexually transmitted disease (STD) clinic reported higher numbers of lifetime sexual partners, new partners in the last 30 days and receiving money in exchange for sex (p < 0.001). CONCLUSION: The populations selected provide suitable diverse target groups for HIV prevention intervention studies. TRIAL REGISTRATION: ClinicalTrials.gov: NCT 00441298.

Stabilizing HIV prevalence masks high HIV incidence rates amongst rural and urban women in KwaZulu-Natal, South Africa.

BACKGROUND: In mature generalized human immunodeficiency virus (HIV) epidemics, as survival from accessing antiretroviral treatment (ART) increases, HIV prevalence data may be suboptimal and difficult to interpret without HIV incidence rates. OBJECTIVE: To determine the HIV incidence rate among rural and urban women in KwaZulu-Natal, South Africa. METHODS: We conducted a prospective cohort study from March 2004 to May 2007. Volunteers were recruited from a rural family-planning clinic and an urban clinic for sexually transmitted infections. Consenting, HIV-uninfected women aged 14-30 years were enrolled. Demographic, clinical, sexual and behavioural data were collected using standardized questionnaires with HIV risk reduction counselling and HIV testing. Pelvic examinations were completed at quarterly visits. RESULTS: The HIV prevalence at screening was 35.7% [95% confidence interval (CI) 32.7-38.8] amongst rural women and 59.3% (95% CI 56.5-62.0) amongst urban women. A total of 594/2240 (26.5%) enrolled women contributed to 602 person-years (PYs) of follow-up. The median age was 22 years [inter-quartile range 18-23 years]. HIV incidence rate was 6.5/100 PY (95% CI 4.4-9.2) amongst rural women and 6.4/100 PY (95% CI 2.6-13.2) amongst urban women. HIV incidence rate of 17.2/100 PY (95% CI 2.1-62.2) was highest amongst urban women <20 years of age and 10.2/100 PY (95% CI 4.1-20.9) amongst rural women ≥ 25 years of age. CONCLUSION: HIV incidence rates are devastatingly high in young women in rural and urban KwaZulu-Natal, despite reports of stabilized HIV prevalence observed in current surveillance data. The diffuse nature of the HIV epidemic underscores the urgent need to enhance HIV prevention and treatment modalities.

Effectiveness and safety of tenofovir gel, an antiretroviral microbicide, for the prevention of HIV infection in women.

The Centre for the AIDS Program of Research in South Africa (CAPRISA) 004 trial assessed the effectiveness and safety of a 1% vaginal gel formulation of tenofovir, a nucleotide reverse transcriptase inhibitor, for the prevention of HIV acquisition in women. A double-blind, randomized controlled trial was conducted comparing tenofovir gel (n = 445 women) with placebo gel (n = 444 women) in sexually active, HIV-uninfected 18- to 40-year-old women in urban and rural KwaZulu-Natal, South Africa. HIV serostatus, safety, sexual behavior, and gel and condom use were assessed at monthly follow-up visits for 30 months. HIV incidence in the tenofovir gel arm was 5.6 per 100 women-years (person time of study observation) (38 out of 680.6 women-years) compared with 9.1 per 100 women-years (60 out of 660.7 women-years) in the placebo gel arm (incidence rate ratio = 0.61; P = 0.017). In high adherers (gel adherence > 80%), HIV incidence was 54% lower (P = 0.025) in the tenofovir gel arm. In intermediate adherers (gel adherence 50 to 80%) and low adherers (gel adherence < 50%), the HIV incidence reduction was 38 and 28%, respectively. Tenofovir gel reduced HIV acquisition by an estimated 39% overall, and by 54% in women with high gel adherence. No increase in the overall adverse event rates was observed. There were no changes in viral load and no tenofovir resistance in HIV seroconverters. Tenofovir gel could potentially fill an important HIV prevention gap, especially for women unable to successfully negotiate mutual monogamy or condom use.

Evolution of epidemiologic methods and concepts in selected textbooks of the 20th century.

Textbooks are an expression of the state of development of a discipline at a given moment in time. By reviewing eight epidemiology textbooks published over the course of a century, we have attempted to trace the evolution of five epidemiologic concepts and methods: study design (cohort studies and case-control studies), confounding, bias, interaction and causal inference. Overall, these eight textbooks can be grouped into three generations. Greenwood (1935) and Hill (first edition 1937; version reviewed 1961)'s textbooks belong to the first generation, "early epidemiology", which comprise early definitions of bias and confounding. The second generation, "classic epidemiology", represented by the textbooks of Morris (first edition 1957; version reviewed 1964), MacMahon & Pugh (first edition 1960; version reviewed 1970), Susser (1973), and Lilienfeld & Lilienfeld (first edition 1976; version reviewed 1980), clarifies the properties of cohort and case-control study designs and the theory of disease causation. Miettinen (1985) and Rothman (1986)'s textbooks belong to a third generation, "modern epidemiology", presenting an integrated perspective on study designs and their measures of outcome, as well as distinguishing and formalizing the concepts of confounding and interaction. Our review demonstrates that epidemiology, as a scientific discipline, is in constant evolution and transformation. It is likely that new methodological tools, able to assess the complexity of the causes of human health, will be proposed in future generations of textbooks.